Traditionally topological phase transition describes an evolution from topological trivial to topological nontrivial state.Originated from the non-symmorphic crystalline symmetry,we propose in this work an unconventio...Traditionally topological phase transition describes an evolution from topological trivial to topological nontrivial state.Originated from the non-symmorphic crystalline symmetry,we propose in this work an unconventional topological phase transition scheme between two topological nontrivial insulating states mediated by a Dirac gapless state,differing from the traditional topological phase transition.The KHgX(X=As,Sb,Bi)family is the first experimentally realized topological non-symmorphic crystalline insulator(TNCI),where the topological surface states are characterized by the Mobius-twisted connectivity.Based on first-principles calculations,we present a topological insulator–metal transition from TNCI into a Dirac semimetal(DSM)via applying an external pressure on KHgX.We find an unusual mirror Chern number C_(m)=−3 for the DSM phase of KHgX in the non-symmorphic crystal structure,which is topologically distinct from the traditional DSM such as Na_(3)Bi and Cd_(3)As_(2).Furthermore,we predict a new TNCI phase in KHgX via symmetry breaking.The topological surface states in this new TNCI phase display zigzag connectivity,different from the unstressed one.Our results offer a comprehensive study for understanding how the topological surface states evolve from a quantum phase transition in non-symmorphic system.展开更多
Protected surface states arising fromnon-trivial bandstructure topology in semimetals can potentially enable advanced device functionalities in compute,memory,interconnect,sensing,and communication.This necessitates a...Protected surface states arising fromnon-trivial bandstructure topology in semimetals can potentially enable advanced device functionalities in compute,memory,interconnect,sensing,and communication.This necessitates a fundamental understanding of surface-state transport in nanoscale topological semimetals.Here,we investigate quantum transport in a prototypical topological semimetal NbAs to evaluate the potential of this class of materials for beyond-Cu interconnects in highly-scaled integrated circuits.Using density functional theory(DFT)coupled with non-equilibrium Green’s function(NEGF)calculations,we show that the resistance-areaRAproduct in NbAs films decreases with decreasing thickness at the nanometer scale,in contrast to a nearly constant RA product in ideal Cu films.This anomalous scaling originates from the disproportionately large number of surface conduction states which dominate the ballistic conductance by up to 70%in NbAs thin films.We also show that this favorable RA scaling persists even in the presence of surface defects,in contrast to RA sharply increasing with reducing thickness for films of conventional metals,such as Cu,in the presence of surface defects.These results underscore the potential of topological semimetals as future back-end-of-line(BEOL)interconnect metals.展开更多
基金This work was supported by the Ministry of Science and Technology,Taiwan,Grant Nos.MOST 107-2627-E-006-001 and MOST 106-2112-M-007-012-MY3T.-R.C.was supported from Young Scholar Fellowship Program by Ministry of Science and Technology(MOST)in Taiwan,under MOST Grant for the Columbus Program MOST108-2636-M-006-002。
文摘Traditionally topological phase transition describes an evolution from topological trivial to topological nontrivial state.Originated from the non-symmorphic crystalline symmetry,we propose in this work an unconventional topological phase transition scheme between two topological nontrivial insulating states mediated by a Dirac gapless state,differing from the traditional topological phase transition.The KHgX(X=As,Sb,Bi)family is the first experimentally realized topological non-symmorphic crystalline insulator(TNCI),where the topological surface states are characterized by the Mobius-twisted connectivity.Based on first-principles calculations,we present a topological insulator–metal transition from TNCI into a Dirac semimetal(DSM)via applying an external pressure on KHgX.We find an unusual mirror Chern number C_(m)=−3 for the DSM phase of KHgX in the non-symmorphic crystal structure,which is topologically distinct from the traditional DSM such as Na_(3)Bi and Cd_(3)As_(2).Furthermore,we predict a new TNCI phase in KHgX via symmetry breaking.The topological surface states in this new TNCI phase display zigzag connectivity,different from the unstressed one.Our results offer a comprehensive study for understanding how the topological surface states evolve from a quantum phase transition in non-symmorphic system.
基金the National University of Singapore was supported by MOE-2017-T2-2-114,MOE-2019-T2-2-215,and FRC-A-8000194-01-00supported by 2030 Cross-Generation Young Scholars Program from the Science and Technology Council(MOST111-2628-M-006-003-MY3)Cheng Kung University,and the Center for Theoretical Sciences.
文摘Protected surface states arising fromnon-trivial bandstructure topology in semimetals can potentially enable advanced device functionalities in compute,memory,interconnect,sensing,and communication.This necessitates a fundamental understanding of surface-state transport in nanoscale topological semimetals.Here,we investigate quantum transport in a prototypical topological semimetal NbAs to evaluate the potential of this class of materials for beyond-Cu interconnects in highly-scaled integrated circuits.Using density functional theory(DFT)coupled with non-equilibrium Green’s function(NEGF)calculations,we show that the resistance-areaRAproduct in NbAs films decreases with decreasing thickness at the nanometer scale,in contrast to a nearly constant RA product in ideal Cu films.This anomalous scaling originates from the disproportionately large number of surface conduction states which dominate the ballistic conductance by up to 70%in NbAs thin films.We also show that this favorable RA scaling persists even in the presence of surface defects,in contrast to RA sharply increasing with reducing thickness for films of conventional metals,such as Cu,in the presence of surface defects.These results underscore the potential of topological semimetals as future back-end-of-line(BEOL)interconnect metals.
