Phase diagram in 2D Fr\"ohlich model of metal at arbitrary carrier density: pseudogap versus doping

TL;DR

This paper explores a 2D fermion system with phonon-mediated attraction, revealing a pseudogap phase with finite order parameter magnitude but random phase, which exists at low carrier densities and may relate to high-temperature superconductor behavior.

Contribution

It introduces the concept of an 'abnormal normal' pseudogap phase in the 2D Fröhlich model, highlighting its dependence on carrier density and potential relevance to high-temperature superconductors.

Findings

Existence of a pseudogap phase at low carrier density.

Pseudogap phase shrinks with increasing doping.

Relevance to high-temperature superconductor phenomena.

Abstract

It is shown that in 2D system of the fermions with simplest indirect boson-induced attraction (through the Einstein phonon exchange as an example) along with the normal and superconducting phases there arises a new (called "abnormal normal" or pseudogap) one where the absolute value of the order parameter is finite but its phase is a random quantity. It is important that this new phase really exists at low carriers density only, i.e. it shrinks when doping increases. The relevance of the results obtained with dependence of pseudogap on doping in high-temperature superconductors is speculated.