2025-07-12

Disorder-induced spin excitation continuum and spin-glass ground state in the inverse spinel CuGa2O4

Our group published a paper with the same title in Physical Review B, reporting the discovery of a disorder-induced spin excitation continuum and a spin-glass ground state in the inverse spinel compound CuGa₂O₄ [Phys. Rev. B 112, 035128 (2025)]. This work is a result of collaboration among researchers from our School of Physics, Hubei Normal University, and Brookhaven National Laboratory.

CuGa₂O₄ belongs to the AB₂O₄ spinel family, a group of compounds known for their highly frustrated structures and potential to host exotic magnetic states. In this study, we performed comprehensive measurements including neutron scattering, magnetic susceptibility, and specific heat to investigate its low-temperature magnetic properties. Remarkably, no long-range magnetic order was detected down to 80 mK, and inelastic neutron scattering revealed a broad gapless continuum of magnetic excitations around the Brillouin zone boundary, resembling the magnetic excitation spectra expected for a quantum spin liquid. Nevertheless, a spin-freezing transition at T_f ≈ 0.88 K is identified from the cusp in the dc susceptibility curves, where a bifurcation between zero-field-cooling and field-cooling curves occurs. Furthermore, ac susceptibility measurements show a peak close to T_f at low frequency, which shifts to higher temperature with increasing frequency. These signatures are hallmarks of a spin-glass state, where the magnetic moments become frozen in a disordered configuration with strong antisite disorder between Cu²⁺ and Ga³⁺ ions. These results show that CuGa₂O₄ has a spin-glass ground state, consistent with the establishment of short-range order inferred from the specific-heat measurements.

This study emphasizes that disorder can mimic features of quantum spin liquids and plays a crucial role in shaping spin dynamics in frustrated systems. Our findings not only advance the understanding of disorder effects in spinel compounds but also provide a new perspective on how to design and explore quantum magnets.

2025-05-18

Celebrating Our Achievers: Dr. Junbo Liao, Rising Physicist, and Dr. Zhentao Huang, Frontier Neutron Scientist

We are proud to celebrate the successful Ph.D. thesis defenses of two outstanding members of our research group, Dr. Junbo Liao and Dr. Zhentao Huang, on May 16th.

Dr. Junbo Liao has distinguished himself through unwavering dedication to research in condensed matter physics. Throughout his doctoral studies, he not only carried out rigorous and insightful experiments but also showed strong initiative in self-studying a broad range of theoretical frameworks to deepen his understanding. This rare combination of hands-on skill and theoretical depth has greatly enriched his scientific perspective. We are delighted that Dr. Liao will continue his academic journey as a postdoctoral researcher in our group, where his passion and curiosity are sure to lead to further discoveries. 

Dr. Zhentao Huang has likewise completed an impressive doctoral journey. With a meticulous approach and a keen eye for subtle signals, he excels at uncovering hidden physical phenomena. His postdoctoral work already reflects strong analytical depth and originality. Dr. Huang will soon join the China Spallation Neutron Source (CSNS), where he will devote himself to developing the country’s first time-of-flight inelastic neutron scattering spectrometer—a landmark project that promises to open new frontiers in neutron science in China. 

Please join us in congratulating Dr. Liao and Dr. Huang on these remarkable accomplishments. We look forward to their continued contributions to the advancement of science.

2025-04-24

Magnetically disordered ground state in the triangular-lattice antiferromagnets Rb3Yb(VO4)2 and Cs3Yb(VO4)2

Our group published a paper entitled “Magnetically disordered ground state in the triangular-lattice antiferromagnets Rb₃Yb(VO₄)₂ and Cs₃Yb(VO₄)₂” in Physical Review B [Phys. Rev. B 111, 155141 (2025)] in collaboration with the group led by our group alumni Prof. Zhen Ma at Hubei Normal University. 

Quantum spin liquids (QSLs) represent a unique quantum state of matter that hosts long-range quantum entanglement and fractional excitations. However, structural disorder resulting from site mixing between different types of ions usually arises in real QSL candidates, which is considered to be an obstacle to gaining insights into the intrinsic physics. In this work, we have synthesized two new rare-earth compounds Rb₃Yb(VO₄)₂ and Cs₃Yb(VO₄)₂. X-ray diffractions reveal a perfect triangular-lattice structure with no detectable disorder. Magnetic susceptibility measurements do not capture any phase transition or spin freezing down to 1.8 K. Specific-heat results show no sign of long-range magnetic order down to ∼0.1 K, but only a Schottky anomaly that is continuously mediated by the external magnetic fields. Additionally, inelastic neutron scattering is employed to detect low-energy spin excitations in Rb₃Yb(VO₄)₂. The absence of magnetic excitation signals as well as static magnetic order down to 97 mK aligns with the results from magnetic susceptibility and specific heat. Collectively, these findings point to a quantum disordered ground state and provide a promising platform for further exploration of quantum magnetism in this pristine disorder-free system.

2025-02-05

Significant chiral magnetotransport magnified by multiple Weyl nodes.

Our group, in collaboration with Professor Rui Wang, has published a paper entitled "Significant chiral magnetotransport magnified by multiple Weyl nodes" in Physical Review B [Phys. Rev. B 111, 045163 (2025)]. 

The intertwining of magnetism with topology is known to give rise to exotic quantum phenomena. In this work, we explore the magnetotransport properties of NdAlSi, a magnetic Weyl semimetal that spontaneously breaks inversion and time-reversal symmetries and hosts a large number of Weyl nodes. We observe a significant negative magnetoresistance, which we attribute to the chiral anomaly associated with multiple Weyl nodes. Remarkably, the extracted chiral coefficient reaches approximately 52 mΩ⁻¹ m⁻¹ T⁻², larger than many other topological materials. Additionally, we observe an exotic anomalous Hall effect with an out-of-sync behavior, where the anomalous Hall resistance does not exactly follow the field dependence of the magnetization, in contrast to that in conventional ferromagnets. These rich quantum transport phenomena, driven by the interplay between magnetism and Weyl nodes, establish NdAlSi as a prime platform for exploring the intricate topological behaviors of magnetic Weyl semimetals.

2025-01-15

Magnetic interactions in the polar ferrimagnet Mn2Mo3O8 with a bipartite structure.

Our group published a paper entitled "Magnetic interactions in the polar ferrimagnet Mn₂Mo₃O₈ with a bipartite structure" in Physical Review B [Phys. Rev. B 111, 024407 (2025)]. 

The polar magnets A₂Mo₃O₈ (A = Fe, Mn, Co, and Ni) feature a bipartite structure, where the magnetic A²⁺ ions occupy two different sites with octahedral and tetrahedral oxygen coordination. This bipartite structure provides a platform for the emergence of nontrivial magnetoelectric effects and intriguing excitation behaviors, and thus stimulates significant research interest. In this work, we conduct inelastic neutron scattering measurements on single crystals of Mn₂Mo₃O₈, an L-type ferrimagnet of the A₂Mo₃O₈ family, to investigate its spin dynamics. The obtained magnetic excitation spectra reveal two distinct magnon branches corresponding to the octahedral and tetrahedral spins in Mn₂Mo₃O₈. These magnon bands can be well described by a spin Hamiltonian including Heisenberg and single-ion anisotropy terms. Employing our effective spin model, we successfully reproduce the unusual temperature dependence of the L-type ferrimagnetic susceptibility through self-consistent mean-field theory. Our research reveals the significance of the bipartite structure in determining the excitation properties of the polar magnets A₂Mo₃O₈ and provides valuable insights into the spin dynamics of L-type ferrimagnets.

2024-12-31

Happy New Year!

Happy New Year 2025! 

May this year bring you endless joy, success, and good health!

Let’s embrace the future with hope, courage, and boundless possibilities!

2024-11-16

Group members awarded for "Excellent Doctoral Thesis"!

Yanyan Shangguan, graduated from our group in 2023, was awarded "Excellent Doctoral Thesis" by the University, with Thesis entitled "Neutron Scattering Investigations on Quantum Magnets Na₃Ni₂BiO₆ and Na₂Cu₂TeO₆". As her advisor, Prof. Wen was awarded "Advisor of Excellent Doctoral Thesis" accordingly. Congratulations to them and the group!

