Abstract
We show that in ultrasmall superconducting grains any concentration of magnetic impurities or infinitely small orbital effect of magnetic field leads to destruction of the hard gap in the tunneling density of states, and find analytically the exponential tail at low energies. Thus, the tunneling density of states exhibits the “soft gap” behavior. As the energy approaches zero, it vanishes linearly with excitation energy.
- Received 13 December 1999
DOI:https://doi.org/10.1103/PhysRevLett.85.816
©2000 American Physical Society