Pseudogap phase formation in the crossover from Bose-Einstein condensation to BCS superconductivity

TL;DR

This paper derives a phase diagram for a 2D metal showing various phases including pseudogap and superconducting states, analyzing transitions and properties relevant to high-$T_c$ superconductors.

Contribution

It introduces a detailed phase diagram for 2D metals with variable carrier density, highlighting the pseudogap phase and transition temperatures, connecting theory with high-$T_c$ superconductor features.

Findings

Identification of distinct phases including pseudogap and superconducting phases.

Calculation of transition temperatures between phases.

Analysis of chemical potential and susceptibility behavior.

Abstract

A phase diagram for a 2D metal with variable carrier density has been derived. It consists of a normal phase, where the order parameter is absent; a so-called ``abnormal normal'' phase where this parameter is also absent but the mean number of composite bosons (bound pairs) exceeds the mean number of free fermions; a pseudogap phase where the absolute value of the order parameter gradually increases but its phase is a random value, and finally a superconducting (here Berezinskii-Kosterlitz-Thouless) phase. The characteristic transition temperatures between these phases are found. The chemical potential and paramagnetic susceptibility behavior as functions of the fermion density and the temperature are also studied. An attempt is made to qualitatively compare the resulting phase diagram with the features of underdoped high-$T_{c}$ superconducting compounds above their critical temperature.