Thermodynamics and Phase Diagram of High Temperature Superconductors

TL;DR

This paper develops a thermodynamic framework for high-temperature superconductors, accounting for amplitude and phase fluctuations, and aligns well with experimental data on cuprates' specific heat and magnetic susceptibility.

Contribution

It introduces a comprehensive thermodynamic model that distinguishes between amplitude and phase fluctuations in the pseudogap regime of cuprates, providing quantitative agreement with experiments.

Findings

Phase correlations extend up to temperature T_φ near the superconducting region.

Above T_φ, the pseudogap is governed solely by amplitude fluctuations.

The pseudogap energy scale correlates with the average amplitude above T_c.

Abstract

Thermodynamic quantities are derived for superconducting and pseudogap regimes by taking into account both amplitude and phase fluctuations of the pairing field. In the normal (pseudogap) state of the underdoped cuprates, two domains have to be distinguished: near the superconducting region, phase correlations are important up to the temperature $T_\phi$. Above $T_\phi$, the pseudogap region is only determined by amplitudes, and phases are uncorrelated. Our calculations show excellent quantitative agreement with specific heat and magnetic susceptibility experiments on cuprates. We find that the mean field temperature $T_0$ has a similar doping dependence as the pseudogap temperature $T^*$, whereas the pseudogap energy scale is given by the average amplitude above $T_c$.