Speaker: Janez Bonča, University of Ljubljana

Time: 10:00-11:00am

Location: BRIM 311

Title: Signature of preformed pairs in angle-resolved two-electron coincidence photoemission

Abstract: We employ density matrix renormalization group (DMRG) and variational exact diagonalization (VED) to compute single- and two-electron removal spectra of the Hubbard–Holstein model at low electron densities. By tuning electron–phonon coupling and Hubbard repulsion, we distinguish polaron and bipolaron liquids. While both are metallic, the polaron liquid exhibits spectral weight up to the Fermi energy, whereas the bipolaron liquid shows a gap set by the bipolaron binding energy, suggesting that ARPES can identify liquids of preformed pairs. The bipolaron liquid is well approximated by a gas of hard-core bosons in momentum space [1].

Two-electron coincidence spectra reveal distinct energy and momentum signatures for electrons emitted from the same versus different pairs. These generic fingerprints provide a route to detect pairing and distinguish coherent from incoherent pairs [2].  The pair binding energy can be read off directly from the 2eARPES intensity map when defined as a functiopn of the two distinct frequencies of ejected  photoelectrons. [3]

[1] K. Kovac, A. Nocera,  A.  Damascelli,  J. Bonca, and M. Berciu, Phys. Rev. Lett. 134, 096502 (2025).

[2] J. Bonca,  A.  Damascelli,  M. Berciu, under review.

[3] J. Bonca,  A. Nocera, A.  Damascelli,  M. Berciu, in preparation.