We performed angle-resolved photoemission spectroscopy studies on a series of FeTe_(1-x)Se_x monolayer films grown on Sr TiO_3.The superconductivity of the films is robust and rather insensitive to the variations of t...We performed angle-resolved photoemission spectroscopy studies on a series of FeTe_(1-x)Se_x monolayer films grown on Sr TiO_3.The superconductivity of the films is robust and rather insensitive to the variations of the band position and effective mass caused by the substitution of Se by Te.However,the band gap between the electron-and hole-like bands at the Brillouin zone center decreases towards band inversion and parity exchange,which drive the system to a nontrivial topological state predicted by theoretical calculations.Our results provide a clear experimental indication that the FeTe_(1-x)Se_x monolayer materials are high-temperature connate topological superconductors in which band topology and superconductivity are integrated intrinsically.展开更多
In three-dimensional noncentrosymmetric materials two-fold screw rotation symmetry forces electron＇s energy bands to have Weyl points at which two bands touch. This is illustrated for space groups No. 19 （P212121 ）...In three-dimensional noncentrosymmetric materials two-fold screw rotation symmetry forces electron＇s energy bands to have Weyl points at which two bands touch. This is illustrated for space groups No. 19 （P212121 ） and No. 198 （P213）, which have three orthogonal screw rotation axes. In the case of space groups No. 61 （Pbca） and No. 205 （Pa-3） that have extra inversion symmetry, Weyl points are promoted to four-fold degenerate line nodes in glide-invariant planes. The three-fold rotation symmetry present in the space groups No. 198 and No. 205 allows Weyl and Dirac points, respectively, to appear along its rotation axes in the Brillouin zone and generates four-fold and six-fold degeneracy at the F point and R point, respectively.展开更多
Higher-order topological phases(HOTPs) are systems with topologically protected in-gap boundary states localized at their ed à nT-dimensional boundaries, with d the system dimension and n the order of the topolog...Higher-order topological phases(HOTPs) are systems with topologically protected in-gap boundary states localized at their ed à nT-dimensional boundaries, with d the system dimension and n the order of the topology. This work proposes a dynamics-based characterization of one large class of Z-type HOTPs without specifically relying on any crystalline symmetry considerations. The key element of our innovative approach is to connect quantum quench dynamics with nested configurations of the socalled band inversion surfaces(BISs) of momentum-space Hamiltonians as a sum of operators from the Clifford algebra(a condition that can be partially relaxed), thereby making it possible to dynamically detect each and every order of topology on an equal footing. Given that experiments on synthetic topological matter can directly measure the winding of certain pseudospin texture to determine topological features of BISs, the topological invariants defined through nested BISs are all within reach of ongoing experiments. Further, the necessity of having nested BISs in defining higher-order topology offers a unique perspective to investigate and engineer higher-order topological phase transitions.展开更多
基金supported by grants from the Ministry of Science and Technology of China(2015CB921000,2016YFA0401000,2015CB921301,2016YFA0300300)the National Natural Science Foundation of China(11574371,11274362,1190020,11334012,11274381,11674371)
文摘We performed angle-resolved photoemission spectroscopy studies on a series of FeTe_(1-x)Se_x monolayer films grown on Sr TiO_3.The superconductivity of the films is robust and rather insensitive to the variations of the band position and effective mass caused by the substitution of Se by Te.However,the band gap between the electron-and hole-like bands at the Brillouin zone center decreases towards band inversion and parity exchange,which drive the system to a nontrivial topological state predicted by theoretical calculations.Our results provide a clear experimental indication that the FeTe_(1-x)Se_x monolayer materials are high-temperature connate topological superconductors in which band topology and superconductivity are integrated intrinsically.
基金supported by JSPS Kakenhi(No.15K05141)from Japan Society for the Promotion of Science
文摘In three-dimensional noncentrosymmetric materials two-fold screw rotation symmetry forces electron＇s energy bands to have Weyl points at which two bands touch. This is illustrated for space groups No. 19 （P212121 ） and No. 198 （P213）, which have three orthogonal screw rotation axes. In the case of space groups No. 61 （Pbca） and No. 205 （Pa-3） that have extra inversion symmetry, Weyl points are promoted to four-fold degenerate line nodes in glide-invariant planes. The three-fold rotation symmetry present in the space groups No. 198 and No. 205 allows Weyl and Dirac points, respectively, to appear along its rotation axes in the Brillouin zone and generates four-fold and six-fold degeneracy at the F point and R point, respectively.
基金supported by the National Basic Research Program of China(2019YFA0308403 and 2022YFA1403700)the National Natural Science Foundation of China(12147126)Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions。
基金the Singapore Ministry of Education Academic Research Fund Tier-3 Grant No.MOE2017T3-1-001(WBS.No.R-144-000-425-592)the Singapore National Research Foundation Grant No.NRF-NRFI2017-04(WBS No.R-144-000-378-281)。
文摘Higher-order topological phases(HOTPs) are systems with topologically protected in-gap boundary states localized at their ed à nT-dimensional boundaries, with d the system dimension and n the order of the topology. This work proposes a dynamics-based characterization of one large class of Z-type HOTPs without specifically relying on any crystalline symmetry considerations. The key element of our innovative approach is to connect quantum quench dynamics with nested configurations of the socalled band inversion surfaces(BISs) of momentum-space Hamiltonians as a sum of operators from the Clifford algebra(a condition that can be partially relaxed), thereby making it possible to dynamically detect each and every order of topology on an equal footing. Given that experiments on synthetic topological matter can directly measure the winding of certain pseudospin texture to determine topological features of BISs, the topological invariants defined through nested BISs are all within reach of ongoing experiments. Further, the necessity of having nested BISs in defining higher-order topology offers a unique perspective to investigate and engineer higher-order topological phase transitions.
基金supported by the EIPHI Graduate School(Grant No.ANR-17-EURE-0002)the U.S.National Science Foundation(Grant Nos.DMR-1823800,CMMI-2131760 and CMMI-1930873).
