Diving into the vortex
| Date/Time: | Thursday, 09 Mar 2017 from 4:10 pm to 5:00 pm |
|---|---|
| Location: | Physics 3 |
| Phone: | 515-294-7377 |
| Channel: | College of Liberal Arts and Sciences |
| Actions: | Download iCal/vCal | Email Reminder |
Very low temperature Scanning Tunneling Microscopy STM probes the
superconducting density of states as a function of the position. Since
the seminal experiments by Hess et al in Bell labs during the late
eighties, STM has been used to image vortex lattices in many different
compounds. The spatial resolution goes well below the superconducting
coherence length, so that the superconducting properties of the vortex
core can be imaged too. In a simple superfluid, a vortex consists of a
line where the superfluid density vanishes and of quantized superfluid
circulation around it. The rotation occurs exactly at the vortex center.
In a superconductor, we can also consider that the Cooper pair
wavefunction vanishes exactly at the center of the vortex, varying on a
scale of order of the superconducting coherence length. However, STM
images typically show the density of states due to Caroli de Gennes
Matricon localized states that appear inside the vortex core. This was
first observed by Hess et al and has remained one of the mainstreams of
research in STM in superconductors. While it has certainly lead to much
understanding of the localized states, it has been until now notoriously
difficult to extract simple length scales from the images, in particular
the superconducting coherence length. Here I will present recent efforts
in leaving the mainstream that help better understand STM images of
vortices. I will show results in different materials, from a simple
isotropic s-wave superconductor as Bi2Pd, to the recent 1144 pnictides,
passing through the much studied NbSe2. Vortices in tilted magnetic
fields provide some new surprises which I will also discuss.