Multiband Superconductivity in the Heavy Fermion Compound $\mathrm{Pr}{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$

The thermal conductivity of the heavy fermion superconductor $\mathrm{Pr}{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$ was measured down to $T_c/40$ throughout the vortex state. At lowest temperatures and for magnetic fields $H\approx 0.07H_{c2}$, already 40% of the normal state thermal conductivity is restored. This behavior (similar to that observed in ${\mathrm{MgB}}_2$) is a clear signature of multiband superconductivity in this compound.

Figure 1

$\kappa (T)/T$ at different fields. The anomaly at $T\approx 1\mathrm{K}$ is rapidly suppressed under magnetic fields. Solid line: pure $\kappa /T=aT$ law valid in zero field below 0.2 K. Arrows: $T_c(H)$. Inset: test of the Wiedemann-Franz law.

Figure 2

$\kappa (H)$: Field dependence of $\kappa$: at about $T_c/2$, it may arise from the strong decrease of the “1 K anomaly” (see Fig. 1), whereas at low temperatures, the increase signs MBSC (see Fig. 3). Arrows: $H_{c2}(T)$.

Figure 3

Low temperature behavior of $\kappa (H)$ in a conventional one band superconductor (Nb [37]), ${\mathrm{UPt}}_3$ [32], ${\mathrm{MgB}}_2$ [27], and our own data on $\mathrm{Pr}{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$, adapted from 27. The comparison between ${\mathrm{MgB}}_2$ and $\mathrm{Pr}{\mathrm{Os}}_4{\mathrm{Sb}}_{12}$ is striking, and supports two-band superconductivity in this system.

Figure 4

Squares: $R_c^e$ of one of the two contacts between thermometer and sample (both show the same behavior). By contrast, $R_c^{\mathrm{th}}$ (circles, here multiplied by $L_{0}T$) is strongly diverging at low temperature in zero field, and highly field dependent. Lines are calculated from expression (1) for each field. On this graph, the thermal leak due to the Kevlar suspension remains always above $10\Omega$.