The vortex lattice viewed by very low temperature scanning tunneling microscopy and spectroscopy
|Date/Time:||Friday, 16 Nov 2012 - Friday, 16 Nov 2012|
|Location:||Room 19 PHYSICS HALL|
|Channel:||Condensed Matter Physics|
During past years we have been developing dilution refrigerator scanning tunneling microscopy to achieve atomic size real space mapping with high energy resolution. I will review the basics of this technique, and present new developments such as local Josephson spectroscopy, Andreev spectroscopy and current drive microscopy, which provide powerful methods to map out the phase and spin of superconducting condensates. I will then focus on measurements in disordered superconducting thin films, where we have followed the vortex lattice at 100 mK from a few vortices to thousands of vortices in the same field of view. We observe vortex re-orientations by vortex pinning in linear surface features at low fields followed by lattice compression which results, at surprisingly low fields, to a cross-over into a disordered phase. The different phases observed in this process can be uniquely characterized thanks to real space observation, and are found to follow perfectly Berezinskii-Kost erlitz-Thouless melting process, within a lattice which is however at its ground state. The disordered high field phase is very peculiar: defects bunch into amorphous areas separated by more "crystalline" regions.