Hydrostatic Pressure-Induced Evolution of the Superconducting Transition Temperature of Bi-2212: Insights from First-Principles Calculations

TL;DR

This study combines first-principles calculations and models to explain how hydrostatic pressure affects the superconducting transition temperature in Bi-2212, revealing a complex interplay of doping and pairing effects.

Contribution

It provides a unified theoretical explanation for the conflicting experimental observations of $T_c$ evolution under pressure in Bi-2212.

Findings

Pressure induces self-doping, increasing hole concentration in CuO$_2$ planes.

Pressure enhances pairing interactions through renormalized hopping and superexchange.

The $T_c$ response to pressure depends on initial doping, explaining experimental discrepancies.

Abstract

High-pressure experiments on Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (Bi-2212) have reported apparently conflicting evolutions of the superconducting transition temperature $T_c$, ranging from weak enhancement to strong suppression and even a proposed second superconducting dome. To clarify the origin of these discrepancies, we combine first-principles density functional theory calculations with a pressure-dependent low-energy bilayer model solved by the slave-boson mean-field method together with a Berezinskii-Kosterlitz-Thouless estimate of phase coherence. Our results show that hydrostatic pressure induces a pronounced self-doping effect in Bi-2212: holes are transferred from the Bi-O charge-reservoir layers to the CuO$_2$ superconducting planes, leading to a systematic increase in the effective CuO$_2$-plane hole concentration $\delta_x$. At the same time, pressure enhances the pairing scale through the renormalization of the hopping and superexchange parameters. As a consequence, the pressure evolution of $T_c$ is governed by the competition between pressure-enhanced pairing and pressure-driven motion along the common $T_c$-$\delta_x$ dome, making $T_c(P)$ highly sensitive to the initial doping state. Even samples with very similar ambient-pressure $T_c$ but slightly different initial doping can therefore display qualitatively different pressure responses. This provides a unified interpretation of a large part of the disparate high-pressure behavior reported for Bi-2212 and suggests that slightly underdoped samples are more favorable than ambient-pressure optimal samples for achieving improved superconducting performance under pressure.