Evidence of ideal excitonic insulator in bulk MoS2 under pressure
arXiv:2011.02380 · doi:10.1073/pnas.2010110118
Abstract
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.
References in corpus (26)
- Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
- Phonons and related properties of extended systems from density-functional perturbation theory
- Advanced capabilities for materials modelling with Quantum ESPRESSO
- Optimized norm-conserving Vanderbilt pseudopotentials
- Yambo: an \textit{ab initio} tool for excited state calculations
- Bose-Einstein Condensation of Excitons in Bilayer Electron Systems
- Many-body perturbation theory calculations using the yambo code
- Signatures of exciton condensation in a transition metal dichalcogenide
- Spontaneous Coherence in a Cold Exciton Gas
- Exciton Condensation and Perfect Coulomb Drag
- Spontaneous exciton condensation in 1T-TiSe2: a BCS-like approach
- Theory of Electronic Ferroelectricity
- Structure change, layer sliding, and metallization in high-pressure MoS
- Coherent Order Parameter Oscillations in the Ground State of the Excitonic Insulator Ta2NiSe5
- High pressure effect on structure, electronic structure and thermoelectric properties of MoS
- Interactions and superconductivity in heavily doped MoS2
- Electron-Phonon Coupling Mode in Excitonic Insulator
- Carbon nanotubes as excitonic insulators
- Phase Diagram of Electron Doped Dichalcogenides
- Excitonic and lattice contributions to the charge density wave in 1T-TiSe revealed by a phonon bottleneck
- Quantized Vortices and Four-Component Superfluidity of Semiconductor Excitons
- Evidence of ideal excitonic insulator in bulk MoS2 under pressure
- Nontrivial Metallic State of Molybdenum Disulfide
- Effects of Disorder on the Transport of Collective Modes in an Excitonic Condensate
- Coherent exciton transport in semiconductors
- Anharmonic melting of the charge density wave in single-layer TiSe2
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- First-principles design of excitonic insulators: A review
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