Evidence of d-wave Superconductivity in K_(1-x)Na_xFe_2As_2 (x = 0, 0.1) Single Crystals from Low-Temperature Specific Heat Measurements

TL;DR

This study provides evidence for d-wave superconductivity in K_(1-x)Na_xFe_2As_2 single crystals through low-temperature specific heat measurements, revealing a nodal gap structure consistent with theoretical models.

Contribution

It demonstrates the presence of d-wave pairing symmetry in these materials using specific heat data and theoretical analysis, advancing understanding of their superconducting nature.

Findings

Large T^2 specific heat contributions indicating nodal gaps

Square root field dependence of specific heat in the superconducting state

Estimated gap amplitude matches Eliashberg theory predictions

Abstract

From the measurement and analysis of the specific heat of high-quality K_(1-x)Na_xFe_2As_2 single crystals we establish the presence of large T^2 contributions with coefficients alpha_sc ~ 30 mJ/mol K^3 at low-T for both x=0 and 0.1. Together with the observed square root field behavior of the specific heat in the superconducting state both findings evidence d-wave superconductivity on almost all Fermi surface sheets with an average gap amplitude of Delta_0 in the range of 0.4 - 0.8 meV. The derived Delta_0 and the observed T_c agree well with the values calculated within the Eliashberg theory, adopting a spin-fluctuation mediated pairing in the intermediate coupling regime.