Abstract
We present an atomic resolution scanning tunneling spectroscopy study of superconducting single crystals in magnetic fields up to 9 T. At zero field, a single gap with coherence peaks at is observed in the density of states. At 9 and 6 T, we image a disordered vortex lattice, consistent with isotropic, single flux quantum vortices. Vortex locations are uncorrelated with strong-scattering surface impurities, demonstrating bulk pinning. The vortex-induced subgap density of states fits an exponential decay from the vortex center, from which we extract a coherence length , corresponding to an upper critical field .
- Received 29 October 2008
DOI:https://doi.org/10.1103/PhysRevLett.102.097002
©2009 American Physical Society