Coupled electronic and magnetic excitations in the cuprates and their role in the superconducting transition

TL;DR

This study investigates whether spin fluctuations can explain the pairing mechanism in cuprate high-temperature superconductors by analyzing spectral functions from ARPES data and solving the Bethe-Salpeter equation, finding results consistent with superconductivity.

Contribution

It demonstrates that spin fluctuations can approximately account for the superconducting transition temperature and pairing symmetry in cuprates using a first-principles approach.

Findings

Eigenvalues approach 1 at Tc, indicating a superconducting transition.

Results support spin fluctuations as a mediating mechanism for pairing.

Eigenfunctions exhibit d-wave symmetry consistent with experiments.

Abstract

The formation of Cooper pairs, a bound state of two electrons of opposite spin and momenta by exchange of a phonon [1], is a defining feature of conventional superconductivity. In the cuprate high temperature superconductors, even though it has been established that the superconducting state also consists of Cooper pairs, the pairing mechanism remains intensely debated. Here we investigate superconducting pairing in the Bi2Sr2CaCu2O8+\delta (Bi2212) cuprate by employing spectral functions obtained directly from angle-resolved photoemission (ARPES) experiments as input to the Bethe-Salpeter gap equation. Assuming that Cooper pairing is driven solely by spin fluctuations, we construct the single-loop spin-fluctuation-mediated pairing interaction, and use it to compute the eigenfunctions and eigenvalues of the Bethe-Salpeter equation in the particle-particle channel for multiple Bi2212 samples. The key point of our results is that, as the temperature is reduced, the leading eigenvalue increases upon approaching Tc, reaching a value of approximately 1 at the Tc corresponding to each doping value, indicating a superconducting transition with d-wave eigenfunctions. This suggests that spin fluctuations can approximately account for Tc and, consequently, mediate pairing in the cuprate high temperature superconductors.