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DOI	10.1073/pnas.2010110118
	Evidence of ideal excitonic insulator in bulk MoS2 under pressure
	Samaneh Ataei S.; Varsano D.; Molinari E.; Rontani M.
发表日期	2021
ISSN	00278424
卷号	118 期号:13
英文摘要	Spontaneous condensation of excitons is a long-sought phenomenon analogous to the condensation of Cooper pairs in a superconductor. It is expected to occur in a semiconductor at thermodynamic equilibrium if the binding energy of the excitons—electron (e) and hole (h) pairs interacting by Coulomb force—overcomes the band gap, giving rise to a new phase: the “excitonic insulator” (EI). Transition metal dichalcogenides are excellent candidates for the EI realization because of reduced Coulomb screening, and indeed a structural phase transition was observed in few-layer systems. However, previous work could not disentangle to which extent the origin of the transition was in the formation of bound excitons or in the softening of a phonon. Here we focus on bulk MoS2 and demonstrate theoretically that at high pressure it is prone to the condensation of genuine excitons of finite momentum, whereas the phonon dispersion remains regular. Starting from first-principles many-body perturbation theory, we also predict that the self-consistent electronic charge density of the EI sustains an out-of-plane permanent electric dipole moment with an antiferroelectric texture in the layer plane: At the onset of the EI phase, those optical phonons that share the exciton momentum provide a unique Raman fingerprint for the EI formation. Finally, we identify such fingerprint in a Raman feature that was previously observed experimentally, thus providing direct spectroscopic confirmation of an ideal excitonic insulator phase in bulk MoS2 above 30 GPa. © 2021 National Academy of Sciences. All rights reserved.
英文关键词	Bose–Einstein condensation; Excitonic insulator; Ferroelectricity; First-principles many-body perturbation theory; Two-dimensional materials
语种	英语
scopus关键词	article; dipole; phonon
来源期刊	Proceedings of the National Academy of Sciences of the United States of America
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/180103
作者单位	Consiglio Nazionale delle Ricerche - Istituto Nanoscienze, Modena, 41125, Italy; Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università degli Studi di Modena e Reggio Emilia, Modena, 41125, Italy
推荐引用方式 GB/T 7714	Samaneh Ataei S.,Varsano D.,Molinari E.,et al. Evidence of ideal excitonic insulator in bulk MoS2 under pressure[J],2021,118(13).
APA	Samaneh Ataei S.,Varsano D.,Molinari E.,&Rontani M..(2021).Evidence of ideal excitonic insulator in bulk MoS2 under pressure.Proceedings of the National Academy of Sciences of the United States of America,118(13).
MLA	Samaneh Ataei S.,et al."Evidence of ideal excitonic insulator in bulk MoS2 under pressure".Proceedings of the National Academy of Sciences of the United States of America 118.13(2021).