One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology.The existence of topological protected dissipationless surface state makes ...One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology.The existence of topological protected dissipationless surface state makes topological insulators great potential for applications and hotly studied.However,compared with the prosperity of strong topological insulators,theoretical predicted candidate materials and experimental confirmation of weak topological insulators(WTIs) are both extremely rare.By combining systematic first-principles calculation and angle-resolved photoemission spectroscopy measurements,we have studied the electronic structure of the dark surface of the WTI candidate Zintl Ba_(3)Cd_(2)Sb_(4)and another related material Ba_(3)Cd_(2)As_(4).The existence of two Dirac surface states on specific side surfaces predicted by theoretical calculations and the observed two band inversions in the Brillouin zone give strong evidence to prove that the Ba_(3)Cd_(2)Sb_(4)is a WTI.The spectroscopic characterization of this Zintl Ba_(3)Cd_(2)N_(4)(N = As and Sb) family materials will facilitate applications of their novel topological properties.展开更多
The search for new materials with Dirac points has been a fascinating subject of condensed matter physics.Here we first report the growth and band structure of HfGe_(0.92)Te single crystals featuring three different t...The search for new materials with Dirac points has been a fascinating subject of condensed matter physics.Here we first report the growth and band structure of HfGe_(0.92)Te single crystals featuring three different types of Dirac points.HfGe_(0.92)Te crystallizes in a nonsymmorphic tetragonal space group P4/nmm(No.129),having a square Ge-atom plane with vacancies of about 8%.Using angle-resolved photoemission spectroscopy(ARPES),the Dirac nodal line composed of conventional Dirac points vulnerable to spin-orbit coupling(SOC)is observed,accompanied by robust Dirac points protected by the nonsymmorphic symmetry against SOC and vacancies.In particular,spin-orbit Dirac points(SDPs)originating from the surface formed under significant SOC could exist based on ARPES and calculations.Quasi-two-dimensional(quasi-2D)characteristics are confirmed by angular-resolved magnetoresistance.HfGe_(0.92)Te bulk crystals can be easily exfoliated to flakes with a thickness of approximately 5 nm for the quasi-2D nature.Thus,HfGe_(0.92)Te provides a good platform to explore exotic topological phases or topological properties with three different types of Dirac points,which is a potential candidate to achieve novel 2D SDPs.展开更多
The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-re...The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-resolved photoemission spectroscopy,we have systematically investigated the(001)surface states of pristine and Ni-doped Co Si.The surface states form saddle-like band structures at/near the time-reversal invariant point near the Fermi level.The Fermi arcs undergo consecutive Lifshitz transitions at the saddle points X,leading to changes of the Fermi arc configuration.As the density of states has a van Hove singularity at the saddle points,exotic many-body physical phenomena may emerge accompanied by the topological transitions of surface Fermi arcs.展开更多
基金supported by the National Key R&D Program of China(Grant Nos.2022YFA1403800,2018YFA0305700,and 2019YFA0308602)the Chinese Academy of Sciences(Grant Nos.QYZDB-SSW-SLH043,XDB33000000,and XDB28000000)+2 种基金the National Natural Science Foundation of China (Grant Nos.U22A600018,U1832202,12074425,11874422,11925408,11921004,and 12188101)the Informatization Plan of Chinese Academy of Sciences (Grant No.CAS-WX2021SF-0102)the Synergetic Extreme Condition User Facility (SECUF)。
文摘One of the greatest triumph of condensed matter physics in the past ten years is the classification of materials by the principle of topology.The existence of topological protected dissipationless surface state makes topological insulators great potential for applications and hotly studied.However,compared with the prosperity of strong topological insulators,theoretical predicted candidate materials and experimental confirmation of weak topological insulators(WTIs) are both extremely rare.By combining systematic first-principles calculation and angle-resolved photoemission spectroscopy measurements,we have studied the electronic structure of the dark surface of the WTI candidate Zintl Ba_(3)Cd_(2)Sb_(4)and another related material Ba_(3)Cd_(2)As_(4).The existence of two Dirac surface states on specific side surfaces predicted by theoretical calculations and the observed two band inversions in the Brillouin zone give strong evidence to prove that the Ba_(3)Cd_(2)Sb_(4)is a WTI.The spectroscopic characterization of this Zintl Ba_(3)Cd_(2)N_(4)(N = As and Sb) family materials will facilitate applications of their novel topological properties.
基金partially supported by the National Natural Science Foundation of China(Grant Nos.51832010,51902055,11925408,12005251,and 11921004)National Key Research and Development Program of China(Grant Nos.2018YFE0202602,2018YFA0305700,and 2017YFA0302902)。
文摘The search for new materials with Dirac points has been a fascinating subject of condensed matter physics.Here we first report the growth and band structure of HfGe_(0.92)Te single crystals featuring three different types of Dirac points.HfGe_(0.92)Te crystallizes in a nonsymmorphic tetragonal space group P4/nmm(No.129),having a square Ge-atom plane with vacancies of about 8%.Using angle-resolved photoemission spectroscopy(ARPES),the Dirac nodal line composed of conventional Dirac points vulnerable to spin-orbit coupling(SOC)is observed,accompanied by robust Dirac points protected by the nonsymmorphic symmetry against SOC and vacancies.In particular,spin-orbit Dirac points(SDPs)originating from the surface formed under significant SOC could exist based on ARPES and calculations.Quasi-two-dimensional(quasi-2D)characteristics are confirmed by angular-resolved magnetoresistance.HfGe_(0.92)Te bulk crystals can be easily exfoliated to flakes with a thickness of approximately 5 nm for the quasi-2D nature.Thus,HfGe_(0.92)Te provides a good platform to explore exotic topological phases or topological properties with three different types of Dirac points,which is a potential candidate to achieve novel 2D SDPs.
基金supported by the National Natural Science Foundation of China(U1832202,11888101,11920101005,12141402,and 12274459)the Chinese Academy of Sciences(QYZDB-SSW-SLH043,XDB33020100,and XDB28000000)+4 种基金the Beijing Municipal Science and Technology Commission(Z171100002017018,and Z200005)the National Key R&D Program of China(2018YFE0202600,2022YFA1403100,and 2022YFA1403800)the Fundamental Research Funds for the Central Universities and Research Funds of Renmin University of China(RUC)(18XNLG14,19XNLG13,19XNLG17,and 20XNH062)the Synergic Extreme Condition User Facility,Beijing,ChinaBeijing National Laboratory for Condensed Matter Physics。
基金supported by the Ministry of Science and Technology of China(Grant Nos.2016YFA0401000,2016YFA0300600,2018YFE0202600,and 2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.U1832202,11774423,118224121,and 1888101)+4 种基金the Chinese Academy of Sciences(Grant Nos.QYZDB-SSW-SLH043,XDB33020100,and XDB28000000)the Beijing Natural Science Foundation(Grant No.Z200005)the Fundamental Research Funds for the Central Universities and Research Funds of Renmin University of China(Grant Nos.18XNLG14,and 19XNLG17)the Beijing Municipal Science and Technology Commission(Grant No.Z171100002017018)support by the CAS Pioneer“Hundred Talents Program”(type C)。
文摘The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-resolved photoemission spectroscopy,we have systematically investigated the(001)surface states of pristine and Ni-doped Co Si.The surface states form saddle-like band structures at/near the time-reversal invariant point near the Fermi level.The Fermi arcs undergo consecutive Lifshitz transitions at the saddle points X,leading to changes of the Fermi arc configuration.As the density of states has a van Hove singularity at the saddle points,exotic many-body physical phenomena may emerge accompanied by the topological transitions of surface Fermi arcs.
