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

Abstract

High magnetic fields up to 105 T have been utilized in deriving the upper critical field $B_{c2}$ of LaFeAsO${}_{1-x}$H${}_x$ throughout whole temperatures below $T_{\mathrm{c}}$. Resistivity measurements demonstrate that $B_{c2}$ 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.