Direct observation of excitonic instability in Ta2NiSe5

Abstract

Coulomb attraction between electrons and holes in a narrow-gap semiconductor or a semimetal is predicted to lead to an elusive phase of matter dubbed 'excitonic insulator'. However, direct observation of such electronic instability remains extremely rare. Here, we report the observation of incipient divergence in the static excitonic susceptibility of the candidate material Ta2NiSe5 using Raman spectroscopy. Critical fluctuations of the excitonic order parameter give rise to quasi-elastic scattering of B2g symmetry, whose intensity grows inversely with temperature toward the Weiss temperature of Tw ~241 K, which is arrested by a structural phase transition driven by an acoustic phonon of the same symmetry at Tc =325 K. Concurrently, a B2g optical phonon becomes heavily damped to the extent that its trace is almost invisible around Tc, which manifests a strong electron-phonon coupling that has obscured the identification of the low-temperature phase as an excitonic insulator for more than a decade. Our result unambiguously reveals the electronic origin of the phase transition.

The data shown in Figs. 1-3 in the previous version were not corrected for the Bose factor. 7 pages, 4 figures

References in corpus (14)

• Vortices and Superfluidity in a Strongly Interacting Fermi Gas
• Inelastic Light Scattering From Correlated Electrons
• Evidence of high-temperature exciton condensation in 2D atomic double layers
• Direct Observation of the Superfluid Phase Transition in Ultracold Fermi Gases
• Excitonic Bose-Einstein condensation in Ta2NiSe5 above room temperature
• Nature of symmetry breaking at the excitonic insulator transition: Ta${}_2$NiSe${}_5$
• Band hybridisation at the semimetal-semiconductor transition of Ta${}_2$NiSe${}_5$ enabled by mirror-symmetry breaking
• Criterion for stability of Goldstone Modes and Fermi Liquid behavior in a metal with broken symmetry
• Non-Coulomb strong electron-hole binding in $T{a}_{2}NiS{e}_5$ revealed by time- and angle-resolved photoemission spectroscopy
• Imaging the coherent propagation of collective modes in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ at room temperature
• Fate of the excitonic insulator in the presence of phonons
• Orthorhombic-to-monoclinic transition in Ta${}_2$NiSe${}_5$ due to a zone-center optical phonon instability
• Phononic soft mode and strong electronic background behavior across the structural phase transition in the excitonic insulator Ta${}_2$NiSe${}_5$ (with Erratum)
• The spontaneous symmetry breaking in Ta${}_2$NiSe${}_5$ is structural in nature

Cited by in corpus (43)

• Imaging the coherent propagation of collective modes in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ at room temperature
• Photoinduced multistage phase transitions in Ta2NiSe5
• Ultrafast melting and recovery of collective order in the excitonic insulator Ta${}_2$NiSe${}_5$
• Evidence of high-temperature exciton condensation in a two-dimensional semimetal
• Photo-induced phase transition and associated time scales in the excitonic insulator Ta${}_2$NiSe${}_5$
• Second order Josephson effect in excitonic insulators
• Lattice dynamics of the excitonic insulator Ta${}_2$Ni(Se${}_{1-x}$S${}_x$)${}_5$
• Role of electron-phonon coupling in excitonic insulator candidate Ta2NiSe5
• Robust high-temperature topological excitonic insulator of transition-metal carbides (MXenes)
• A New Era of Excitonic Insulators
• Disentangling lattice and electronic instabilities in the excitonic insulator candidate Ta${}_2$NiSe${}_5$ by nonequilibrium spectroscopy
• Unveiling the underlying interactions in Ta2NiSe5 from photo-induced lifetime change
• Observation of possible excitonic charge density waves and metal-insulator transitions in atomically thin semimetals
• Anomalous excitonic phase diagram in band-gap-tuned Ta2Ni(Se,S)5
• Spontaneous gap opening and potential excitonic states in an ideal Dirac semimetal Ta${}_2$Pd${}_3$Te${}_5$
• Terahertz parametric amplification as a reporter of exciton condensate dynamics
• Failed excitonic quantum phase transition in Ta${}_2$Ni(Se${}_{1-x}$S${}_x$)${}_5$
• Fermi edge singularity in neutral electron-hole system
• Thermal transport signatures of the excitonic transition and associated phonon softening in the layered chalcogenide Ta${}_2$NiSe${}_5$
• Pressure suppression of the excitonic insulator state in Ta2NiSe5 observed by optical conductivity
• Third-harmonic generation in excitonic insulators
• Theory of time-crystalline behaviour mediated by phonon squeezing in Ta2NiSe5
• Excitonic insulators and Gross-Neveu models
• Collective modes and Raman response in Ta${}_2$NiSe${}_5$
• Collective magnetic Higgs excitation in a pyrochlore ruthenate
• Electronic band structure in pristine and Sulfur-doped Ta${}_2$NiSe${}_5$
• Pseudogap Formation in the Nodal-Line Semimetal NaAlGe
• Detecting photoelectrons from spontaneously formed excitons
• Photo-induced Dynamics of Quasicrystalline Excitonic Insulator
• 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)${}_5$
• Hysteretic Phonons and Quasielastic Response: A Raman Study of Thermal Memory in Two-dimensional CuCrP2S6
• Elastic Soft Mode and Electric Quadrupole Response in Excitonic Insulator Candidate (Ta${}_{0.952}$V${}_{0.048}$)${}_2$NiSe${}_5$: Contribution of Electron-Phonon Interaction
• Quantum coherent states of mass-imbalanced electron-hole system within optical microcavities
• Topological spin-up triplet excitonic condensation in two-dimensional electron-hole systems
• Introduction to High-Temperature Superconductivity for Solid State Chemists
• Dynamical signatures and control of time-reversal breaking in twisted nodal superconductors
• Unveiling Excitonic Insulator Signatures in Ta${}_2$NiSe${}_5$
• Probing the collective excitations of excitonic insulators in an optical cavity
• Ab initio Approach to Collective Excitations in Excitonic Insulators
• Interplay of Rashba spin-orbit coupling and Coulomb interaction in topological spin-triplet excitonic condensates
• Large Kohn anomaly and phonon collapse induced by charge density wave in UPt${}_2$Si${}_2$
• Long-lived relaxation channel and exciton-phonon coupling in Ta2NiSe5 via non-degenerate pump-probe spectroscopy