Speaker
Description
We use density matrix renormalization group (DMRG) and variational exact diagonalization (VED) to calculate the single-electron removal spectral weight for the Hubbard-Holstein model at low electron densities. Tuning the strength of the electron-phonon coupling and of the Hubbard repulsion allows us to contrast the results for a liquid of polarons versus a liquid of bipolarons. The former shows spectral weight up to the Fermi energy, as expected for a (uncorrelated) metal. The latter has a gap in its spectral weight, set by the bipolaron binding energy, although this is also a (strongly correlated) metal. This difference suggests that angle-resolved photoemission spectroscopy could be used to identify liquids of pre-formed pairs. Furthermore, we show that the liquid of bipolarons is well approximated by an ensemble of bosons that are hard-core in momentum space, filling the states inside the Fermi sea but otherwise non-interacting [1].
In the second part I will discuss the two-electron removal spectral weight for the Hubbard-Holstein model, starting from the ground-state with two electrons on a one-dimensional chain. We argue that this spectral weight provides a valuable proxy for the intensity of 2e-ARPES processes. Our results show that when contrasted to the (large) signal due to two electrons ejected from two different pairs, the (much
weaker) signal due to two electrons ejected from the same pair (i) is segregated in energy, appearing at a lower binding energy, and (ii) has a very characteristic momentum dependence, with different symmetry than that corresponding to two electrons emitted from two different pairs [2].
[1] K. Kovac, A. Nocera, A. Damascelli, J. Bonca, and M. Berciu, Phys, Rev. Lett. 134, 096502 (2025)
[2] J. Bonca, A. Damascelli, and M. Berciu, in preparation
