Phases ofURu2Si2

The tetragonal heavy-fermion system ${\mathrm{URu}}_2$ ${\mathrm{Si}}_2$ may well be an unconventional superconductor, as evidenced by its upper critical field and its low-temperature thermodynamic properties. Under the assumption that it belongs to the E representation of the ${\mathit{D}}_{4\mathit{h}}$ point group, we enumerate the phase diagrams which are possible in the H-T plane. We take into account the possible coupling of superconductivity to the antiferromagnetic order parameter.