Superconductivity in the Cuprates: Deduction of Mechanism for D-Wave Pairing Through Analysis of ARPES

TL;DR

This paper uses ARPES data to analyze the pairing mechanism in cuprate superconductors, concluding that antiferromagnetic fluctuations are unlikely the cause, while loop-current fluctuations could explain the observed d-wave pairing.

Contribution

The study provides a quantitative analysis linking ARPES data to the pairing mechanism, ruling out AFM fluctuations and supporting loop-current fluctuations as the origin of d-wave superconductivity in cuprates.

Findings

ARPEs data shows the normal self-energy function is nearly isotropic.

AFM fluctuations with small correlation length cannot produce observed pairing.

Loop-current fluctuations are consistent with the observed pairing and normal self-energy.

Abstract

In the Eliashberg integral equations for d-wave superconductivity, two different functions $(\alpha^2 F)_n(\omega, \theta)$ and $(\alpha^2 F)_{p,d}(\omega)$ determine, respectively, the "normal" and the "pairing" self-energies. We present a quantitative analysis of the high-resolution laser based ARPES data on the compound Bi-2212 to deduce the function$(\alpha^2 F)_n(\omega, \theta)$. Besides its detailed $\omega$ dependence, we find the remarkable result that this function is nearly independent of $\theta$ between the ($\pi,\pi$)-direction and 25 degrees from it. Assuming that the same fluctuations determine both the normal and the pairing self-energy, we ask what theories give the function $(\alpha^2 F)_{p,d}(\omega)$ required for the d-wave pairing instability at high temperatures as well as the deduced $(\alpha^2 F)_n(\theta, \omega)$. We show that the deduced $(\alpha^2 F)_n(\theta, \omega)$ can only be obtained from Antiferromagnetic (AFM) fluctuations if their correlation length is smaller than a lattice constant. Using $(\alpha^2 F)_{p,d}(\omega)$ consistent with such a correlation length and the symmetry of matrix-elements scattering fermions off AFM fluctuations, we calculate $T_c$ an show that AFM fluctuations are excluded as the pairing mechanism for d-wave superconductivity in cuprates. We also consider the quantum-critical fluctuations derived microscopically as the fluctuations of the observed loop-current order discovered in the under-doped cuprates. We show that their frequency dependence and the momentum dependence of their matrix-elements to scatter fermions are consistent with the $\theta$ and $\omega$ dependence of the deduced $(\alpha^2 F)_n(\omega, \theta)$. The pairing kernel $(\alpha^2 F)_{p,d}(\omega)$ calculated using the experimental values in the Eliashberg equation gives $d-wave$ instability at $T_c$ comparable to the experiments.