2024-10-28

Absence of Altermagnetic Spin Splitting Character in Rutile Oxide RuO2

Our research group, in collaboration with Professor Dawei Shen from the University of Science and Technology of China, has published a PRL paper on RuO₂, a candidate material of altermagnetism [Phys. Rev. Lett. 133, 176401 (2024)]. 

Altermagnetism, a novel magnetic ordering state described based on spin space groups rather than magnetic space groups, has recently been theoretically predicted and has garnered significant attention. It is characterized by unconventional antiferromagnetic-like magnetic order with zero net magnetization, while exhibiting ferromagnetic-like-split energy bands. These features endow altermagnets with great potential for applications in spintronic devices. 

RuO₂ was previously considered to be one of the most promising candidate materials for altermagnetism. In this work, we investigate the electronic structure of RuO₂ to explore whether it is an altermagnet or not. We grew high-quality RuO₂ single crystals. Utilizing spin- and angle-resolved photoemission spectroscopy, our collaborators find that the band structure of RuO₂ indeed aligns with the non-magnetic ground state. Meanwhile, we identify anomalous in-plane polarization of the low-lying bulk bands that contradict the d-wave symmetry predicted for altermagnetism. These findings challenge the altermagnetic order previously proposed for RuO₂, prompting a reevaluation of its magnetic properties.

2024-06-08

Spin and lattice dynamics in the van der Waals antiferromagnet MnPSe3

Our group published a paper entitled "Spin and lattice dynamics in the van der Waals antiferromagnet MnPSe₃" in Physical Review B [Phys. Rev. B 109, 224411 (2024)]. MnPSe₃ is a member of the antiferromagnetic van der Waals family MPX₃ (where M can be Fe, Mn, Co, or Ni, and X can be S or Se). In our study, we performed inelastic neutron scattering measurements on single-crystal samples of MnPSe₃ to investigate the spin dynamics and determine the effective spin model. The magnon bands observed are well-described by a spin model that includes a Heisenberg term with three intraplane exchange parameters (J₁=−0.73 meV, J₂=−0.014 meV, J₃=−0.43 meV) and one interplane exchange parameter (J_c=−0.054 meV), along with an easy-plane single-ion anisotropy term (D=−0.035 meV). Additionally, we observed the intersection of magnon and phonon bands. However, in the intersecting region, no anomalous spectral features indicating the formation of magnon-phonon hybrid excitations were detected. This work provides comprehensive characterizations on the spin and lattice dynamics in this material.

2024-04-24

Possible gapless quantum spin liquid behavior in the triangular-lattice Ising antiferromagnet PrMgAl11O19

Our group published a paper entitled “Possible gapless quantum spin liquid behavior in the triangular-lattice Ising antiferromagnet PrMgAl₁₁O₁₉” in PRB [Phys. Rev. B 109, 165143 (2024)] in collaboration with the group led by our group alumni Prof. Zhen Ma at Hubei Normal University. Quantum spin liquids (QSLs) represent a novel state where spins are highly entangled but do not order even at zero temperature due to strong quantum fluctuations. Such a state is mostly studied in Heisenberg models defined on geometrically frustrated lattices. In this work, we turn to a new triangular-lattice antiferromagnet PrMgAl₁₁O₁₉, in which the interactions are believed to be of Ising type. Magnetic susceptibility measured with an external field along the c axis is two orders of magnitude larger than that with a field in the a-b plane, showcasing an ideal easy-axis behavior. Meanwhile, there is neither magnetic phase transition nor spin freezing observed down to 1.8 K. Ultralow-temperature specific heat measured down to 50 mK does not capture any phase transition either, but a hump at 4.5 K, below which the magnetic specific heat exhibits a quasiquadratic temperature dependence that is consistent with a Dirac QSL state. Inelastic neutron scattering experiments reveal a gapless broad continuum of low-energy magnetic excitation at the base temperature 55 mK, in favor of the realization of a gapless QSL. These results provide a scarce example for the QSL behaviors observed in an Ising-type magnet, which can serve as a promising platform for future research on QSL physics based on an Ising model.

2024-01-30

Microscopic origin of the spin-reorientation transition in the kagome topological magnet TbMn6Sn6

Our group published a paper with the same title in Physical Review B, reporting the observation of magnetic excitations in a kagome topological magnet TbMn₆Sn₆ [Phys. Rev. B 109, 014434 (2024)]. The collaborative effort involved researchers from our School of Physics, as well as those from Nanjing University of Posts and Telecommunications, and Zhejiang University.

TbMn₆Sn₆, a correlated topological magnet featuring a Mn-based kagome lattice, exhibits a fascinating Chern gap opening at the Dirac point at low temperatures. In this study, we employed neutron scattering techniques to delve into the spin-reorientation transition in TbMn₆Sn₆. We find the coexistence of two Tb modes at 200 K, which can be understood using a model based on the SU(N) spin-wave theory. This model takes into account the temperature-dependent evolution of the ground state Tb 4f orbitals, influenced by factors such as crystalline electric field, single-ion anisotropy, and exchange interactions between Tb and Mn ions. The interplay leads to a change of the Tb 4f ground state and drives the spin-reorientation transition in TbMn₆Sn₆. Notably, our work highlights the similarity between the coupling of localized Tb 4f moments and itinerant Mn d electrons with the widely-discussed Kondo effect in heavy fermion systems where the Kondo physics is purely dominated by f electrons.

Building on our recent exploration of the Kondo effect in d-electron systems [Phys. Rev. X 12, 011022(2022)], this study broadens the applicability of Kondo physics to various classes of condensed matter systems. The intricate interplay of factors in TbMn₆Sn₆ successfully explain the spin-reorientation transition and underscores the versatility of Kondo physics in diverse condensed matter phenomena.

2023-12-31

Happy New Year！

Happy New Year to all!

Cheers to a brand new year filled with endless possibilities and exciting adventures!

2023-09-30

Topological magnon polarons in Fe2Mo3O8

Our group published a paper entitled “Direct observation of topological magnon polarons in a multiferroic material” in Nature Communications [Nat. Commun. 14, 6093 (2023)] in collaboration with Prof. Jian-Xin Li’s group at our School of Physics. Magnons and phonons, quanta of spin waves and lattice vibrations respectively, constitute two fundamental collective excitations in ordered magnets. When these two entities are strongly coupled, intriguing collective excitations known as magnon polarons can emerge. They possess hybrid magnonic and phononic signatures, and are responsible for many exotic spintronic and magnonic phenomena. They can provide a phonon-involved way to generate and manipulate spin currents carried by magnons thanks to their hybrid nature, signifying promising potentials in spintronics technology. Despite long-term sustained experimental efforts in chasing for magnon polarons, direct spectroscopic evidence of their existence is hardly observed. In this work, we report the direct observation of magnon polarons using neutron spectroscopy on a multiferroic Fe₂Mo₃O₈. We unambiguously identify two distinct hallmarks of magnon polarons: the appearance of a gap at the nominal intersection of the original magnon and phonon bands, along with mixing, interconverting and reversing between the magnonic and phononic components. We attribute the formation of magnon polarons to the strong magnon-phonon coupling induced by Dzyaloshinskii-Moriya interaction. Intriguingly, we find that the band-inverted magnon polarons are topologically nontrivial. These results uncover exotic elementary excitations arising from the magnon-phonon coupling, and offer a new route to topological states by considering hybridizations between different types of fundamental excitations. Our work, in conjunction with our recent publication in Nature Physics [Nat. Phys. 19, 1868 (2023)], underscores the emergence of novel phenomena driven by the strong magnon-phonon coupling. More details can be found here.

2023-09-26

Our group’s second paper in Nature Physics

Our group published a paper entitled “A one-third magnetization plateau phase as evidence for the Kitaev interaction in a honeycomb-lattice antiferromagnet” in Nature Physics [Nat. Phys. 19, 1883 (2023)] in collaboration with Prof. Jian-Xin Li’s group at our School of Physics, and Prof. Wei Li’s group at Institute of Theoretical Physics, CAS. 

