Common microscopic origin of the phase transitions in Ta_(2)NiS_(5) and the excitonic insulator candidate Ta_(2)NiSe_(5)  

作　　者：Lukas Windgätter Malte Rösner Giacomo Mazza Hannes Hübener Antoine Georges Andrew J.Millis Simone Latini Angel Rubio 

机构地区：[1]Max Planck Institute for the Structure and Dynamics of Matter,Luruper Chaussee 149,22761 Hamburg,Gemany [2]Radboud University,Institute for Molecules and Materials,Heijendaalseweg 135,6525 AJ Nijmegen,Netherlands [3]Department of Quantum Matter Physics,University of Geneva,Quai Ernest-Ansermet 24,1211 Geneva,Switzerland [4]College de France,11 place Marcelin Berthelot,75005 Paris,France [5]Center for Computational Quantum Physics,Flatiron Institute,New York,NY 10010,USA.CPHT,CNRS,Ecole Polytechnique,IP Paris,91128 Palaiseau,France [6]Department of Physics,Columbia University,New York,NY 10027,USA.Nano-Bio Spectroscopy Group [7]Departamento de Fisica de Materiales,Universidad del Pais Vasco,20018 San Sebastian,Spain

出　　处：《npj Computational Materials》2021年第1期1919-1932,共14页计算材料学（英文）

基　　金：We are grateful to E.Baldini,I.Mazin and Yann Gallais for enlightening discussions throughout the course of this work.We would like to thank M.Ye,G.Blumberg,K.Kim,BJ.Kim,MJ.Kim and S.Kaiser for sharing the experimental data of their Raman measurements and valuable discussions.This work is supported by the European Research Council(ERC-2015-AdG-694097);Grupos Consolidados(IT1249-19);the Flatiron Institute,a division of the Simons Foundation.We acknowledge funding by the Deutsche Forschungsgemeinschaft(DFG)under Germany's Excellence Strategy-Cluster of Excellence Advanced Imaging of Matter(AIM)EXC 2056-390715994;by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-SFB-925-project 170620586;Support by the MaxPlanck Institute-New York City Center for Non-Equilibrium Quantum Phenomena is acknowledged;S.L.acknowledges support from the Alexander von Humboldt foundation;G.M.acknowledges support of the Swiss National Science Foundation FNS/SNF through an Ambizione grant.

摘　　要：The structural phase transition in Ta-NiSes has been envisioned as driven by the formation of an excitonic insulating phase.However,the role of structural and electronic instabilities on crystal symmetry breaking has yet to be disentangled.Meanwhile,the phase transition in its complementary material Ta_(2)NiS_(5)does not show any experimental hints of an excitonic insulating phase.We present a microscopic investigation of the electronic and phononic effects involved in the structural phase transition in Ta_(2)NiSe_(5)and Ta-Niss using extensive first-principles calculations.In both materials the crystal symmetries are broken by phonon instabilities,which in tum lead to changes in the electronic bandstructure also observed in the experiment.A total energy landscape analysis shows no tendency towards a purely electronic instability and we find that a sizeable lattice distortion is needed to open a bandgap.We conclude that an excitonic instability is not needed to explain the phase transition in both Ta_(2)NiSe_(5)and Ta_(2)NiS_(5).

关 键 词：phase STRUCTURAL TRANSITIONS 

分 类 号：TB33[一般工业技术—材料科学与工程]