Anisotropic electrical resistivity of the magnetic heavy-fermion superconductorURu2Si2

Electrical-resistivity measurements ρ(T,H) on single-crystal ${\mathrm{URu}}_2$ ${\mathrm{Si}}_2$ have been performed between 0.3 and 300 K in fields up to 7 T. ρ(T) is highly anisotropic with the 300-K values parallel to the a and c axes differing by a factor of 2. Both directions exhibit a dρ/dT<0 down to 80 K, followed by a steep decrease in ρ below 50 K. An upper antiferromagnetic transition is clearly discerned by a ‘‘Cr-like’’ anomaly at ≊17 K which also marks the onset of a strong, positive ρ(H). Below 4 K ρ(T) is isotropic and goes to zero at the superconducting transition $T_c$=0.8 K.