Frustration plays an essential role in quantum magnets. The frustration-induced quantum fluctuation could avoid the formation of ordered magnetic ground states, and lead to magnetically disordered phases such as the quantum spin liquids. On the other hand, the quantum fluctuation can lift the degeneracy of the ground state and select a specific spin state within a finite range of external magnetic field; this gives rise to an exotic magnetization plateau phase in which the magnetization is a fraction of its saturation value. Since frustration is a prerequisite for the fractional magnetization plateau phase, whether it will occur in a genuine honeycomb lattice in which geometrical frustration as that occurs in triangular and Kagome lattices is absent, and how to understand it if it does occur, remain outstanding questions. In this work, we report comprehensive thermodynamic and neutron scattering measurements on high-quality single crystals of the spin-1 honeycomb-lattice antiferromagnet Na₃Ni₂BiO₆. We show that the magnetization curve has a definite plateau at 1/3 of the saturation magnetization between 5.2 and 7.4 T at 2 K. By performing elastic neutron scattering measurements, we obtain complete contour maps for the magnetic Bragg peaks in the (H, K, 0) plane in zero field and in the plateau phase. By comparing experimental results with calculations, we propose the microscopic magnetic configuration of the 1/3 magnetization plateau phase to be a zero-up-zero-down-up-up (○↑○↓↑↑) ferrimagnetic state. Our density-functional-theory and tensor-network calculations show that a minimal model with Heisenberg exchange couplings J, a bond-dependent anisotropic Kitaev interaction K and a single-ion anisotropy term D can well explain the experimental observations. In particular, the Kitaev interaction, which was demonstrated to exist in α-RuCl₃ in our early work [Phys. Rev. Lett. 118, 107203 (2017)], leads to the exchange frustration and stabilizes the one-third-plateau phase. This work not only extends the study of the fractional magnetization plateau phase to honeycomb-lattice compounds which conventionally do not exhibit geometrical frustrations, but also expands the territory of quantum magnets that host Kitaev physics from S = 1/2 to higher-spin systems. More details can be found here.

2023-09-15

Paper on Fe2Mo3O8 published in Nature Physics

Our group published a paper entitled “Fluctuation-enhanced phonon magnetic moments in a polar antiferromagnet” in Nature Physics [Nat. Phys. 19, 1868 (2023)] in collaboration with Prof. Qi Zhang’s group at our School of Physics. 

Phonons are the quasiparticles of collective lattice excitations that may carry finite angular momenta, but commonly exhibit negligible magnetic moments. A large phonon magnetic moment enables the direct mutual control of magnetic orders and lattice motions, and could be applied to develop spin–phononic devices. Despite reports of large phonon magnetic moments in some non-magnetic and paramagnetic systems, such phenomena have not yet been discovered in magnetically ordered systems. Furthermore, the roles of many-body correlations and fluctuations in phonon magnetism remain unclear. In this work, combining magneto-Raman spectroscopy and inelastic neutron scattering measurements on a polar antiferromagnet Fe₂Mo₃O₈, we show that a pair of low-lying chiral phonons carry large magnetic moments (0.11μ_B). Additionally, we observe a sixfold enhancement in the phonon magnetic moment in the vicinity of the Néel temperature. A microscopic model based on the coupling between phonons and both magnons and paramagnons accounts for the experimental observations. These findings present a new paradigm in the study of phonon magnetism, where the many-body correlations, instead of single-particle interactions, play key roles. It further establishes Fe₂Mo₃O₈ as an ideal platform for exploring phonon magnetism and developing hybrid phononic and spintronic devices. More details can be found here.

2023-05-21

Celebrating Our Achievers: Dr. Yanyan Shangguan, Aspiring Physicist, and Xiaoxue Zhao, Future High School Educator

We are thrilled to announce the successful thesis defenses of two of our distinguished students, Dr. Yanyan Shangguan and Xiaoxue Zhao, on May 19th.

Dr. Yanyan Shangguan has reached a significant milestone in her academic journey by successfully defending her PhD thesis. Her unwavering dedication, rigorous efforts, and intellectual prowess throughout her doctoral studies have led her to this momentous achievement. Her groundbreaking research in physics has deepened our understanding of the subject and promises to contribute further in the field as she continues her research journey. 

Just as commendable is Xiaoxue Zhao's successful Master's thesis defense. Her dedication, resilience, and exceptional scholarship throughout her Master's studies is truly inspiring. Her future as a high school teacher will undoubtedly be enriched by this accomplishment, and we anticipate that she will inspire a new generation of learners with her passion for education. 

Join us in congratulating Dr. Yanyan Shangguan and Xiaoxue Zhao on these notable accomplishments! We eagerly anticipate their future contributions to the worlds of physics and education, respectively.

2023-04-27

Signatures of a gapless quantum spin liquid in a Kitaev material Na3Co2-xZnxSbO6

Our group published a paper entitled “Signatures of a gapless quantum spin liquid in a Kitaev material Na₃Co_2-xZn_xSbO₆” in PRB [Phys. Rev. B 107, 165143 (2023)] in collaboration with the group led by our group alumni Prof. Zhen Ma at Hubei Normal University. In our recent work, we have demonstrated the significant role of Zn doping in suppressing the magnetic order and inducing quantum paramagnetic behaviors in a 3d based Kitaev magnet Na₂Co₂TeO₆ [Phys. Rev. Mater. 7, 014407 (2023)]. In this work, we show results associated with a gapless quantum spin liquid (QSL) in another Kitaev cobaltate Na₃Co_2-xZn_xSbO₆. X-ray diffraction characterizations reveal no structural transition but quite tiny changes on the lattice parameters over our substitution range 0≤x≤0.4. Magnetic susceptibility and specific heat results both show that antiferromagnetic (AFM) transition temperature is continuously suppressed with increasing Zn content x and neither long-range magnetic order nor spin freezing is observed when x≥0.2. More importantly, a linear term of the specific heat representing fermionic excitations is captured below 5 K in the magnetically disordered regime, as opposed to the C_m∝T³ behavior expected for bosonic excitations in the AFM state. These results indicate the presence of gapless fractional excitations in the samples with no magnetic order, evidencing a potential QSL state induced by doping in a Kitaev system.

2023-03-10

Prof. Wen received the “Outstanding Reviewer Awards” from IOP Publishing

Prof. Wen was recognized as an Outstanding Reviewer for Chinese Physics Letters for the year 2022 and granted the “Outstanding Reviewer Awards” from IOP Publishing. Congratulations!

2023-01-20

Suppression of the antiferromagnetic order by Zn doping in a possible Kitaev material Na2Co2TeO6

Our group published a paper entitled “Suppression of the antiferromagnetic order by Zn doping in a possible Kitaev material Na₂Co₂TeO₆” in PRM [Phys. Rev. Mater. 7, 014407 (2023)] in collaboration with the group led by our group alumni Prof. Zhen Ma at Hubei Normal University. A 3d based honeycomb cobaltate Na₂Co₂TeO₆ has attracted enormous attention due to the proposed proximity to the Kitaev spin-liquid state as its 4d/5d counterparts. In this work, we partially substitute magnetic Co²⁺ with nonmagnetic Zn²⁺ in Na₂Co₂TeO₆ in an extensive range and perform structural, magnetic, and thermodynamic studies to investigate the doping evolution of the magnetic ground states. X-ray diffractions reveal no structural transition but only minor changes on the lattice parameter c over a wide substitution range 0≤x≤1.5. Magnetic susceptibility and specific heat measurements both show a suppression of long-range magnetic order with increasing zinc content. After x∼1.0, it develops into a spin-glass state with short-range order, which is rapidly supplanted by a magnetically disordered state when x≥1.3. These results explicitly track the evolution process of the magnetic ground states and establish a magnetic phase diagram of Na₂Co_2−xZn_xTeO₆. Zn doping may serve as a feasible way to enhance quantum fluctuations and induce quantum paramagnetic behaviors that may provide insights about the Kitaev physics.

2022-12-31

Happy New Year!

