Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation,but also is helpful for furthe...Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation,but also is helpful for further understanding the heavy fermion superconductivity.Here we report a low-temperature and vector-magneticfield scanning tunneling microscopy and spectroscopy study on a superconducting compound(4Hb-TaS_(2))with alternate stacking of 1T-TaS_(2)and 1H-TaS_(2)layers.We observe the quasi-two-dimensional superconductivity in the 1H-TaS_(2)layer with anisotropic response to the in-plane and out-of-plane magnetic fields.In the 1T-TaS_(2)layer,we detect the Kondo resonance peak that results from the Kondo screening of the unpaired electrons in the Star-of-David clusters.We also find that the intensity of the Kondo resonance peak is sensitive to its relative position with the Fermi level,and it can be significantly enhanced when it is further shifted towards the Fermi level by evaporating Pb atoms onto the 1T-TaS_(2)surface.Our results not only are important for fully understanding the electronic properties of 4Hb-TaS_(2),but also pave the way for creating tunable Kondo lattice in the superconducting van der Waals materials.展开更多
It is known that α-RuCl_(3) has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid(QSL)phase and the possibility of approaching it by tuning the competing interactions.Here we present...It is known that α-RuCl_(3) has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid(QSL)phase and the possibility of approaching it by tuning the competing interactions.Here we present the first polarized inelastic neutron scattering study on α-RuCl_(3) single crystals to explore the scattering continuum around the Γ point at the Brillouin zone center,which was hypothesized to be resulting from the Kitaev QSL state but without concrete evidence.With polarization analyses,we find that,while the spin-wave excitations around the Γ point vanish above the transition temperature T_(N),the pure magnetic continuous excitations around the Γ point are robust against temperature.Furthermore,by calculating the dynamical spin-spin correlation function using the cluster perturbation theory,we derive magnetic dispersion spectra based on the K-Γ model,which involves with a ferromagnetic Kitaev interaction of −7.2 meV and an off-diagonal interaction of 5.6 meV.We find this model can reproduce not only the spin-wave excitation spectra around the Γ point,but also the non-spin-wave continuous magnetic excitations around the Γ point.These results provide evidence for the existence of fractional excitations around the Γ point originating from the Kitaev QSL state,and further support the validity of the K-Γ model as the effective minimal spin model to describe α-RuCl_(3).展开更多
As a new type of quantum state of matter hosting low energy relativistic quasiparticles,Weyl semimetals(WSMs)have attracted significant attention for scientific community and potential quantum device applications.In t...As a new type of quantum state of matter hosting low energy relativistic quasiparticles,Weyl semimetals(WSMs)have attracted significant attention for scientific community and potential quantum device applications.In this study,we present a comprehensive investigation of the structural,magnetic,and transport properties of noncentrosymmetric RAl Si(R=Sm,Ce),which have been predicted to be new magnetic WSM candidates.Both samples exhibit nonsaturated magnetoresistance,with about 900%and 80%for Sm Al Si and Ce Al Si,respectively,at temperature of 1.8 K and magnetic field of 9 T.The carrier densities of Sm Al Si and Ce Al Si exhibit remarkable change around magnetic transition temperatures,signifying that the electronic states are sensitive to the magnetic ordering of rare-earth elements.At low temperatures,Sm Al Si reveals prominent Shubnikov–de Haas oscillations associated with the nontrivial Berry phase.High-pressure experiments demonstrate that the magnetic order is robust and survival under high pressure.Our results would yield valuable insights into WSM physics and potentials in applications to next-generation spintronic devices in the RAl Si(R=Sm,Ce)family.展开更多
As one of the most promising Kitaev quantum-spin-liquid(QSL)candidates,α-RuCl_(3)has received a great deal of attention.However,its ground state exhibits a long-range zigzag magnetic order,which defies the QSL phase....As one of the most promising Kitaev quantum-spin-liquid(QSL)candidates,α-RuCl_(3)has received a great deal of attention.However,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.Here,we explore the evolution of magnetic excitations ofα-RuCl;under an in-plane magnetic field,by carrying out inelastic neutron scattering measurements on high-quality single crystals.Under zero field,there exist spin-wave excitations near the M point and a continuum near theΓpoint,which are believed to be associated with the zigzag magnetic order and fractional excitations of the Kitaev QSL state,respectively.By increasing the magnetic field,the spin-wave excitations gradually give way to the continuous excitations.On the verge of the critical fieldμ_(0)H_(c)=7.5 T,the former ones vanish and only the latter ones are left,indicating the emergence of a pure QSL state.By further increasing the field strength,the excitations near theΓpoint become more intense.By following the gap evolution of the excitations near theΓpoint,we are able to establish a phase diagram composed of three interesting phases,including a gapped zigzag order phase at low fields,possibly gapless QSL phase nearμ;H;,and gapped partially polarized phase at high fields.These results demonstrate that an in-plane magnetic field can driveα-RuCl;into a long-sought QSL state near the critical field.展开更多
