Theory of tunneling spectroscopy in U Pd2 Al3

There is still significant debate about the symmetry of the order parameter in the heavy-fermion superconductor U Pd2 Al3, with proposals for cos (k3), cos (2 k3), sin (k3), and ei sin (k3). Here, we analyze the tunneling spectroscopy of this compound and demonstrate that the experimental results by Jourdan [Nature (London) 398, 47 (1999)] are inconsistent with the last two order parameters, which are expected to show zero-bias conductance peaks. We propose a definitive tunneling experiment to distinguish between the first two order parameters.