Fermion zero modes on vortices in chiral superconductors

The energy levels of fermions bound to the vortex core are considered for t he general case of chiral superconductors. There are two classes of chiral superconductivity: in the class I superconducting state the axisymmetric si ngly quantized vortex has the same energy spectrum of bound states as in an s-wave superconductor: E = (n 1/2) omega(0), with integral n. In class II the corresponding spectrum is E = n omega(0) and thus contains a state with exactly zero energy. The effect of a single impurity on the spectrum of bo und states is also considered. For class I the spectrum acquires the double d period Delta E = 2 omega(0) and consists of two equidistant sets of level s, in accordance with A. I. Larkin and Yu. N. Ovchinnikov, Phys. Rev. B 57, 5457 (1998). For the class II states the spectrum is not influenced by a s ingle impurity if the same approximation is applied. (C) 1999 American Inst itute of Physics. [S0021-3640(99)00921-4].