Happy New Year to all! Wish all have a wonderful 2023! 

2022-11-21

Works on α-RuCl3 won "Best Poster Prize" at the CPS Fall Meeting!

Earlier this year, our group published two papers reporting evidence of the fractional excitations for the Kitaev quantum-spin-liquid candidate α-RuCl₃ in Chinese Physics Letters as Express Letters [CPL 39, 057501 (2022); CPL 39, 027501 (2022)]. Based on these results, Kejing Ran, former PhD student of the group and now working at ShanghaiTech, gave a poster presentation at the 2022 Chinese Physical Society's Fall Meeting held in Shenzhen. The poster entitled “Evidence for Magnetic Fractional Excitations in a Kitaev Quantum-Spin-Liquid Candidate” was awarded the "Best Poster Prize". Congratulations to Kejing and the group!

2022-09-27

Group members awarded for "Excellent Doctoral Thesis"!

Song Bao, graduated from our group in 2021, was awarded "Excellent Doctoral Thesis" by the University, with Thesis entitled "Spin and Lattice Dynamics of the Magnetic Topological Materials Cu₃TeO₆ and Fe_3-xGeTe₂".  As his advisors, Prof. Wen and our long-term collaborator, Prof. Li, were awarded "Advisor of Excellent Doctoral Thesis" accordingly. Congratulations to them and the group!

2022-08-23

Congratulations to Prof. Wen for being granted the Distinguished Young Scholars Fund (国家杰青) by NSFC

On August, 9th, Prof. Wen was officially notified by National Science Foundation of China (NSFC) that he was granted "The National Science Fund for Distinguished Young Scholars"（国家杰出青年科学基金）. Congratulations to him for this great achievement! This is also the accomplishment of the whole Neutron Scattering Group, and a wonderful outcome of the sustained efforts of all the former and present group members. With this generous funding support (4 million RMB) from NSFC, the group will work harder and more creatively on “Neutron Spectroscopy Study on Quantum Magnetism”, and make more breakthroughs by discovering novel quantum magnets and finding exotic elementary excitations, using the state-of-the-art neutron spectroscopy as well as thermal conductivity measurements.

2022-06-22

Enhanced low-energy magnetic excitations evidencing the Cu-induced localization in the Fe-based superconductor Fe0.98Te0.5Se0.5

Our group published a paper entitled “Enhanced low-energy magnetic excitations evidencing the Cu-induced localization in the Fe-based superconductor Fe_0.98Te_0.5Se_0.5” in PRB [Phys. Rev. B 105, 245129 (2022)]. Understanding the doping effect is key to the understanding of the interplay between superconductivity and magnetism in iron-based superconductors. In this work, we have performed inelastic neutron scattering measurements on optimally doped Fe_0.98Te_0.5Se_0.5 and 10% Cu-doped Fe_0.88Cu_0.1Te_0.5Se_0.5 to investigate the doping effects on the spin excitations in the whole energy range up to 300 meV. It is found that substitution of Cu for Fe enhances the low-energy spin excitations (≤100 meV), especially around the (0.5, 0.5) point, and leaves the high-energy magnetic excitations intact. In contrast to the expectation that Cu with spin 1/2 will dilute the magnetic moments contributed by Fe with a larger spin, we find that the 10% Cu doping enlarges the effective fluctuating moment from 2.85 to 3.13 μ_B/Fe, although there is no long- or short-range magnetic order around (0.5, 0.5) and (0.5, 0). The presence of enhanced magnetic excitations in the 10% Cu doped sample which is in the insulating state indicates that the magnetic excitations must have some contributions from the local moments, reflecting the dual nature of the magnetism in iron-based superconductors. We attribute the substitution effects to the localization of the itinerant electrons induced by Cu dopants. These results also indicate that the Cu doping does not act as electron donor as in a rigid-band shift model, but more as scattering centers that localize the system, enhance the local moments and suppress the superconductivity.

2022-04-10

Neutron Spectroscopy Evidence for a Possible Magnetic-Field-Induced Gapless Quantum-Spin-Liquid Phase in a Kitaev Material α-RuCl3

Our group published a paper entitled “Neutron Spectroscopy Evidence for a Possible Magnetic-Field-Induced Gapless Quantum-Spin-Liquid Phase in a Kitaev Material α-RuCl₃” in CPL as Express Letter [Chin. Phys. Lett. 39, 057501 (2022)]. So far, α-RuCl₃ has been the most promising Kitaev quantum-spin-liquid (QSL) candidate, but its ground state exhibits a long-range zigzag magnetic order, which defies the QSL phase. Nevertheless, the magnetic order is fragile and can be completely suppressed by applying an external magnetic field. In this work, we explore the evolution of the magnetic excitations of α-RuCl₃ under an in-plane magnetic field, by carrying out inelastic neutron scattering measurements on high-quality single crystals. We find that on the verge of the critical field 7.5 T, the continuum representing the fractional excitations near the Γ point still exists, while the spin-wave excitations near the M point associated with the zigzag magnetic order vanish, which indicates the emergence of a pure QSL state. By following the gap evolution with field, we establish a three-zone phase diagram, containing a low-field gapped zigzag order phase, an intermediate-field gapless QSL, and a high-field gapped partially polarized state. These results demonstrate that an in-plane magnetic field can drive α-RuCl₃ into a long-sought QSL state near the critical field.

2022-02-03

Neutron Spectroscopy Evidence on the Dual Nature of Magnetic Excitations in a van der Waals Metallic Ferromagnet Fe2.72GeTe2

Our group published a paper entitled “Neutron Spectroscopy Evidence on the Dual Nature of Magnetic Excitations in a van der Waals Metallic Ferromagnet Fe_2.72GeTe₂” in PRX [Phys. Rev. X 12, 011022 (2022)]. Magnetism has been a long and mysterious issue in condensed matter physics. Its understanding can usually be divided into two opposite camps: the local-moment or itinerant picture. But in the intermediate range where both local moments and itinerant electrons are present, the nature of magnetism remains elusive. Here, by performing inelastic neutron scattering on a van der Waals metallic ferromagnet Fe_2.72GeTe₂, which can sustain tunable room-temperature ferromagnetism down to the monolayer limit, we found the spin excitations are composed of a dispersive mode at low energies and a columnlike continuum at high energies, resulting from local moments and itinerant electrons, respectively. Moreover, we also found that the low-energy spin waves at 100 K are more coherent than those at 4 K, which is evidence of the weakening of the Kondo screening at high temperatures. These results unambiguously demonstrate the coexistence of local moments and itinerant electrons and the Kondo effect between these two components in Fe_2.72GeTe₂. These findings shed light on the understanding of magnetism in transition-metal compounds. More details can be found here.

2021-12-31

Happy New Year!

Happy New Year to all! Wish all have a wonderful 2022! 

2021-12-31

Disorder-induced broadening of the spin waves in the triangular-lattice quantum spin liquid candidate YbZnGaO4

Our group published a paper entitled “Disorder-induced broadening of the spin waves in the triangular-lattice quantum spin liquid candidate YbZnGaO₄” in PRB [Phys. Rev. B 104, 224433 (2021)]. Disorder is important in the study of quantum spin liquids (QSLs), but as we demonstrated previously, its role on the spin dynamics remains elusive [Phys. Rev. Lett. 120, 087201 (2018); Phys. Rev. B 102, 224415 (2020); Nat. Commun. 11, 5631 (2020)]. In this work, we explore the disorder effect by performing inelastic neutron scattering (INS) on the triangular-lattice QSL candidate YbZnGaO4 under a c-axis magnetic field. With an intermediate field of 2.5 T, the broad continuum of magnetic excitations measured at zero field becomes more smeared both in energy and momentum. When a field up to 10 T drives the system into a fully polarized state, we observe clear spin-wave excitations with a gap of 1.4 meV comparable to the bandwidth. However, different from the sharp and well-defined spin waves expected for a clean ferromagnetic state, the spectra exhibit strong broadening in energy and momentum. By considering the disorder effect arising from the random site mixing of nonmagnetic Zn²⁺ and Ga³⁺ ions, our classical Monte Carlo simulations can well reproduce the INS spectra both at zero and high fields. These results elucidate the critical role of disorder in broadening the magnetic excitation spectra and mimicking the spin-liquid features in frustrated quantum magnets.

