Thermal Transport in the Hidden-Order State of ${\mathrm{URu}}_2{\mathrm{Si}}_2$

We present a study of thermal conductivity in the normal state of the heavy-fermion superconductor ${\mathrm{URu}}_2{\mathrm{Si}}_2$. Ordering at 18 K leads to a steep increase in thermal conductivity and (in contrast with all other cases of magnetic ordering in heavy-fermion compounds) to an enhancement of the Lorenz number. By linking this observation to several other previously reported features, we conclude that most of the carriers disappear in the ordered state and this leads to a drastic increase in both the phononic and electronic mean free path.

Figure 1

Temperature dependence of thermal conductivity of sample 1 for different magnetic fields.

Figure 2

The zero-field Lorenz number normalized to the Sommerfeld value as a function of temperature for sample 1 (solid circles) and sample 2 (open circles).

Figure 3

The field dependence of $\frac{{\kappa }_{xy}}{T}$ at $T=5.5\mathrm{K}$ in sample 2. The solid line represents the field dependence of ${\sigma }_{xy}$ in the same sample multiplied by the Sommerfeld value.

Figure 4

Lattice (${\kappa }_{\mathrm{ph}}$) and electronic (${\kappa }_e$) components of thermal conductivity in sample 1, assuming ${\kappa }_e=L_0\sigma T$ in the whole temperature range.