Abstract
We use quasiparticle tunneling across grain boundary junctions to probe the superconducting state and its disappearance with increasing temperature and magnetic field. A zero bias conductance peak due to zero energy surface Andreev bound states is a clear signature of the phase coherence of the superconducting state. Hence, such a peak must disappear at or below the upper critical field . For this approach sets a lower bound for which is substantially higher than reported previously. The method of probing the superconducting state via Andreev bound states should also be applicable to other cuprate superconductors.
- Received 17 September 2007
DOI:https://doi.org/10.1103/PhysRevLett.100.227001
©2008 American Physical Society