Quantum spin liquids（QSLs） represent a novel state of matter in which quantum fluctuations prevent the conventional magnetic order from being established, and the spins remain disordered even at zero temperature. Th...Quantum spin liquids（QSLs） represent a novel state of matter in which quantum fluctuations prevent the conventional magnetic order from being established, and the spins remain disordered even at zero temperature. There have been many theoretical developments proposing various QSL states. On the other hand, experimental movement was relatively slow largely due to limitations on the candidate materials and difficulties in the measurements. In recent years, the experimental progress has been accelerated. In this topical review, we give a brief summary of experiments on the QSL candidates under magnetic fields. We arrange our discussions by two categories： i） Geometrically-frustrated systems, including triangularlattice compounds YbMgGaO4 and YbZnGaO4, κ-（BEDT-TTF）2 Cu2（CN）3, and EtMe3 Sb[Pd（dmit）2]2, and the kagom′e system ZnCu3（OH）6 Cl2; ii） the Kitaev material α-RuCl3. Among these, we will pay special attention to α-RuCl3, which has been intensively studied by ours and other groups recently. We will present evidence that both supports and rejects the QSL ground state for these materials, based on which we give several perspectives to stimulate further research activities.展开更多
基金the financial support from the National Key R&D Program of China(Grant No.2020YFA0309602)the National Natural Science Foundation of China(Grant No.11874042)+7 种基金the support from National Natural Science Foundation of China(Grant No.12004250)the support from the National Natural Science Foundation of China(Grant No.12004251)the National Natural Science Foundation of China(Grant Nos.11674326 and 11774351)the start-up funding from Shanghai Tech Universitythe Shanghai Sailing Program(Grant No.20YF1430700)the Shanghai Sailing Program(Grant No.21YF1429200)the support from the National Key R&D Program(Grant No.2021YFA1600201)the Joint Funds of the National Natural Science Foundation of China and the Chinese Academy of Sciences’Large-Scale Scientific Facility(Grant Nos.U1832141,U1932217 and U2032215)。
文摘Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation,but also is helpful for further understanding the heavy fermion superconductivity.Here we report a low-temperature and vector-magneticfield scanning tunneling microscopy and spectroscopy study on a superconducting compound(4Hb-TaS_(2))with alternate stacking of 1T-TaS_(2)and 1H-TaS_(2)layers.We observe the quasi-two-dimensional superconductivity in the 1H-TaS_(2)layer with anisotropic response to the in-plane and out-of-plane magnetic fields.In the 1T-TaS_(2)layer,we detect the Kondo resonance peak that results from the Kondo screening of the unpaired electrons in the Star-of-David clusters.We also find that the intensity of the Kondo resonance peak is sensitive to its relative position with the Fermi level,and it can be significantly enhanced when it is further shifted towards the Fermi level by evaporating Pb atoms onto the 1T-TaS_(2)surface.Our results not only are important for fully understanding the electronic properties of 4Hb-TaS_(2),but also pave the way for creating tunable Kondo lattice in the superconducting van der Waals materials.
基金supported in part by the National Natural Science Foundation of China (Nos. 61771234, 12004251)National Key Projects for Research and Development of China (No. 2017YFB0503302)+3 种基金the Natural Science Foundation of Shanghai (No. 20ZR1436100)the Science and Technology Commission of Shanghai Municipalitythe startup funding from ShanghaiTech UniversityBeijing National Laboratory for Condensed Matter Physics
基金supported by National Key Research and Development Program of China(Grant No.2021YFA1400400)the National Natural Science Foundation of China(Grant Nos.11822405,12074174,12074175,11774152,11904170,12004249,12004251,and 12004191)+3 种基金the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20180006,BK20190436 and BK20200738)the Shanghai Sailing Program(Grant Nos.20YF1430600 and21YF1429200)the Fundamental Research Funds for the Central Universities(Grant No.020414380183)the Office of International Cooperation and Exchanges of Nanjing University。
文摘It is known that α-RuCl_(3) has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid(QSL)phase and the possibility of approaching it by tuning the competing interactions.Here we present the first polarized inelastic neutron scattering study on α-RuCl_(3) single crystals to explore the scattering continuum around the Γ point at the Brillouin zone center,which was hypothesized to be resulting from the Kitaev QSL state but without concrete evidence.With polarization analyses,we find that,while the spin-wave excitations around the Γ point vanish above the transition temperature T_(N),the pure magnetic continuous excitations around the Γ point are robust against temperature.Furthermore,by calculating the dynamical spin-spin correlation function using the cluster perturbation theory,we derive magnetic dispersion spectra based on the K-Γ model,which involves with a ferromagnetic Kitaev interaction of −7.2 meV and an off-diagonal interaction of 5.6 meV.We find this model can reproduce not only the spin-wave excitation spectra around the Γ point,but also the non-spin-wave continuous magnetic excitations around the Γ point.These results provide evidence for the existence of fractional excitations around the Γ point originating from the Kitaev QSL state,and further support the validity of the K-Γ model as the effective minimal spin model to describe α-RuCl_(3).