2021-12-31

Evidence for Magnetic Fractional Excitations in a Kitaev Quantum-Spin-Liquid Candidate α-RuCl3

Our group published a paper entitled "Evidence for Magnetic Fractional Excitations in a Kitaev Quantum-Spin-Liquid Candidate α-RuCl₃" in CPL as Express Letter [Chin. Phys. Lett. 39, 027501 (2022)]. α-RuCl₃ is by far the most promising candidate for Kitaev quantum-spin-liquid (QSL) material. In 2017 and 2018, our group has determined the dominant Kitaev interaction and proposed the Kitaev-off-diagonal (Κ-Γ) model to describe the material, and tuned the material into the QSL phase by applying magnetic field [Phys. Rev. Lett. 118, 107203 (2017); Phys. Rev. Lett. 119, 227208 (2017); Phys. Rev. Lett. 120, 067202 (2018)]. However, there has not been concrete evidence for the fractional excitations resulting from the Kitaev QSL state so far. In this work, we present the first polarized inelastic neutron scattering study on α-RuCl₃ single crystals to explore the scattering continuum around the Γ point at the Brillouin zone center and obtain evidence for the magnetic fractional excitations. We find that there exist pure continuous magnetic excitations near the Γ point, which are robust against temperature, as opposed to the spin waves near the Μ point that vanish above T_N. In addition, by comparing the calculation results using Κ-Γ and Kitaev–Heisenberg models with the unpolarized neutron experimental data, we find that the Κ-Γ model with a ferromagnetic Κ = −7.2 meV and a comparable Γ = 5.6 meV can reproduce not only the spin-wave excitations near the Μ point, but also the continuous excitations near the Γ point. These results are evident that there exist exotic fractional excitations in α-RuCl₃ due to its proximity to the Kitaev QSL state, and further support the Κ-Γ model to be the minimal effective spin model in describing the system. More details can be found here.

2021-12-29

Evidence for strong correlations at finite temperatures in the dimerized magnet Na2Cu2TeO6

Our group published a paper entitled “Evidence for strong correlations at finite temperatures in the dimerized magnet Na₂Cu₂TeO₆” in PRB [Phys. Rev. B 104, 224430 (2021)]. Dimerized magnets forming alternating Heisenberg chains exhibit quantum coherence and entanglement and thus can find potential applications in quantum information and computation. However, magnetic systems typically undergo thermal decoherence at finite temperatures. In this work, we report comprehensive inelastic neutron scattering (INS) measurements on a dimerized magnet Na₂Cu₂TeO₆, which is identified to be an alternating antiferromagnetic-ferromagnetic (AFM-FM) chain compound. We find that the excited quasiparticles in Na₂Cu₂TeO₆ can counter thermal decoherence and maintain strong correlations at elevated temperatures. At low temperatures, our INS excitation spectra clearly identify Na₂Cu₂TeO₆ to be an alternating AFM-FM chain compound with weak but nonzero interchain coupling. More importantly, we find the energy scans show asymmetric line shapes at elevated temperatures different from conventional magnets, which is a manifestation of a strongly correlated state resulting from hard-core constraint and quasiparticle interactions. These results serve not only as evidence for strong correlations at finite temperatures in Na₂Cu₂TeO₆, but also for the universality of the strongly correlated state in a broad range of quantum magnetic systems.

2021-07-05

Topological magnon insulator spin excitations in the two-dimensional ferromagnet CrBr3

Our group published a paper entitled “Topological magnon insulator spin excitations in the two-dimensional ferromagnet CrBr₃” as a Letter in PRB [Phys. Rev. B 102, L020402 (2021)]. Topological magnons are bosonic analogues of topological fermions in electronic systems. They have beenstudied extensively by theory but rarely realized by experiment. Here, by performing inelastic neutron scattering measurements on single crystals of a two-dimensional ferromagnet CrBr₃, which was classified as Dirac magnon semimetal featured by the linear bands crossing at the Dirac points, we fully map out the magnetic excitation spectra, and reveal that there is an apparent gap of ∼3.5 meV between the acoustic and optical branches of the magnons at the K point. By collaborative efforts between experiment and theoretical calculations using a five orbital Hubbard model obtained from first-principles calculations to derive the exchange parameters, we find that a Hamiltonian with Heisenberg exchange interactions, next-nearest-neighbor Dzyaloshinskii-Moriya (DM) interaction, and single-ion anisotropy is more appropriate to describe the system. Calculations using the model show that the lower and upper magnon bands separated by the gap exhibit Chern numbers of ±1. These results indicate that CrBr3 is a topological magnon insulator, where the nontrivial gap is a result of the DM interaction.

2021-06-17

Group members received "Outstanding Oral Presentation Award"!

Song Bao and Zhengwei Cai received "Outstanding Oral Presentation Award" in the 5th Jiangsu Physical Society Spring Conference, with talks entitled "Coexistence and interplay of itinerant and local moments in the van der Waals metallic ferromagnet Fe_3-xGeTe₂", and "Neutron Scattering and Transport Studies on Topological Magnon Insulator CrBr₃", respectively. Congratulations to them!

2021-06-06

​Congratulations to Song and Zhengwei for successfully defending their theses !

Song and Zhengwei successfully defended their PhD Theses on May 27th. Their outstanding works have been highly appreciated by the Defense Committee. They will be awarded the PhD degree soon. Congratulations, Dr. Bao and Dr. Cai! The group thank them for their great contributions and wish both of them a wonderful career!

2021-05-17

Prof. Wen was awarded "Jiangsu Distinguished Young Scholar in Physics"！

Jiangsu Physical Society (JSPS) awarded Prof. Wen "Jiangsu Distinguished Young Scholar in Physics" on July, 2020. Congratulations to him!

2021-01-08

Prof. Wen was awarded "Jiangsu Provincial Science and Technology Medal for Young Scientists"！

On January 7th, 2021, Prof. Wen received “Jiangsu Provincial Science and Technology Medal for Young Scientists " for his accomplishment in cutting-edge research in experimental condensed matter physics, dedication in teaching and educating students, and contributions to the public service. Congratulations to him! More details can be found here.

2020-12-24

Prof. Wen received the honor of "My Favorite Supervisor in Graduate Career"！

Prof. Wen was honorably named as "My Favorite Supervisor in Graduate Career" by the unversity for his dedication and excellency in supervising graduate students. Congratulations to him!

2020-12-16

Disorder-induced spin-liquid-like behavior in kagome-lattice compounds

Our group published a paper entitled “Disorder-induced spin-liquid-like behavior in kagome-lattice compounds” in PRB [Phys. Rev. B 102, 224415 (2020)]. Quantum spin liquids (QSLs) are a novel state of matter that is subject to extensive research. However, the relationship between the ubiquitous disorder and the QSL behaviors is still unclear. In this work, to identify the role of disorder in the QSL candidates, we choose Tm₃Sb₃Zn₂O₁₄ and its sister compound Tm₃Sb₃Mg₂O₁₄ with quantifiable disorder, that is, strong and weak disorder in the former and latter, respectively, and investigate how disorder affects the material’s magnetic properties. The comparative and comprehensive experimental studies with magnetic susceptibility, ultralow-temperature specific heat, and inelastic neutron scattering (INS) show spin-liquid-like features in both compounds. However, we find in Tm₃Sb₃Zn₂O₁₄, which has strong disorder resulting from the random mixing of the magnetic Tm³⁺ and nonmagnetic Zn²⁺, that the low-energy magnetic excitations observed in the specific heat and INS measurements are substantially enhanced compared to those of Tm₃Sb₃Mg₂O₁₄, which has much less disorder. We believe that the effective spins of the Tm³⁺ ions in the Zn²⁺/Mg²⁺ sites give rise to the low-energy magnetic excitations, and the amount of the random occupancy determines the excitation strength. These results provide direct evidence of the mimicry of a QSL caused by disorder.

