2026-08-26

Ligand-Driven Kitaev Interactions in NiI2—PRB Letter Selected as Editors' Suggestion

Our group has published a Letter entitled "Sizable ligand-mediated bond-dependent interactions in the spin-1 triangular antiferromagnet NiI₂" in Physical Review B [Phys. Rev. B 114, L080405 (2026)], which was selected as an Editors’ Suggestion. This work was carried out in collaboration with Professor Changsong Xu's group at Fudan University.

Bond-dependent anisotropic Kitaev interactions are central to Kitaev physics and may give rise to quantum spin liquids and fractional excitations. However, experimentally established realizations remain scarce, particularly in high-spin systems. NiI₂ is a layered van der Waals magnet in which spin-1 Ni²⁺ ions form a triangular lattice. Because the orbital angular momentum of Ni²⁺ is quenched and iodine ions could provide a strong spin-orbit coupling, NiI₂ provides an ideal platform for testing whether strong spin-orbit coupling on heavy ligand ions can instead generate sizable Kitaev interactions. By combining inelastic neutron scattering measurements on single crystals with magnetization measurements, magnetic structure analysis, first-principles calculations, and linear-spin-wave simulations, we establish a minimal magnetic Hamiltonian containing sizable Kitaev and off-diagonal Γ interactions. These bond-dependent interactions stabilize the canted proper-screw magnetic ground state and account for the 3.1-meV gap observed in the spin-wave spectrum. The optimal model yields a Kitaev interaction of 3.33 meV and successfully reproduces the experimentally observed canting angle and incommensurate magnetic period.

This work provides compelling experimental evidence for a ligand-driven Kitaev mechanism: substantial bond-dependent anisotropic interactions can emerge from strong spin-orbit coupling on ligand ions even when the orbital moment of the magnetic ions is quenched. The results establish triangular-lattice NiI₂ as an important high-spin platform for exploring Kitaev physics and provide a concrete pathway for identifying Kitaev interactions in a much broader class of magnetic materials.

2026-07-20

Paper on Na3Ni2BiO6 published in Nature Communications

Our group has published a paper entitled “Cascade of magnetic-field-induced quantum spin states in a spin-1 honeycomb magnet” in Nature Communications [Nat. Commun. 17, 6669 (2026)], in collaboration with Prof. Jian-Xin Li’s group at our School of Physics, as well as Prof. Ziji Xiang and Prof. Xianhui Chen’s group at the University of Science and Technology of China.

Building upon our previous work published in Nature Physics [Nat. Phys. 19, 1883 (2023)], where a one-third magnetization plateau was identified as a hallmark of Kitaev interactions in Na₃Ni₂BiO₆, the present study further explores the rich magnetic phase diagram of this spin-1 honeycomb magnet under applied magnetic fields. Quantum fluctuations can profoundly enrich the phase diagrams of spin systems. In frustrated magnets, such fluctuations—enhanced by either geometrical incompatibility or competing exchange interactions—can stabilize cascades of unconventional phases. In this work, we reveal multiple quantum phases in the honeycomb antiferromagnet Na₃Ni₂BiO₆, both within and beyond its field-induced one-third magnetization plateau. Comprehensive thermodynamic measurements show that the plateau regime itself hosts at least three distinct spin states with nearly degenerate magnetization, separated by first-order transitions that likely involve successive spin reconfigurations. Upon further increasing the magnetic field, the system evolves through a series of additional intermediate phases before reaching full polarization. These phases exhibit abundant low-energy excitations, as evidenced by anomalous upturns in the specific heat at ultralow temperatures, suggesting the emergence of possible “hidden” ordered ground states. The complex magnetic phase diagram revealed in this work highlights the crucial role of quantum fluctuations in a honeycomb spin lattice with strong exchange frustration, and provides new insights into emergent quantum states in high-spin Kitaev materials. 

2026-05-22

Celebrating Scholarly Excellence: Dr. Zhang Bo Successfully Defends Doctoral Dissertation

We are proud to celebrate the successful Ph.D. thesis defense of the outstanding member of our research group, Dr. Bo Zhang, on May 20th.

Throughout his doctoral studies, Dr. Zhang has shown remarkable dedication and insight in the study of magnetic Weyl semimetals. Combining advanced neutron scattering and elaborate electric transport measurements, he has greatly enriched his scientific perspective. With a meticulous approach and a keen eye for subtle details, he excels at uncovering hidden phenomena.

Please join us in congratulating Dr. Zhang on this remarkable accomplishment. We look forward to his continued contributions to the advancement of science.

2026-04-17

Magnon Damping Reveals Kondo Physics in a d-Electron Ferromagnet

Our group has published a paper entitled "Magnon Damping as a Probe of Kondo Coupling in Magnetically Ordered Systems" in Nature Communications [Nat. Commun. 17, 3557 (2026)].

