Fluctuation Diamagnetism in Two-Band Superconductors

TL;DR

This paper investigates how two-band superconductors exhibit enhanced fluctuation diamagnetism near the critical temperature, using a phenomenological Ginzburg-Landau approach, to explain recent experimental observations in FeSe.

Contribution

It introduces a theoretical analysis of fluctuation diamagnetism in two-band superconductors, highlighting the role of multiple fluctuation modes in enhancing diamagnetic response.

Findings

Two distinct fluctuation modes can enhance diamagnetism in two-band systems.

The model qualitatively explains the large diamagnetism observed in FeSe.

Enhancement is significant but not quantitatively matching experimental data.

Abstract

Anomalously large fluctuation diamagnetism around the superconducting critical temperature has been recently observed on iron selenide (FeSe) [S. Kasahara et al., unpublished]. This indicates that superconducting fluctuations (SCFs) play a more significant role in FeSe, which supposedly has two-band structure, than in the familiar single-band superconductors. Motivated by the data in FeSe, SCF-induced diamagnetism is examined in a two-band system, on the basis of a phenomenological approach with a Ginzburg-Landau functional. The obtained results indicate that the SCF-induced diamagnetism may be more enhanced than that in a single-band system due to the existence of two distinct fluctuation modes. Such enhancement of diamagnetism unique to a two-band system seems consistent with the large diamagnetism observed on FeSe, though still far from a quantitative agreement.