基金supported by the National Key R&D Program of China(Grant Nos.2018YFA0704300 and 2017YFB0503302)the National Natural Science Foundation of China(Grant Nos.U1932217,11974246,12004252,61771234,and 12004251)+6 种基金the Natural Science Foundation of Shanghai(Grant Nos.19ZR1477300 and 20ZR1436100)the Science and Technology Commission of Shanghai Municipality(Grant Nos.19JC1413900 and YDZX20203100001438)the Shanghai Science and Technology Plan(Grant No.21DZ2260400),the Shanghai Sailing Program(Grant No.21YF1429200)the Interdisciplinary Program of Wuhan National High Magnetic Field Center(Grant No.WHMFC202124)the Beijing National Laboratory for Condensed Matter Physicsthe support from Analytical Instrumentation Center(Grant No.SPST-AIC10112914)Centre for High-resolution Electron Microscopy(ChEM)(Grant No.EM02161943),SPST,Shanghai Tech University。
文摘As a new type of quantum state of matter hosting low energy relativistic quasiparticles,Weyl semimetals(WSMs)have attracted significant attention for scientific community and potential quantum device applications.In this study,we present a comprehensive investigation of the structural,magnetic,and transport properties of noncentrosymmetric RAl Si(R=Sm,Ce),which have been predicted to be new magnetic WSM candidates.Both samples exhibit nonsaturated magnetoresistance,with about 900%and 80%for Sm Al Si and Ce Al Si,respectively,at temperature of 1.8 K and magnetic field of 9 T.The carrier densities of Sm Al Si and Ce Al Si exhibit remarkable change around magnetic transition temperatures,signifying that the electronic states are sensitive to the magnetic ordering of rare-earth elements.At low temperatures,Sm Al Si reveals prominent Shubnikov–de Haas oscillations associated with the nontrivial Berry phase.High-pressure experiments demonstrate that the magnetic order is robust and survival under high pressure.Our results would yield valuable insights into WSM physics and potentials in applications to next-generation spintronic devices in the RAl Si(R=Sm,Ce)family.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFA1400400)the National Natural Science Foundation of China(Grant Nos.11822405,12074174,12074175,92165205,11904170,12004249,12004251,and 12004191)+1 种基金the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20180006,BK20190436,and BK20200738)the Shanghai Sailing Program(Grant Nos.20YF1430600 and 21YF1429200)。
文摘As one of the most promising Kitaev quantum-spin-liquid(QSL)candidates,α-RuCl_(3)has received a great deal of attention.However,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.Here,we explore the evolution of magnetic excitations ofα-RuCl;under an in-plane magnetic field,by carrying out inelastic neutron scattering measurements on high-quality single crystals.Under zero field,there exist spin-wave excitations near the M point and a continuum near theΓpoint,which are believed to be associated with the zigzag magnetic order and fractional excitations of the Kitaev QSL state,respectively.By increasing the magnetic field,the spin-wave excitations gradually give way to the continuous excitations.On the verge of the critical fieldμ_(0)H_(c)=7.5 T,the former ones vanish and only the latter ones are left,indicating the emergence of a pure QSL state.By further increasing the field strength,the excitations near theΓpoint become more intense.By following the gap evolution of the excitations near theΓpoint,we are able to establish a phase diagram composed of three interesting phases,including a gapped zigzag order phase at low fields,possibly gapless QSL phase nearμ;H;,and gapped partially polarized phase at high fields.These results demonstrate that an in-plane magnetic field can driveα-RuCl;into a long-sought QSL state near the critical field.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674157 and 11822405)the Fundamental Research Funds for the Central Universities(Grant No.020414380105)
文摘Quantum spin liquids（QSLs） represent a novel state of matter in which quantum fluctuations prevent the conventional magnetic order from being established, and the spins remain disordered even at zero temperature. There have been many theoretical developments proposing various QSL states. On the other hand, experimental movement was relatively slow largely due to limitations on the candidate materials and difficulties in the measurements. In recent years, the experimental progress has been accelerated. In this topical review, we give a brief summary of experiments on the QSL candidates under magnetic fields. We arrange our discussions by two categories： i） Geometrically-frustrated systems, including triangularlattice compounds YbMgGaO4 and YbZnGaO4, κ-（BEDT-TTF）2 Cu2（CN）3, and EtMe3 Sb[Pd（dmit）2]2, and the kagom′e system ZnCu3（OH）6 Cl2; ii） the Kitaev material α-RuCl3. Among these, we will pay special attention to α-RuCl3, which has been intensively studied by ours and other groups recently. We will present evidence that both supports and rejects the QSL ground state for these materials, based on which we give several perspectives to stimulate further research activities.
