Collective amplitude mode fluctuations in a flat band superconductor

TL;DR

This paper investigates amplitude mode fluctuations in a flat band superconductor model, revealing large fluctuation effects that challenge mean-field theory and suggest strong correlations.

Contribution

It provides a microscopic derivation of Ginzburg-Landau theory for a flat band superconductor with unique fluctuation behavior.

Findings

Large fluctuation contributions to heat capacity.

Mean-field theory becomes inaccurate due to strong correlations.

Amplitude mode gap vanishes, indicating critical fluctuations.

Abstract

We study the fluctuations of the amplitude (i.e. the Higgs-Anderson) mode in a superconducting system of coupled Dirac particles proposed as a model for possible surface or interface superconductivity in rhombohedral graphite. We show that the absence of Fermi energy and vanishing of the excitation gap of the collective amplitude mode in the model leads to a large fluctuation contribution to thermodynamic quantities such as the heat capacity. As a consequence, the mean-field theory becomes inaccurate indicating that the interactions lead to a strongly correlated state. We also present a microscopic derivation of the Ginzburg-Landau theory corresponding to this model.