Gap fluctuations, Cooper pairs with finite center-of-mass momentum, and suppression of superconductivity in inhomogeneous systems with dopant superpuddles agglomerates

TL;DR

This paper investigates how inhomogeneous dopant superpuddles in granular superconductors affect Cooper pairing, leading to finite momentum pairs, suppressed superconductivity, and amplitude fluctuations, especially relevant for high-temperature cuprates.

Contribution

It introduces a theoretical framework showing that dopant superpuddles induce finite center-of-mass momentum in Cooper pairs, disrupting superconductivity in inhomogeneous systems.

Findings

Finite momentum Cooper pairs break the pairing channel.

Superpuddles cause amplitude fluctuations in the superconducting gap.

Disorder and inhomogeneity reduce the critical temperature.

Abstract

Spatially extended aggregates of dopants are ubiquitous in a plethora of granular superconductors, forming a droplet network that is very important to their characterization and to the description of their superconducting properties. At the same time, one of the most studied classes of superconducting materials are the high-temperature superconductors, where special attention is given to the hole-doped cuprates, where the carrier concentration is controlled by the amount of interstitial oxygen dopants. In this context, the formation of spatially inhomogeneous aggregates of interstitial oxygen atoms, in the form of nanosized superpuddles, is not only relevant, but also a subject of intense recent experimental and theoretical surveys. Following these efforts, in this work we investigate the consequences of the presence of networks of inhomogeneously distributed dopant superpuddles on the superconducting state. Starting from the inhomogeneous extended disordered background brought by the network of superpuddles, we demonstrate, with the aid of an effective interaction between electrons mediated by the local vibrational degrees of freedom of each puddle, that the Cooper pairs arising from an attractive interaction in an inhomogeneous medium have a finite center-of-mass momentum, $\mathbf{p}$, that breaks up the Cooper channel. Furthermore, we derive an analytical expression for the amplitude of the superconducting gap, $\Delta_{\mathbf{k}}$, in terms of disorder and finite center-of-mass momentum and show that amplitude fluctuations are induced in the superconducting state by the presence of the superpuddles, where both the gap and the critical temperature are reduced by disorder and finite momentum pairs. Finally, we discuss our findings in the context of synchronized networks of superconducting oxygen nano-puddles in cuprates and in other granular superconducting systems.