The interplay between Kondo coupling and magnetic interactions can produce a wide range of emergent phenomena---including magnetism, heavy-fermion behavior, strange-metal states, superconductivity, and quantum criticality---making it a central topic in condensed matter physics. While most studies have focused on f-electron systems, experimental investigations in d-electron materials remain rare. Moreover, signatures of the Kondo effect have traditionally been identified through transport, thermodynamic, or electronic band measurements, whereas direct probes via spin excitation spectra are largely unexplored. Using inelastic neutron scattering, here we report direct measurement of momentum-resolved damping of collective spin excitations in a metallic ferromagnet Fe_3-xGeTe₂, which we show to exhibit the coexistence of itinerant electrons and local moments as well as possible Kondo coupling in a previous work [Phys. Rev. X 12, 011022 (2022)]. We find that magnon damping diverges at both low and high temperatures and shows a pronounced minimum at an intermediate temperature. This behavior is well captured by a formula combining logarithmic and power-law terms, reflecting contributions from Kondo coupling and thermal fluctuations, respectively. State-of-the-art tensor-network calculations of a ferromagnetic Kondo-Heisenberg lattice model reproduce the observations and reveal a new mechanism of Kondo-coupling induced magnon-electron scattering.

This work extends Kondo physics from isolated spins to collective spin excitations and establishes a new spectroscopic route to detect Kondo coupling in magnetically ordered systems. More details can be found here.

2026-03-02

Magnetic Signatures of Chiral Phonons Observed via Neutron Scattering---PRL Paper Selected as Editors' Suggestion and Featured in Physics

Our group has published a paper entitled "Magnetic Signature of Chiral Phonons Revealed by Neutron Spectroscopy in Ferrimagnetic Fe_1.75Zn_0.25Mo₃O₈" in Physical Review Letters [Phys. Rev. Lett. 136, 096502 (2026)]. The paper was selected as an Editors' Suggestion and featured in Physics magazine [Physics 19, 28 (2026)].

Chiral phonons, characterized by circularly polarized ionic motions that carry angular momentum and associated phonon magnetic moments, have recently emerged as a new frontier in condensed matter physics. They are expected to enable novel phenomena such as phonon magnetism and the phonon Hall effect. However, because ions are much heavier than electrons, the orbital magnetic moments generated by ionic cyclotron motion are typically very small, leading to extremely weak magnetic scattering. This has made the direct experimental detection of chiral phonons, particularly by techniques such as inelastic neutron scattering, highly challenging. In this work, we report the direct neutron detection and energy-momentum-resolved mapping of the magnetic signatures of chiral phonons in the ferrimagnetic compound Fe_1.75Zn_0.25Mo₃O₈, a system featuring strong magnon-phonon coupling and hybrid excitations as we demonstrated in our previous series of work  [Nat. Commun. 14, 6093 (2023), Nat. Phys. 19, 1868 (2023), Phys. Rev. Lett. 134, 236701 (2025)]. Below the magnetic ordering temperature, the phonon spectra exhibit significantly enhanced magnetic scattering, accompanied by out-of-plane intensity modulation, intrinsic mode splitting, and field-induced Zeeman shifts. These observations demonstrate that the phonons carry substantial magnetic moments and exhibit chiral character. 

This work provides the first direct observation of chiral-phonon dispersions across the full energy-momentum space using neutron spectroscopy, reveals magnetic scattering signatures of chiral phonons that are distinct from nuclear scattering in the magnetically ordered state, deepens the understanding of chiral phonons, and opens a new avenue for probing phonon magnetism with neutron scattering. Professor Yuan Wan of Institute of Physics wrote a viewpoint about this work in Physics entitled "Neutrons Illuminate the Magnetic Dance of Chiral Phonons". He commended the work as "By revealing this elaborate choreography (behaviors of chiral phonons) in a magnetic crystal, they have opened the door to testing theoretical models and developing practical applications". More details can be found here.

2026-01-30

Magnetic anisotropy and spin-disordered ground state in the triangular-lattice antiferromagnet K2CsYb(PO4)2

Our group, in collaboration with the group led by our alumni Professor Zhen Ma at Hubei Normal University, published a paper titled “Magnetic anisotropy and spin-disordered ground state in the triangular-lattice antiferromagnet K₂CsYb(PO₄)₂” in Physical Review B [Phys. Rev. B 113, 035157 (2026)].

Triangular-lattice antiferromagnets are prototypical geometrically frustrated systems capable of hosting diverse quantum states, including quantum spin liquids (QSLs) which are of particular interest. However, intrinsic structural disorder in real candidate materials often complicates the picture and can lead to spin-glass behavior instead. In this study, we successfully synthesized single crystals of a new rare-earth triangular-lattice compound, K₂CsYb(PO₄)₂. X-ray diffraction confirms high phase purity with no detectable structural disorder. DC magnetic susceptibility measurements reveal dominant magnetic anisotropy, with a stronger magnetic response within the ab-plane compared to along the c-axis. Notably, no magnetic phase transition or spin freezing is observed down to 400 mK, a result further supported by AC susceptibility measurements. Moreover, specific heat measurements down to 50 mK show no signature of long-range magnetic order, but instead exhibit a Schottky anomaly well described by a two-level system. These data point to a spin-disordered ground state with quantum spin liquid behavior. Complementary first-principles calculations based on density functional theory establish a spin-orbit entangled ground state with an effective spin J_eff = 1/2. Together, these results establish K₂CsYb(PO₄)₂---a compound with perfect triangular lattice as an ideal platform for exploring quantum magnetism.

2025-12-31

Happy New Year!

Happy New Year 2026!

May this year be abundant in harvests, rich in achievements, smooth in journeys, and bright with hope.

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.