Pseudogap in high-temperature superconductors from realistic Fr\"ohlich and Coulomb interactions

TL;DR

This paper investigates the pseudogap phenomenon in high-temperature superconductors by modeling the interplay of Coulomb and electron-phonon interactions through a polaronic $t$-$J_p$-$ ilde{U}$ framework, revealing a normal state pseudogap without preexisting order.

Contribution

It introduces a charged Bose-Fermi mixture model based on the polaronic $t$-$J_p$-$ ilde{U}$ framework to explain the pseudogap in high-temperature superconductors.

Findings

Presence of a pseudogap in the normal state due to a band gap between bipolarons and unpaired polarons.

Suppression of spin susceptibility, specific heat, and tunneling conductance at low temperatures.

Normal state pseudogap arises without assuming preexisting orders or broken symmetries.

Abstract

It has been recently shown that the competition between unscreened Coulomb and Fr\"{o}hlich electron-phonon interactions can be described in terms of a short-range spin exchange $J_p$ and an effective on-site interaction $\tilde{U}$ in the framework of the polaronic $t$-$J_p$-$\tilde{U}$ model. This model, that provides an explanation for high temperature superconductivity in terms of Bose-Einstein condensation (BEC) of small and light bipolarons, is now studied as a charged Bose-Fermi mixture. Within this approximation, we show that a gap between bipolaron and unpaired polaron bands results in a strong suppression of low-temperature spin susceptibility, specific heat and tunneling conductance, signaling the presence of normal state pseudogap without any assumptions on preexisting orders or broken symmetries in the normal state of the model.