In contrast to almost all anisotropic superconductors, the upper critical field of URu$_{ 2}$Si$_{ 2}$ is larger when the field is oriented along the less conducting direction. We present a study of resistivity and Seebeck coefficient extended down to sub-Kelvin temperature range uncovering a singular case of anisotropy. When the current is injected along the c-axis URu$_{ 2}$Si$_{ 2}$ behaves as a low-density Fermi liquid. When it flows along the a-axis, even in presence of a large field, resistivity remains T-linear down to T$_{ c}$ and the Seebeck coefficient undergoes a sign change at very low temperatures. We conclude that the characteristic energy scale is anisotropic and vanishingly small in the basal plane.
Categories: cond-mat.str-el cond-mat.supr-con