Suppression of fluctuations in a two-band superconductor with a quasi-1D band

TL;DR

This paper investigates how interband coupling in two-band superconductors with a quasi-1D band can suppress thermal fluctuations, allowing the critical temperature to approach its mean-field value across various parameters.

Contribution

It provides a detailed calculation of critical temperatures and demonstrates the robustness of fluctuation suppression via interband coupling in Q1D multiband superconductors.

Findings

Critical temperature T_c remains close to T_c0 over a wide parameter range.

Dimensionality of the higher-dimensional band has minimal impact on fluctuation suppression.

Interband pair-exchange coupling effectively suppresses fluctuations, enhancing T_c.

Abstract

Chain-like structured superconductive materials (such as A_2Cr_3As_3, with A = K, Rb, Cs) exhibit the multiband electronic structure of single-particle states, where coexisting quasi-one-dimensional (Q1D) and conventional higher-dimensional energy bands take part in the creation of the aggregate superconducting condensate. When the chemical potential approaches the edge of a Q1D band in a single-band superconductor, the corresponding mean-field critical temperature increases significantly but the superconductivity is quenched by fluctuations. However, recent investigation has revealed that when a Q1D band is coupled to a higher dimensional one by the interband Cooper-pair transfer, the thermal superconductive fluctuations can be suppressed so that the resulting critical temperature can be close to its mean-field value. In the present work, we calculate the mean-field T_c0 and fluctuation-shifted T_c critical temperatures for a two-band superconductor where a Q1D band coexists with a higher-dimensional band, and investigate how the thermal fluctuations are sensitive to the system parameters. We find that T_c is close to T_c0 in a wide range of microscopic parameters, and even the dimensionality of the higher-dimensional band does not play an essential role. Thus, the screening mechanism for suppressing fluctuations via the pair-exchange coupling between the bands is indeed relevant for a large class of Q1D multiband superconducting materials, encouraging further experiments aimed at reaching larger critical temperatures in such multiband superconductors.