Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolutio...Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism,with the combination of angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory calculations,we investigate how band dispersions change with the increase of lattice distortions.In particular,we focus on the electronic states around M point,where the van Hove singularities are expected to play crucial roles in the CDW transition.Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M point,which is associated with the 3D lattice modulations.Our studies reveal that this“splitting”can be connected to the two van Hove singularities at k_(z)=0 and k_(z)=π/c in the normal states.When the electronic system enters into the CDW state,both van Hove singularities move down.Such novel properties are important for understanding of the CDW transition.展开更多
Transition-metal oxyhalides MOX(M=Fe,Cr,V;O=oxygen,X=F,Cl,Br,I),an emerging type of two-dimensional(2D)van der Waals materials,have been both theoretically and experimentally demonstrated to possess unique electronic ...Transition-metal oxyhalides MOX(M=Fe,Cr,V;O=oxygen,X=F,Cl,Br,I),an emerging type of two-dimensional(2D)van der Waals materials,have been both theoretically and experimentally demonstrated to possess unique electronic and magnetic properties.However,the intrinsic in-plane anisotropic properties of 2D VOCl still lacks in-depth re-search,especially optical anisotropy.Herein,a systematic Raman spectroscopic study is performed on VOCl single-crystal with different incident laser polarization at various temperatures.The polarized-dependent Raman scattering spectra reveal that the Ag mode of VOCl show a 2-lobed shape in parallel polarization configuration while a 4-lobed shape in vertical configuration.In addition,the temperature-dependent and thickness-dependent Raman scattering spectra confirm a rela-tively weak van der Waals interaction between each layers among VOCl single crystal.These findings might provide better understanding on the in-plane anisotropic phenomenon in VOCl layers,thus will accelate further application of 2D single crystals for nanoscale angle-dependent optoelectronics.展开更多
Tuning the bandgap in layered transition metal dichalcogenides(TMDCs) is crucial for their versatile applications in many fields. The ternary formation is a viable method to tune the bandgap as well as other intrinsic...Tuning the bandgap in layered transition metal dichalcogenides(TMDCs) is crucial for their versatile applications in many fields. The ternary formation is a viable method to tune the bandgap as well as other intrinsic properties of TMDCs, because the multi-elemental characteristics provide additional tunability at the atomic level and advantageously alter the physical properties of TMDCs. Herein, ternary Ti_(x)Zr_(1-x)Se_(2) single crystals were synthesized using the chemical-vapor-transport method. The changes in electronic structures of ZrSe_(2) induced by Ti substitution were revealed using angle-resolved photoemission spectroscopy. Our data show that at a low level of Ti substitution, the bandgap of Ti_(x)Zr_(1-x)Se_(2) decreases monotonically, and the electronic system undergoes a transition from a semiconducting to a metallic state without a significant variation of dispersions of valence bands. Meanwhile, the size of spin-orbit splitting dominated by Se 4p orbitals decreases with the increase of Ti doping. Our work shows a convenient way to alter the bandgap and spin-orbit coupling in TMDCs at the low level of substitution of transition metals.展开更多
基金supported by the National Key R&D Program of China (Grant No.2017YFA0402901)the National Natural Science Foundation of China (Grant No.U2032153)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDB25000000)the Users with Excellence Program of Hefei Science Center of the Chinese Academy of Sciences (Grant No.2021HSC-UE004)。
文摘Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism,with the combination of angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory calculations,we investigate how band dispersions change with the increase of lattice distortions.In particular,we focus on the electronic states around M point,where the van Hove singularities are expected to play crucial roles in the CDW transition.Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M point,which is associated with the 3D lattice modulations.Our studies reveal that this“splitting”can be connected to the two van Hove singularities at k_(z)=0 and k_(z)=π/c in the normal states.When the electronic system enters into the CDW state,both van Hove singularities move down.Such novel properties are important for understanding of the CDW transition.
基金Project financially supported by National Natural Science Foundation of China (Grant No. U1932201)the International Partnership Program (Grant No. 211134KYSB20190063)+3 种基金the CAS (Chinese Academy of Sciences) Collaborative Innovation Program of Hefei Science Center (Grant No. 2020HSCCIP002)the University Synergy Innovation Program of Anhui Province, China (Grant No. GXXT-2020-002)the Youth Innovation Promotion Association of CAS (Grant No. 2022457)the USTC Research Funds of the Double First-Class Initiative (YD2310002004)
文摘Transition-metal oxyhalides MOX(M=Fe,Cr,V;O=oxygen,X=F,Cl,Br,I),an emerging type of two-dimensional(2D)van der Waals materials,have been both theoretically and experimentally demonstrated to possess unique electronic and magnetic properties.However,the intrinsic in-plane anisotropic properties of 2D VOCl still lacks in-depth re-search,especially optical anisotropy.Herein,a systematic Raman spectroscopic study is performed on VOCl single-crystal with different incident laser polarization at various temperatures.The polarized-dependent Raman scattering spectra reveal that the Ag mode of VOCl show a 2-lobed shape in parallel polarization configuration while a 4-lobed shape in vertical configuration.In addition,the temperature-dependent and thickness-dependent Raman scattering spectra confirm a rela-tively weak van der Waals interaction between each layers among VOCl single crystal.These findings might provide better understanding on the in-plane anisotropic phenomenon in VOCl layers,thus will accelate further application of 2D single crystals for nanoscale angle-dependent optoelectronics.
基金supported by the National Key R&D Program of China (Grant No. 2017YFA0402901)the National Natural Science Foundation of China (Grant No. U2032153)+2 种基金the International Partnership Program (Grant No. 211134KYSB20190063)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB25000000)the USTC Research Funds of the Double First-Class Initiative (Grant No. YD2310002004)。
文摘Tuning the bandgap in layered transition metal dichalcogenides(TMDCs) is crucial for their versatile applications in many fields. The ternary formation is a viable method to tune the bandgap as well as other intrinsic properties of TMDCs, because the multi-elemental characteristics provide additional tunability at the atomic level and advantageously alter the physical properties of TMDCs. Herein, ternary Ti_(x)Zr_(1-x)Se_(2) single crystals were synthesized using the chemical-vapor-transport method. The changes in electronic structures of ZrSe_(2) induced by Ti substitution were revealed using angle-resolved photoemission spectroscopy. Our data show that at a low level of Ti substitution, the bandgap of Ti_(x)Zr_(1-x)Se_(2) decreases monotonically, and the electronic system undergoes a transition from a semiconducting to a metallic state without a significant variation of dispersions of valence bands. Meanwhile, the size of spin-orbit splitting dominated by Se 4p orbitals decreases with the increase of Ti doping. Our work shows a convenient way to alter the bandgap and spin-orbit coupling in TMDCs at the low level of substitution of transition metals.