2020-11-06

Evidence of the Berezinskii-Kosterlitz-Thouless Phase in a frustrated magnet

Our group published a paper entitled “Evidence of the Berezinskii-Kosterlitz-Thouless Phase in a frustrated magnet” in Nature Communications [Nat. Commun. 11, 5631 (2020)] in collaboration with Prof. Weiqiang Yu’s group at RUC, Prof. Wei Li’s group at Beihang, Prof. Ziyang Meng’s group at HKU/IOP, and Prof. Yang Qi at Fudan. The Berezinskii-Kosterlitz-Thouless (BKT) mechanism, one of the main contributions leading to the Nobel Prize in Physics 2016 for “theoretical discoveries of topological phase transitions and topological phases of matter”, was proposed in 2D magnetic systems in early 1970s by two of the Nobel laureates (together with late Vadim Berezinskii) whom the mechanism was named after. It constitutes the first example of topological phase transition beyond the Landau-Ginzburg paradigm of order parameter and symmetry breaking. Such a topological phase transition has long been sought yet undiscovered directly in magnetic materials. In this work, we pin down two transitions that bound a BKT phase in an ideal 2D frustrated magnet TmMgGaO₄, via nuclear magnetic resonance under in-plane magnetic fields, which do not disturb the low-energy electronic states and allow BKT fluctuations to be detected sensitively. Moreover, by applying out-of-plane fields, we find a critical scaling behavior of the magnetic susceptibility expected for the BKT transition. The experimental findings can be explained by quantum Monte Carlo simulations applied on an accurate triangular-lattice Ising model of the compound which hosts a BKT phase. These results provide a concrete example for the BKT phase and offer an ideal platform for future investigations on the BKT physics in magnetic materials. More details can be found here.

2020-08-26

Group members awarded for "Excellent Doctoral Thesis"!

Kejing Ran and Jinghui Wang, both graduated from our group in 2019, have been awarded "Excellent Doctoral Thesis" by the University, with Theses entitled "Neutron Scattering Investigations on a Kitaev Quantum Spin Liquid Candidate α-RuCl₃", and "Neutron Scattering Study on Unconventional Superconductors", respectively.  As their advisor, Prof. Wen was awarded  "Advisor of Excellent Doctoral Thesis" accordingly. Congratulations to them and the group!

2020-07-22

Congratulations to Yuan and Zhen for successfully defending their theses !

Yuan and Zhen successfully defended their PhD Theses on July 21st. Their outstanding works have been highly appreciated by the Defense Committee. They will be awarded the PhD degree soon. Congratulations, Dr. Gan and Dr. Ma! The group thank them for their great contributions and wish both of them a wonderful career!

2020-06-12

Evidence for magnon-phonon coupling in the topological magnet Cu3TeO6

Our group published a paper entitled "Evidence for magnon-phonon coupling in the topological magnet Cu₃TeO₆" in PRB [Phys. Rev. B 101, 214419 (2020)]. In this work, we report comprehensive results of thermodynamic and inelastic neutron scattering (INS) measurements on a cubic collinear antiferromagnet Cu₃TeO₆, which hosts topological magnons. We find the measured thermal conductivity deviates from a pure phononic model, indicating that there is a strong coupling between magnons and phonons. Our INS measurements find an additional mode located at about 16.8 meV, which exhibits a slight downward dispersion around the zone center and disappears above the T_N. The dispersion and temperature dependence of this mode is inconsistent with it being either a pure magnon or a phonon. Instead, we attribute it to a magnon-polaron mode, collective excitations resulting from the hybridization between magnons and phonons. We consider the suppression of thermal conductivity and the emergence of the magnon-polaron mode to be evidence for magnon-phonon coupling in Cu₃TeO₆. Our work shows that Cu₃TeO₆ provides a rare platform to investigate the interplay between topological magnons and phonons in a three-dimensional collinear antiferromagnetic case.

2020-04-08

Spin dynamics of a magnetic Weyl semimetal Sr1−xMn1−ySb2

Our group published a paper entitled "Spin dynamics of a magnetic Weyl semimetal Sr_1−xMn_1−ySb₂" in PRB [Physical Review B 101, 134408 (2020)]. In this work, we report comprehensive inelastic neutron scattering measurements (INS) on single crystals of Sr_1−xMn_1−ySb₂, which have been well characterized by magnetization and magnetotransport measurements, both of which demonstrate that the material is a topologically nontrivial semimetal. The INS spectra can be well described by a localized Heisenberg model with SJ₁ ∼ 28.0 meV, SJ₂ ∼ 9.3 meV, a small SJ_c ∼ −0.1 meV, and SD ∼ −0.07 meV. Despite the coexistence of Weyl fermions and magnons, we find no clear evidence that the magnetic dynamics are influenced by the Weyl fermions in this material, possibly because that the Weyl fermions and magnons reside in separated layers, and the interlayer coupling is weak due to the quasi-two-dimensional nature of the material.

2019-06-27

Evidence for singular-phonon-induced nematic superconductivity in Sr0.1Bi2Se3

Our group published a paper entitled "Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr_0.1Bi₂Se₃" in Nature Communications [Nat. Commun. 10, 2802 (2019)]. In this work, by performing inelastic neutron scattering measurements on a superconducting single crystal of Sr_0.1Bi₂Se₃, a prime candidate for realizing topological superconductivity, we find that there exist highly anisotropic phonons, with the linewidths of the acoustic phonons increasing substantially at long wavelengths, but only for those along the [001] direction. This observation indicates a large and singular electron-phonon coupling at small momenta, which we propose to give rise to the exotic p-wave nematic superconducting pairing. Therefore, we show M_xBi₂Se₃ (M = Cu, Sr, Nb) to be example systems where electron-phonon interaction can induce more exotic superconducting pairing than the s-wave, consistent with the topological superconductivity. More details can be found here.

2019-05-20

Congratulations to Kejing and Jinghui for successfully defending their theses !

Kejing and Jinghui successfully defended their PhD Theses on May 20th. Their outstanding works have been highly appreciated by the Defense Committee. They will be awarded the PhD degree soon. They continue their further research at ShanghaiTech University. Congratulations, Dr. Ran and Dr. Wang! The group thank them for their great contributions and wish both of them a wonderful career!

2019-04-08

Review article published in npj Quantum Materials

In collaboration with other four professors Shun-Li Yu, Shiyan Li, Weiqiang Yu and Jian-Xin Li, Prof. Jinsheng Wen published a review paper entitled "Experimental identification of quantum spin liquids" in npj Quantum Materials [npj Quantum Materials 4, 12 (2019)]. In this review paper, interesting experimental developments are highlighted, outstanding issues are discussed, and questions that are considered to be important for future research are raised. 

2018-11-08

Congratulations to Kejing for the Special Prize of Baosteel!

Kejing Ran has been awarded the "Special Prize of Baosteel" of the year 2018.  Congratulations to her! More details can be found here.

2018-10-12

Paper published in Nanoletters in collaboration with Prof. Shao-chun Li's group

In collaboration with Prof. Shao-chun Li's group in our Department, we published a paper entitled "Superconductivity in Potassium-Intercalated T_d-WTe₂" in Nanoletters  [Nano Lett. 18, 6585-6590 (2018)]. In this study, we discover the superconducting state in K-intercalated WTe₂through both electrical transport and scanning tunneling spectroscopy measurements. The results suggest that K_xWTe₂ may be a promising candidate to explore the topological superconductor. More details can be found here.

2018-09-16

Congratulations to Song for the Best Poster Prize at the CPS Fall Meeting!

Song Bao has been awarded the "Best Poster Prize" at the 2018 Chinese Physical Society Fall Meeting held in Dalian. Congratulations to him!

