Role of electron-phonon coupling in excitonic insulator candidate Ta2NiSe5

Abstract

Electron-hole bound pairs, or excitons, are common excitations in semiconductors. They can spontaneously form and ``condense'' into a new insulating ground state -- the so-called excitonic insulator -- when the energy of electron-hole Coulomb attraction exceeds the band gap. In the presence of electron-phonon coupling, a periodic lattice distortion often concomitantly occurs with this exciton condensation. However, similar structural transition can also be induced by electron-phonon coupling itself, therefore hindering the clean identification of bulk excitonic insulators based on reductionistic reasoning (e.g. which instability is the ``driving force'' of the phase transition). Using high-resolution synchrotron x-ray diffraction and angle-resolved photoemission spectroscopy techniques, we identify key electron-phonon coupling effects in a leading excitonic insulator candidate Ta2NiSe5. These include an extensive unidirectional lattice fluctuation and an electronic pseudogap in the normal state, as well as a negative electronic compressibility in the charge-doped broken-symmetry state. In combination with first principles and model calculations, we determine a minimal lattice model and the corresponding interaction parameters that capture the experimental observations. More importantly, we show how the Coulomb and electron-phonon coupling effects can be separated on the level of lattice model, and demonstrate a general framework beyond the reductionist approach in the investigation of correlated systems with intertwined orders.

18 pages, 12 + 4 figures

References in corpus (17)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Theory of Intertwined Orders in High Temperature Superconductors
• Nonthermal pathways to ultrafast control in quantum materials
• Classification of Charge Density Waves Based on Their Nature
• Pseudogap and charge density waves in two dimensions
• Excitonic Bose-Einstein condensation in Ta2NiSe5 above room temperature
• Anomalously Strong Near-Neighbor Attraction in Doped 1D Cuprate Chains
• Electron-Phonon Coupling from $\text{Ab Initio}$ Linear-Response Theory within the $GW$ Method: Correlation-Enhanced Interactions and Superconductivity in Ba${}_{1-x}$K${}_x$BiO${}_3$
• Photo-induced enhancement of excitonic order
• Photoinduced multistage phase transitions in Ta2NiSe5
• Spectroscopic evidence for negative electronic compressibility in a quasi-three-dimensional spin-orbit correlated metal
• Crossed Luttinger Liquid Hidden in a Quasi-two-dimensional Material η-Mo4O11
• Disentangling lattice and electronic instabilities in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ by nonequilibrium spectroscopy
• Revealing the Coulomb interaction strength in a cuprate superconductor
• Exciton dynamics uncovering electron fractionalization in superconducting cuprates
• Ultrafast charge carrier and exciton dynamics in an excitonic insulator probed by time-resolved photoemission spectroscopy
• Detecting photoelectrons from spontaneously formed excitons

Cited by in corpus (13)

• A New Era of Excitonic Insulators
• Spontaneous gap opening and potential excitonic states in an ideal Dirac semimetal Ta${}_2$Pd${}_3$Te${}_5$
• Evidence for an Excitonic Insulator State in Ta${}_2$Pd${}_3$Te${}_5$
• Signatures of Mode-Resolved, Nonlocal Electron-Phonon Coupling in Two-Dimensional Spectroscopy
• Entanglement Witness for Indistinguishable Electrons using Solid-State Spectroscopy
• Persistence of charge ordering instability to Coulomb engineering in the excitonic insulator candidate TiSe${}_2$
• Detecting Thermodynamic Phase Transition via Explainable Machine Learning of Photoemission Spectroscopy
• Anomalous phonon Grüneisen parameters in semiconductor Ta${}_2$NiS${}_5$
• Gate tuning of coupled electronic and structural phase transition in atomically thin Ta${}_2$NiSe${}_5$
• Strong long-wavelength electron-phonon coupling in Ta${}_2$Ni(Se,S)${}_5$
• Unveiling Excitonic Insulator Signatures in Ta${}_2$NiSe${}_5$
• Excitons and Optical Response in Excitonic Insulator Candidate TiSe${}_2$
• Light Control of Triplet Pairing in Correlated Electrons with Mixed-Sign Interactions