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 Pb0.5Sn0.5Te" 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 Tc, 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 (Pb0.5Sn0.5)Te sample is driven by phonons, its superconducting mechanism is beyond a simple BCS theory.



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.



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.



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.



Congratulations on Shichao for successfully defending his thesis !


Shichao successfully defended for 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!




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.




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.



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 KxFe2-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.



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.


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 SrxBi2Se3. In this work, Jinghui and Kejing provided very high-quality single crystals of SrxBi2Se3. A more detailed news report can be found here.


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


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 Fe1+yTe1-xSex" 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, Fe1+yTe1-xSex. 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.


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.


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


Our group published a paper titled "Substitution of Ni for Fe in superconducting Fe0.98Te0.5Se0.5 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 Fe0.98Te0.5Se0.5. 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!


Congratulations on Jinghui and Kejing for their scholarships!


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


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).


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!


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.


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.


Happy Holidays!


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


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, or Jinghui at


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.


Congratulations on Yuan for his scholarship!


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


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.


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.


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.


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 Fe0.98Te0.5Se0.5", describing our neutron scattering work on the Fe-based superconductors. He exchanged ideas and thoughts through discussions with the experts in the symposium.


Our group published a paper on PRB.


We published a paper titled "Enhanced low-energy magnetic excitations via suppression of the itinerancy in Fe0.98−zCuzTe0.5Se0.5" 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.


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.


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.