Delocalization of dark and bright excitons in flat-band materials and the optical properties of V_(2)O_(5)  

作　　者：Vitaly Gorelov Lucia Reining Martin Feneberg Rüdiger Goldhahn AndréSchleife Walter R.L.Lambrecht Matteo Gatti 

机构地区：[1]LSI,CNRS,CEA/DRF/IRAMIS,École Polytechnique,Institut Polytechnique de Paris,F-91120,Palaiseau,France [2]European Theoretical Spectroscopy Facility https://www.etsf.eu/ [3]Institute of Physics,Otto von Guericke University Magdeburg,Universitätsplatz 2,39106,Magdeburg,Germany [4]Department of Materials Science and Engineering,University of Illinois at Urbana-Champaign,Urbana,IL,61801,USA [5]Materials Research Laboratory,University of Illinois at Urbana-Champaign,Urbana,IL,61801,USA [6]National Center for Supercomputing Applications,University of Illinois at Urbana-Champaign,Urbana,IL,61801,USA [7]Department of Physics,Case Western Reserve University,Cleveland,OH,44106-7079,USA [8]Synchrotron SOLEIL,L’Orme des Merisiers,Saint-Aubin BP 48,F-91192,Gif-sur-Yvette,France

出　　处：《npj Computational Materials》2022年第1期882-890,共9页计算材料学（英文）

基　　金：This work benefited from the support of EDF in the framework of the research and teaching Chair “Sustainable energies” at Ecole Polytechnique.Computational time was granted by GENCI (Project No.544);W.R.L.L.was supported by the U.S.Department of Energy-Basic Energy Sciences (DOE-BES) grant no.DE-SC0008933;This material is in part based upon work supported by the National Science Foundation under grant no.DMR-1555153;This research is part of the Blue Waters sustained-petascale computing project,which is supported by the National Science Foundation (awards OCI-0725070 and ACI-1238993) and the state of Illinois。

摘　　要：The simplest picture of excitons in materials with atomic-like localization of electrons is that of Frenkel excitons,where electrons and holes stay close together,which is associated with a large binding energy.Here,using the example of the layered oxide V_(2)O_(5),we show how localized charge-transfer excitations combine to form excitons that also have a huge binding energy but,at the same time,a large electron-hole distance,and we explain this seemingly contradictory finding.The anisotropy of the exciton delocalization is determined by the local anisotropy of the structure,whereas the exciton extends orthogonally to the chains formed by the crystal structure.Moreover,we show that the bright exciton goes together with a dark exciton of even larger binding energy and more pronounced anisotropy.These findings are obtained by combining first principles many-body perturbation theory calculations,ellipsometry experiments,and tight binding modelling,leading to very good agreement and a consistent picture.Our explanation is general and can be extended to other materials.

关 键 词：structure ANISOTROPY finding 

分 类 号：O47[理学—半导体物理]