Calorimetric Evidence of Strong-Coupling Multiband Superconductivity in Fe(Te0.57Se0.43) Single Crystal

TL;DR

This study provides calorimetric evidence that the superconductor Fe(Te0.57Se0.43) exhibits strong-coupling multiband superconductivity, characterized by a double-gap structure and significant specific heat jump, indicating intermediate electronic correlations.

Contribution

It presents the first calorimetric analysis of Fe(Te0.57Se0.43), revealing strong-coupling multiband superconductivity with a double-gap model and large specific heat jump.

Findings

Double-gap superconductivity with large gap ratios

Large specific heat jump indicating strong coupling

Magnetic field dependence supports multiband nature

Abstract

We have investigated the specific heat of optimally-doped iron chalcogenide superconductor Fe(Te0.57Se0.43) with a high-quality single crystal sample. The electronic specific heat Ce of this sample has been successfully separated from the phonon contribution using the specific heat of a non-superconducting sample (Fe0.90Cu0.10)(Te0.57Se0.43) as a reference. The normal state Sommerfeld coefficient gamma_n of the superconducting sample is found to be ~ 26.6 mJ/mol K^2, indicating intermediate electronic correlation. The temperature dependence of Ce in the superconducting state can be best fitted using a double-gap model with 2Delta_s(0)/kBTc = 3.92 and 2Delta_l(0)/kBTc = 5.84. The large gap magnitudes derived from fitting, as well as the large specific heat jump of Delta_Ce(Tc)/gamma_n*Tc ~ 2.11, indicate strong-coupling superconductivity. Furthermore, the magnetic field dependence of specific heat shows strong evidence for multiband superconductivity.