Spectral function of a bipolaron coupled to dispersive optical phonons

Kovač, Klemen (author), Bonča, Janez (author)

Using an efficient variational exact diagonalization method, we computed the electron removal spectral function within the framework of the Holstein-Hubbard model containing two electrons with opposite spins coupled to dispersive quantum optical phonons. We focus on how the interplay between the electron-phonon coupling and on-site Coulomb repulsion shapes the spectral function, a quantity directly relevant to angle-resolved photoemission spectroscopy (ARPES). Tuning the strengths of the electron-phonon coupling and the Hubbard interaction allows us to examine the evolution of the spectral properties of the system as it crosses over from a bound bipolaron to separate polarons. We find that phonon dispersion plays an important role: It substantially redistributes the spectral weight across the low- and the high-energy features and controls the emergence and the structure of distinct multiphonon continua. In regimes of strong electron-phonon coupling and low Coulomb repulsion, the spectral function exhibits a broad distribution reflecting bound bipolaronic states. Increasing the Coulomb repulsion weakens bipolaron binding, shifts the primary quasiparticle peak closer to polaronic behavior and confines the spectral weight near the Brillouin-zone center. Our results provide a framework for interpreting ARPES measurements in systems where phonon–mediated attraction competes with direct Coulomb repulsion.

• Language: English
• Keywords: condensed matter physics, quantum physics, optical phonons, polarons, Holstein model, Hubbard model, electron-phonon coupling
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Year: 2025
• Number of pages: Str. 115133-1-115133-12
• Numbering: Vol. 111, iss. 11
• PID: 20.500.12556/RUL-167837
• UDC: 538.9
• ISSN on article: 2469-9950
• DOI: 10.1103/PhysRevB.111.115133
• COBISS.SI-ID: 229057027
• Publication date in RUL: 14.03.2025

Record is a part of a journal

• Title: Physical review
• Publisher: American Physical Society
• ISSN: 2469-9950
• COBISS.SI-ID: 2997348

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: fizika kondenzirane snovi, kvantna fizika, optični fononi, polaroni, Holsteinov model, Hubbardov model, elektronsko-fononska sklopitev

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P1-0044-2022
• Name: Teorija trdnih snovi in statistična fizika