Partially gapped Fermi surface in the heavy-electron superconductor ${\mathrm{URu}}_2$${\mathrm{Si}}_2$

Transport, thermal, and magnetic data for the heavy electron system ${\mathrm{URu}}_2$${\mathrm{Si}}_2$ indicate that a charge- or spin-density-wave transition opens an energy gap of ∼11 meV over a portion of the Fermi surface below ${\mathrm{T}}_0$≊17.5 K and demonstrate that bulk superconductivity occurs below ${\mathrm{T}}_{\mathrm{c}}$≊1.5 K. The pressure dependences of ${\mathrm{T}}_0$ and ${\mathrm{T}}_{\mathrm{c}}$ support this interpretation. The unusually large initial slope of the upper critical magnetic field (9.2 T/K) is consistent with the high values of the electronic-specific-heat coefficient and the electrical resistivity.