Symmetry of the gap in superconductingURu2Si2

We have modeled the specific heat in the superconducting state of the heavy-fermion compound ${\mathrm{URu}}_2$ ${\mathrm{Si}}_2$, considering all symmetry-allowed gap functions. The best agreement with experiment occurs for a single line of zeroes. In this case there is excellent agreement on the size of the step in specific heat at the critical temperature and good agreement on the power law of the temperature dependence below ${\mathit{T}}_{\mathit{c}}$. Although the strikingly linear dependence of C on ${\mathit{T}}^2$ that is experimentally observed is not simply reproduced in our modeling, it can be approximated by assuming a slightly larger gap amplitude than predicted by weak-coupling theory.