CMD30 FisMat2023 - Submission - View

Abstract title: Order, criticality, and excitations in the extended Falicov-Kimball model: A case study for the strong excitonic insulator candidate Ta2NiSe5
Submitting author: Holger Fehske
Affiliation: University Greifswald
Affiliation Address: Institute of Physics University Greifswald Felix-Hausdorff-Str. 6 17489 Greifswald Germany
Country: Germany
Other authors and affiliations: Ejima Satoshi (Quantumcomputing-Intiative, Hamburg, Germany), Lange Florian (Zentrum für Nationales Hochleistungsrechnen NHR@FAU, Erlangen, Germany), KanekoTatsuya (RIKEN Center for Emergent Matter Science, Wako, Saitama, Japan), Ohta Yukinori (Department of Physics, Chiba University, Chiba, Japan)
Abstract
We investigate the nature of excitonic  bound states and the emergence of exciton coherence in the one-dimensional half-filled extended Falicov-Kimball model (EFKM) by means of unbiased numerical techniques. The EFKM ground-state phase diagram  exhibits, besides band-insulator and staggered orbital ordered phases, an excitonic insulator (EI) state with power-law correlations. The criticality of the EI state shows up in the von Neumann entropy. The anomalous spectral function and condensation amplitude provide the binding energy and coherence length of the electron-hole pairs which, on their part, point towards a Coulomb interaction driven crossover from BCS-like electron-hole pairing fluctuations to tightly bound excitons.  In a non-equilibrium situation, we demonstrate photoinduced pairing of electron and holes as well as metallization  of the EI. In the latter case, an extra band appears above the Fermi energy after pulse irradiation, indicating an insulator-to-metal quantum phase transition.  For model parameters best suited for Ta2NiSe5 the photoemission spectrum develops a weak but clearly visible two-peak structure around the Fermi momenta k≃±kF, suggesting that Ta2NiSe5 embodies an EI of BCS-like type. At higher temperatures, the leakage of the conduction-electron band beyond the Fermi energy becomes distinct, which might serve as an explanation for the bare non-interacting band structure seen in time- and angle-resolved photoemission spectroscopy experiments.   References: [1] S. Ejima, T. Kaneko, Y. Ohta, and H. Fehske, Order, criticality, and excitations in the extended Falicov-Kimball model, Phys. Rev. Lett. 112, 026401 (2014). [2] S. Ejima, F. Lange, and H. Fehske, Finite-temperature photoemission in the extended Falicov-Kimball model: a case study for Ta2NiSe5,  SciPost Phys.10, 077 (2021). [3] S. Ejima, F. Lange, and H. Fehske, Photoinduced metallization of excitonic insulators, Phys. Rev. B 105, 245126 (2022).