Incoherent superconductivity well above $T_c$ in high-$T_c$ cuprates - harmonizing the spectroscopic and thermodynamic data

TL;DR

This paper demonstrates that the energy gap observed above the critical temperature in high-$T_c$ cuprates is due to incoherent superconducting correlations, not a pseudogap, by fitting thermodynamic and spectroscopic data with a temperature-dependent pair-breaking model.

Contribution

It provides a unified explanation for spectroscopic and thermodynamic data in cuprates, clarifying the nature of the gap above $T_c$ as incoherent superconductivity rather than a pseudogap.

Findings

The specific heat and superfluid density data are explained by a temperature-dependent pair-breaking model.

Spectroscopic spectra are simultaneously described using the same pairing and pair-breaking parameters.

The gap above $T_c$ is attributed to incoherent superconducting correlations, not a competing pseudogap.

Abstract

Cuprate superconductors have long been known to exhibit an energy gap that persists high above the superconducting transition temperature ($T_c$). Debate has continued now for decades as to whether it is a precursor superconducting gap or a pseudogap arising from some competing correlation. Failure to resolve this has arguably delayed explaining the origins of superconductivity in these highly complex materials. Here we effectively settle the question by calculating a variety of thermodynamic and spectroscopic properties, exploring the effect of a temperature-dependent pair-breaking term in the self-energy in the presence of pairing interactions that persist well above $T_c$. We start by fitting the detailed temperature-dependence of the electronic specific heat and immediately can explain its hitherto puzzling field dependence. Taking this same combination of pairing temperature and pair-breaking scattering we are then able to simultaneously describe in detail the unusual temperature and field dependence of the superfluid density, tunneling, Raman and optical spectra, which otherwise defy explanation in terms a superconducting gap that closes conventionally at $T_c$. These findings demonstrate that the gap above $T_c$ in the overdoped regime likely originates from incoherent superconducting correlations, and is distinct from the competing-order "pseudogap" that appears at lower doping.