2018-07-04

Discovery of topological magnons in a three-dimensional antiferromagnet

Our group discover an exotic topological state of matter---coexisting Dirac and triply degenerate magnons in a three-dimensional antiferromagnet Cu₃TeO₆. The work was published in Nature Communications [Nat. Commun. 9, 2591 (2018)]. Analogous to topological electronic systems, such as topological insulators, and Dirac/Weyl semimetals, topological magnonic systems exhibit fascinating topological properties which may enable high-efficiency and low-cost spintronic devices. Experimental realization of topological magnons in three dimensions has not been reported so far. In our work, we measure the spin excitations in Cu₃TeO₆ with inelastic neutron scattering (INS), and compare the INS data with the linear-spin-wave calculations. From the results, we discover symmetry-protected three-dimensional Dirac and triply degenerate magnons in Cu₃TeO₆, the latter beyond the Dirac-Weyl framework. Our work showcases Cu₃TeO₆ as the first example where Dirac and triply degenerate magnonic excitations coexist, demonstrate a topological state of matter that has never been perceived before, and provide an entirely fresh ground to explore the topological properties in quantum materials.  More details can be found here.

2018-06-17

Unusual response to the superconducting transition in an In-doped topological crystalline insulator

Our group published a paper entitled "Unusual phonon density of states and response to the superconducting transition in the In-doped topological crystalline insulator Pb_0.5Sn_0.5Te" in PRB as a Rapid Communication [Physical Review B 97, 220502(R) (2018)]. In this work, we observe unexpected van Hove singularities in the phonon density of states at energies of 1–2.5 meV. We also observe that, when the superconducting sample is cooled below the superconducting transition temperature T_c, an enhancement of the phonon density of states with energies below twice the superconducting-gap energy. Our results suggest that while the superconductivity in the In-doped (Pb_0.5Sn_0.5)Te sample is driven by phonons, its superconducting mechanism is beyond a simple BCS theory.

2018-05-17

Evidence for a Dirac nodal-line semimetal in SrAs3

Our group published a paper titled "Evidence for a Dirac nodal-line semimetal in SrAs₃" in Science Bulletin [Li et al., Science Bulletin 63, 535 (2018)]. By carrying out magnetotransport measurements and performing first-principle calculations, we demonstrate that the topological Dirac nodal-line state has been realized in high-quality single crystals of SrAs₃. We obtain the nontrivial π Berry phase by analysing the Shubnikov-de Haas quantum oscillations. We also observe a robust negative longitudinal magnetoresistance induced by the chiral anomaly. Accompanying first-principles calculations identify that a single hole pocket enclosing the loop nodes is responsible for these observation.

2018-02-23

Our group published a fourth paper in PRL on quantum spin liquid candidates

In collaboration with Prof. Jian-Xin Li's group in our department and Shiyan Li's group in Fudan University, we published a paper entitled "Spin-Glass Ground State in a Triangular-Lattice Compound YbZnGaO₄" in PRL  [PRL 120, 087201 (2018)]. YbMgGaO₄ has attracted a lot of attention in recent years due to the possibility of realizing the exotic quantum-spin-liquid (QSL) ground state. However, by studying its sister compound YbZnGaO₄ with various techniques including dc susceptibility, ultralow-temperature specific heat, inelastic neutron scattering, ultralow-temperature thermal conductivity and ac susceptibility, combined with linear spin-wave calculations, we find that the material is not a QSL, but instead a spin glass, with frozen, short-range spin-spin correlations at low temperatures. This conclusion also holds for YbMgGaO₄, as confirmed by the ultralow-temperature ac susceptibility measurements. Our work provides an important lesson in identifying a QSL, as disorder-induced spin glass mimics it in many aspects. More details can be found here.

2018-02-10

Our group's third PRL paper on α-RuCl3

In collaboration with Prof. Shiyan Li's group in Fudan University, we published a paper titled "Ultralow-Temperature Thermal Conductivity of the Kitaev Honeycomb Magnet α-RuCl₃ across the Field-Induced Phase Transition" in  [PRL 120, 067202 (2018)]. This is our group's third PRL paper on α-RuCl₃ within one year. Previously, we demonstrated that the Kitaev physics is realized in α-RuCl₃ [ PRL 118, 107203 (2017)] (see also, the News), and a quantum spin liquid phase may be induced by an external magnetic field   [PRL 119, 227208 (2017)] (see also, the News). In this work, we further investigate the high-field phase by performing ultralow-temperature thermal conductivity measurements on single crystals of α-RuCl₃. We provide key insights into the field-induced phase and strong constrains for the theory. More details can be found  here.

2017-12-04

Congratulations to Shichao for successfully defending his thesis !

Shichao successfully defended his PhD Thesis on December 4th. His sustained efforts have been highly appreciated by the Defense Committee. He will be awarded the PhD degree soon and become the first PhD graduated from our group. Congratulations, Dr. Li! The group thank him for his great contributions and wish him a wonderful career!

2017-12-02

Our group made another important discovery in α-RuCl3

In collaboration with Prof. Weiqiang Yu's group in Renmin University of China, we published a paper titled "Gapless Spin Excitations in the Field-Induced Quantum Spin Liquid Phase of α-RuCl₃" in   [PRL 119, 227208 (2017)].   α-RuCl₃ is a leading candidate to realize the Kitaev physics, as we demonstrated earlier in [ PRL 118, 107203 (2017)] (see also, the News). In this work, we combined susceptibility, specific-heat, and nuclear-magnetic-resonance measurements, showing that α-RuCl₃ becomes a quantum spin liquid in a magnetic field of 7.5 T applied in the a-b plane. More details can be found here.

2017-11-27

Paper published in PRB in collaboration with Prof. Weiqiang Yu's group

In collaboration with Prof. Weiqiang Yu 's group in Renmin University of China, our group coauthored a paper in Physical Review B 96, 205147 (2017), reporting high-pressure magnetization and NMR studies of a proximate quantum spin liquid candidate α-RuCl₃. In this work, Kejing provided the high-quality single crystals.

2017-11-01

Congratulations to Zhen for the "Excellent Paper Prize for Young Scholars" on the China Neutron Scattering Conference!

Zhen Ma has been awarded the "Excellent Paper Prize for Young Scholars" on the 5th China Neutron Scattering Conference held in Chengdu. Congratulations to him!

2017-09-10

Interplay between superconductivity and antiferromagnetic order in KxFe2-ySe2

Our group published a paper titled "Suppression of the antiferromagnetic order when approaching the superconducting state in a phase-separated crystal of K_xFe_2-ySe₂"  on PRB [Li et al., Physical Review B 96, 094503 (2017)]. In this work, we  observe both the spin-wave excitations and spin resonance, resulting from the antiferromagnetic and superconducting phases, respectively.  We find that well before entering the superconducting state, the development of the magnetic order is interrupted, at ∼ 42 K. We consider this result to be evidence for the physical separation of the antiferromagnetic and superconducting phases. More details can be found here.

2017-03-01

Our group published a paper in PRL in collaboration with Prof. Jian-Xin Li's group, reporting the finding of Kitaev physics in α-RuCl3

We reported the key ingredient composing Kitaev's proposal in a paper titled "Spin-Wave Excitations Evidencing the Kitaev Interaction in Single Crystalline α-RuCl3" in PRL [Ran et al., Physical Review Letters 118, 107203 (2017)]. The celebrated Kitaev quantum spin liquid was proposed theoretically in the year of 2006. This new state exhibits exotic properties in which electrons are broken into pieces, and it can find applications in quantum computation. Experimentally, such a state has not been identified so far. In our work, we have found that the behaviors of the spins in single crystals of a honeycomb-layered material RuCl₃ fit Kitaev's proposal well. Our results demonstrate that the Kitaev interaction, the concept central to the proposal, has been discovered in a real material. These findings pave the way for further harnessing the material for quantum computation. More details can be found here.

2017-02-20

Paper published in Nature Communications in collaboration with Prof. Haihu Wen's group

In collaboration with Prof. Haihu Wen's group in our Department, our group coauthored a paper in Nature Communications 8, 14466 (2017), reporting interesting behaviors of the superconducting state in a promising candidate for topological superconductivity in Sr_xBi₂Se₃. In this work, Jinghui and Kejing provided very high-quality single crystals of Sr_xBi₂Se₃. A more detailed news report can be found here.

