The sign and profile of the thermal Hall conductivity κxy​ gives
important insights into the gap structure of multi-band superconductors. With
this perspective, we have investigated κxy​ and the thermal
conductivity κxx​ in Ba1−x​Kx​Fe2​As2​ which display large
peak anomalies in the superconducting state. The anomalies imply that a large
hole-like quasiparticle (qp) population exists below the critical temperature
Tc​. We show that the qp mean-free-path inferred from κxx​
reproduces the observed anomaly in κxy​, providing a consistent
estimate of a large qp population. Further, we demonstrate that the hole-like
signal is 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.Comment: 5 pages, 4 figures. Orientation significantly updated from previous
(0811.4668v1) reflecting new theoretical understanding of experimental
results and physical implications. Introduction, discussion, and figures
updated including additional figure for model calculatio