Thermal Hall Conductivity as a Probe of Gap Structure in Multi-band Superconductors: The Case of $ m Ba_{1-x}K_xFe_2As_2$

摘要

The sign and profile of the thermal Hall conductivity $\kappa_{xy}$ givesimportant insights into the gap structure of multi-band superconductors. Withthis perspective, we have investigated $\kappa_{xy}$ and the thermalconductivity $\kappa_{xx}$ in $\rm Ba_{1-x}K_xFe_2As_2$ which display largepeak anomalies in the superconducting state. The anomalies imply that a largehole-like quasiparticle (qp) population exists below the critical temperature$T_c$. We show that the qp mean-free-path inferred from $\kappa_{xx}$reproduces the observed anomaly in $\kappa_{xy}$, providing a consistentestimate of a large qp population. Further, we demonstrate that the hole-likesignal is consistent with a theoretical scenario where despite potentiallylarge gap variations on the electron pockets, the minimal homogeneous gap ofthe superconducting phase resides at a hole pocket. Implications for probingthe gap structure in the broader class of pnictide superconductors arediscussed.