TiSe_(2)is a narrow-gap insulator with a rich array of unique properties.In addition to being a superconductor under certain modifications,it is commonly thought to be a rare realisation of an excitonic insulator.Belo...TiSe_(2)is a narrow-gap insulator with a rich array of unique properties.In addition to being a superconductor under certain modifications,it is commonly thought to be a rare realisation of an excitonic insulator.Below 200 K,TiSe_(2)undergoes a transition from a high-symmetry(P3^(-)m1)phase to a low-symmetry(P3^(-)c1)charge density wave(CDW).Here we establish that it is indeed an insulator in both P3^(-)m1 and P3^(-)c1 phases.However,the insulating state is driven not by excitonic effects but by symmetry-breaking.In theCDWphase it is static.At high temperature,thermally driven instantaneous deviations from P3^(-)m1 break the symmetry on the characteristic time scale of a phonon.Even though the time-averaged lattice structure assumes P3^(-)m1 symmetry,the time-averaged energy band structure is closer to the CDW phase–a rare instance of a metal-insulator transition induced by dynamical symmetry breaking.We establish these conclusions from quasiparticle self-consistent GW(QSGW)and many-body calculations(QSG b W),incombination withmolecular dynamics simulations to capture the effects of thermal disorder.The many-body theory includes explicitly ladder diagrams in the polarizability,which incorporates excitonic effects in an ab initio manner.We find that the excitonic modification to the potential is weak,ruling out the possibility that TiSe_(2)is an excitonic insulator.展开更多
基金the National Renewable Energy Laboratory for the U.S.Department of Energy(DOE)under Contract No.DE-AC36-08GO28308 Funding was provided by Office of Science,Basic Energy Sciences,Division of MaterialsWe acknowledge the use of the National Energy Research Scientific Computing Center,under Contract No.DE-AC02-05CH11231 using NERSC award BES-ERCAP0021783we also acknowledge that a portion of the research was performed using computational resources sponsored by the Department of Energy’s Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory,and computational resources provided by the Oakridge leadership Computing Facility.The views expressed in the article do not necessarily represent the views of the DOE or the U.S.Government.The U.S.Government retains and the publisher,by accepting the article for publication,acknowledges that the U.S.Government retains a nonexclusive,paid-up,irrevocable,worldwide license to publish or reproduce the published form of this work,or allow others to do so,for U.S.Government purposes.
文摘TiSe_(2)is a narrow-gap insulator with a rich array of unique properties.In addition to being a superconductor under certain modifications,it is commonly thought to be a rare realisation of an excitonic insulator.Below 200 K,TiSe_(2)undergoes a transition from a high-symmetry(P3^(-)m1)phase to a low-symmetry(P3^(-)c1)charge density wave(CDW).Here we establish that it is indeed an insulator in both P3^(-)m1 and P3^(-)c1 phases.However,the insulating state is driven not by excitonic effects but by symmetry-breaking.In theCDWphase it is static.At high temperature,thermally driven instantaneous deviations from P3^(-)m1 break the symmetry on the characteristic time scale of a phonon.Even though the time-averaged lattice structure assumes P3^(-)m1 symmetry,the time-averaged energy band structure is closer to the CDW phase–a rare instance of a metal-insulator transition induced by dynamical symmetry breaking.We establish these conclusions from quasiparticle self-consistent GW(QSGW)and many-body calculations(QSG b W),incombination withmolecular dynamics simulations to capture the effects of thermal disorder.The many-body theory includes explicitly ladder diagrams in the polarizability,which incorporates excitonic effects in an ab initio manner.We find that the excitonic modification to the potential is weak,ruling out the possibility that TiSe_(2)is an excitonic insulator.
