hc/e Periodicity in loops of nodal superconductors

A superconducting state in a multiply connected geometry is characterized by the center of mass momentum q of a Cooper pair q=0 in the ground state of the standard BCS theory without magnetic field. Here we consider superconducting loops threaded by a magnetic flux. In these systems the ground state has a pair momentum q equal to the number of superconducting flux quanta hc/2e threading the loop. For unconventional superconductors, the ground state is different for even and odd numbers of flux quanta and, consequently, their physical properties are hc/e rather than hc/2e periodic.