Distinctive Doping Dependence of Upper Critical Field in Iron-Based Superconductor LaFeAsO$_{1-x}$H$_{x}$

TL;DR

This study investigates the upper critical field behavior in LaFeAsO$_{1-x}$H$_x$ superconductors under high magnetic fields, revealing different pairing symmetries and interactions in two doping regimes.

Contribution

It provides the first detailed analysis of the doping-dependent upper critical field and pairing symmetry in LaFeAsO$_{1-x}$H$_x$ using high magnetic field measurements.

Findings

Different $B_{c2}$ behaviors in SC1 and SC2 samples.

SC1 fits a two-band s-wave model with repulsive intraband interactions.

SC2 suggests non-s-wave pairing with attractive intraband interactions.

Abstract

High magnetic fields up to 105 T have been utilized in deriving the upper critical field $B_{\rm c2}$ of LaFeAsO$_{1-x}$H$_x$ throughout whole temperatures below $T_{\rm c}$. Resistivity measurements demonstrate that $B_{\rm c2}$ behaves differently in samples with $x = 0.12$ (SC1) from those with 0.32 (SC2). In SC1, the two-band model assuming the $s$-wave pairing gives a good fitting with repulsive intraband interaction and dominant interband coupling. In SC2, we have to assume attractive intraband interaction with weak interband coupling, which in fact suggests a non-$s$-wave pairing in view of the strong Coulomb repulsion. These results support the possibility that SC1 and SC2 have different pairing symmetries.