Thermal Hall conductivity as a probe of gap structure in multiband superconductors: The case of Ba1-xKxFe2As2

The sign and profile of the thermal Hall conductivity kappa(xy) gives important insights into the gap structure of multiband superconductors. With this perspective, we have investigated kappa(xy) and the thermal conductivity kappa(xx) in Ba1-xKxFe2As2 which display large peak anomalies in the superconducting state. The anomalies imply that a large holelike 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 consistent estimate of a large QP population. Further, we demonstrate that the peak structure and holelike signal are consistent with a theoretical scenario where, despite potentially large gap variations on the electron pockets, the minimal homogeneous gap of the superconducting phase resides at a hole pocket. Implications for probing the gap structure in the broader class of pnictide superconductors are discussed.