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
An application-expected ideal two-dimensional Rashba electron gas,i.e.,nearly all the conduction electrons occupy the Rashba bands,is crucial for semiconductor spintronic applications.We demonstrate that such an ideal...An application-expected ideal two-dimensional Rashba electron gas,i.e.,nearly all the conduction electrons occupy the Rashba bands,is crucial for semiconductor spintronic applications.We demonstrate that such an ideal two-dimensional Rashba electron gas with a large Rashba splitting can be realized in a topological insulator Bi_(2)Se_(3) ultrathin film grown on a transition metal dichalcogenides MoTe_(2) substrate through first-principle calculations.Our results show the Rashba bands exclusively over a very large energy interval of about 0.6 eV around the Fermi level within the MoTe2 semiconducting gap.Such a wide-range ideal twodimensional Rashba electron gas with a large spin splitting,which is desirable for real devices utilizing the Rashba effect,has never been found before.Due to the strong spin-orbit coupling,the strength of the Rashba splitting is comparable with that of the heavy-metal surfaces such as Au and Bi surfaces,giving rise to a spin precession length as small as~10 nm.The maximum in-plane spin polarization of the inner(outer)Rashba band near theΓpoint is about 70%(60%).The room-temperature coherence length is at least several times longer than the spin precession length,providing good coherency through the spin processing devices.The wide energy window for ideal Rashba bands,small spin precession length,as well as long spin coherence length in this twodimensional topological insulator/transition metal dichalcogenides heterostructure pave the way for realizing an ultrathin nanoscale spintronic device such as the Datta-Das spin transistor at room-temperature.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supported by the Ministry of Science and Technology,Taiwan.
文摘An application-expected ideal two-dimensional Rashba electron gas,i.e.,nearly all the conduction electrons occupy the Rashba bands,is crucial for semiconductor spintronic applications.We demonstrate that such an ideal two-dimensional Rashba electron gas with a large Rashba splitting can be realized in a topological insulator Bi_(2)Se_(3) ultrathin film grown on a transition metal dichalcogenides MoTe_(2) substrate through first-principle calculations.Our results show the Rashba bands exclusively over a very large energy interval of about 0.6 eV around the Fermi level within the MoTe2 semiconducting gap.Such a wide-range ideal twodimensional Rashba electron gas with a large spin splitting,which is desirable for real devices utilizing the Rashba effect,has never been found before.Due to the strong spin-orbit coupling,the strength of the Rashba splitting is comparable with that of the heavy-metal surfaces such as Au and Bi surfaces,giving rise to a spin precession length as small as~10 nm.The maximum in-plane spin polarization of the inner(outer)Rashba band near theΓpoint is about 70%(60%).The room-temperature coherence length is at least several times longer than the spin precession length,providing good coherency through the spin processing devices.The wide energy window for ideal Rashba bands,small spin precession length,as well as long spin coherence length in this twodimensional topological insulator/transition metal dichalcogenides heterostructure pave the way for realizing an ultrathin nanoscale spintronic device such as the Datta-Das spin transistor at room-temperature.
