Band-Resolved Superconducting Gaps via the Thermal Hall Effect in CeRu2

Abstract

Standard bulk probes of multiband superconductors cannot assign pairing gaps to specific electron or hole Fermi surfaces. Here we show that thermal Hall transport ($κ_{xy}$), constrained by specific heat and normal-state magnetotransport, resolves this ambiguity in the compensated heavy-fermion superconductor CeRu$_2$. Fixing the gap magnitudes ($Δ_e/k_B\approx 13$K, $Δ_h/k_B\approx 8$K) and band mobilities completely determines the electronic degrees of freedom in $κ_{xx}$ and $κ_{xy}$. A low-field sign reversal in $κ_{xy}$ places the larger gap on the heavy Ce $4f$ electron sheets and the smaller on the hole sheets.