2016-12-24

Prof. Wen delivered a lecture on neutron sca-ttering studies on high-Tc superconductors at PLAUST

Prof. Wen has been invited to give a lecture at PLAUST (PLA University of Science and Technology) on Dec. 24th, introducing neutron scattering techniques and studies on high-Tc superconductors. This activity is organized by PLAUST and Jiangsu Society of Physcis, more details can be found here. 

2015-06-02

Papers published as tributes to the Centenary of our Physics Department

Our group published a paper titled "Magnetic neutron scattering studies on the Fe-based superconductor system Fe_1+yTe_1-xSe_x" on  Annals of Physics as a tribute to the centenary of our Physics Department. The Chinese version of the article was published on Acta Physics Sinica. In this paper, we present a brief overview on the interplay between magnetism and superconductivity in one of the Fe-based superconductor systems, Fe_1+yTe_1-xSe_x. We conclude that magnetism and superconductivity in this system couple to each other closely, while the static magnetic order around (0.5, 0) competes with superconductivity, the spin excitations around (0.5, 0.5) may be an important ingredient for it. We also discuss the nature of magnetism and substitution effects of 3d transition metals.

2015-01-15

Floating-zone furnace ready for use

A floating-zone furnace has been installed at our lab and is ready for use. It is equipped with two ellipsoidal mirrors, which reflect light emitted from two Halogen lamps to melt the raw materials. The melted zone is held by surface tension only, and for this reason this technique is termed "floating-zone" technique. Crystal growth is initiated by a slow downward translation of the feed rod mounted on the upper shaft and the seed rod on the lower shaft. It is suitable for growing precisely controlled stoichiometry single crystals with high melting point (can reach above 2000 ^。C), for example, high-temperature cuprate superconductors.

2015-01-06

Effects of 3d transition metal substitution in the Fe-based superconductors

Our group published a paper titled "Substitution of Ni for Fe in superconducting Fe_0.98Te_0.5Se_0.5 depresses the normal-state conductivity but not the magnetic spectral weight" on PRB. In this work, we study the Ni-substitution effects on the electronic and magnetic properties of an Fe-based superconductor Fe_0.98Te_0.5Se_0.5. Together with our previous paper on the Cu-doping effects [PRB 88, 144509 (2013)], we provide a complete picture on the 3d transition metal substitution effects in the Fe-based superconductors---that is, the impact is more depe ndent on the scattering potential of the substituent, and in the extreme case such as Cu, the main effect of the substitution is to localize the itinerant electrons. This conclusion also seems to be applicable to other Fe-based superconductor systems, such as 122 and 111. Jinghui has been the leading author of the paper. This is his first paper. Congratulations on him!

2014-12-24

Congratulations on Jinghui and Kejing for their scholarships!

Jinghui Wang and Kejing Ran have been awarded the "Excellent New Graduate Student Scholarship". Congratulations to them!

2014-10-25

PPMS installed and running

The physical property measurement system (PPMS) was installed at our lab and is currently running. It is using a closed-cycle system with a compressor that converts Helium gas into liquid He, and thus no liquid He supply is needed at all. The system is equipped with the options to measure the magnetization (VSM), electrical transport (ETO), thermal power and conductivity (TTO), and specific heat (HCO).

2014-06-25

Group members graduated!

Three of our undergraduate group members, Zhonghan, Tao, and Jinghui have successfully defended their theses and obtained their bachelor's degree. They have made great achievements in the past four years. Congratulations to them! All of them will go to graduate schools: Zhonghan to National University of Singapore, Tao to Institute of High Energy Physics, and Jinghui at our group. Wish all of them a wonderful career!

2014-03-30

Experiments in France and U.S.

From Feburary 10th to 24th, Shichao conducted his first neutron scattering experiment at Laboratory of Leon Brillouin (LLB), CEA, a reactor-type neutron source at Saclay near Paris. He worked on two triple-axis spectrometers 1T and 2T.

During March 12th to 21st, Yuan and Jinghui  performed their first neutron scattering experiment on a triple-axis spectrometer HB1 at the High Flux Isotope Reactor (HFIR) of Oak Ridge National Lab.

2014-01-20

Dr. Zhang of UC Berkeley visited us

Dr. Wentao Zhang of UC Berkeley visited our lab, the department and the National Lab from January 14 to 15. He gave a talk titled "Signatures of superconductivity and pseudogap formation in non-equilibrium nodal quasiparticles revealed by ultrafast angle-resolved photoemission", detailing cuprate high-temperature superconductors, and angle-resolved photoemission spectroscopy (ARPES), and presenting his very nice recent work using time-resolved ARPES to study the high-temperature superconductor system Bi₂Sr₂CaCu₂O₈. His talk was well received by the audiences and stimulated many questions and discussions. He had discussions with our dean and other faculties after the talk.

2013-12-25

Happy Holidays!

Merry Christmas and Happy New Year to all! Wish all have wonderful holidays and a happy 2014!

2013-12-24

Our group website is launched!

Thanks to Jinghui and Tao's substantial efforts, our group website has been made possible. Jinghui built up the infrastructure and Tao input the data. For any questions on the website, please contact Prof. Wen at jwen@nju.edu.cn, or Jinghui at 402784407@qq.com.

2013-12-12

China Neutron Scattering Conference

Prof. Wen and Shichao attended the First China Neutron Scattering Conference in Dongguan, Guangdong, where the China Spallation Neutron Source (CSNS) is being built. Prof. Wen gave an invited talk advertising the group and presenting the research results. Shichao toured the construction site of the CSNS.

2013-12-07

Congratulations on Yuan for his scholarship!

Yuan Gan has been awarded the "Excellent New Graduate Student Scholarship". Congratulations on him!

2013-11-25

Group toured Qixia Mountain.

Our group went for a tour to Qixia Mountain on November 23.              We brought our own food and had a barbecue, and then we hiked        through the mountain. It provided an opportunity for the group members to have free discussions with each other and know each other better. Hope everyone enjoyed it. If you wan to see more photos, you can go to our photo album.

2013-11-01

Welcome to our group members!

Our group has been growing rapidly. Currently we have 13 members, including the PI, 2 graduate students, and 10 undergrates (two of them will become graduate students in the group next year). Wish all have a wonderful life and bright career.

2013-10-28

Dr. Tranquada of Brookhaven visited us.

Senior Physicist of Brookhaven National Laboratory, Dr. John M. Tranquada visited our group, the Physics Department and the National Lab from October 27 to 30. He gave a "Zhongshan Distinguished Lecture" titled "Superconductivity Intertwined with Antiferromagnetism" to the Department and the National Lab.        He had intensive discussions with our faculties and students. For those who are interested in knowing more details about his talk, here is a copy of the slides.

2013-10-27

Prof. Wen attended a symposium in Beijing.

Prof. Wen attended the "International Symposium on Frontier of Superconductivity Research (III)" with focus on "Neutron Scattering on Unconventional Superconductors" from October 24 to 27 organized by Institute of Physics in Beijing. He gave an invited talk titled "Magnetic excitations in Cu-doped Fe_0.98Te_0.5Se_0.5", describing our neutron scattering work on the Fe-based superconductors. He exchanged ideas and thoughts through discussions with the experts in the symposium.

2013-10-21

Our group published a paper on PRB.

We published a paper titled "Enhanced low-energy magnetic excitations via suppression of the itinerancy in Fe_0.98−zCu_zTe_0.5Se_0.5" on PRB. In this paper, we describe an unexpected observation that the low-energy magnetic excitations are enhanced by the Cu doping. Our results indicate that the rigid band model cannot be applied to our case. This is our first paper published using Nanjing University as the institution. Shichao is the 2nd author of it.

2013-10-16

Wen attended the Xiangshan Conference.

Prof. Wen attended the Xiangshan Science Conference from October 15 to 16 in Beijing. This workshop emphasized the great importance of neutron scattering and the immediate need of the neutron sources in China. It was aiming to help make better use of the built neutron sources and developing new ones.

2013-09-16

Prof. Wen attended a meeting in Xiamen.

Prof. Wen attended the "2013 Chinese Physical Society's Fall Meeting" held in Xiamen University. He advertised the group, gave an invited talk describing results from the group and had intensive discussions with attendees.