Day / Time
Date(s) - 16/02/2016
13 h 00 min - 14 h 30 min
Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center, Universidad Autónoma de Madrid
The scanning tunneling microscope (STM) is used to view the spatial dependence of low energy electronic excitations—resulting from charge and/or spin correlations—that produce many interesting phenomena in condensed matter physics. To this end, STMs have to be operated under extreme conditions such as low temperatures and high magnetic fields. Recent technical advances have opened the door to microscopy studies at these extreme conditions. Here I will focus on STM made in dilution refrigeration temperatures and show insight obtained by making vivid images of superconducting vortices, obtained by measuring the spatial dependence of the superconducting density of states. I will describe two aspects of the imaging experiments, the vortex cores viewed with atomic resolution and the behaviour of the lattice as a whole viewed at micron length scales. The vortex core is a unique system, a fingerprint of the electronic correlations of each superconducting material, with its shape and size showing anisotropy of Cooper pairs and superconducting excitations. By viewing many vortices one by one, we can also understand the collective behaviour of the vortex lattice. Here I will discuss an order-disorder transition driven by non-thermal (zero temperature) modifications of intervortex interactions induced by increasing magnetic field or vortex density. By analyzing images carefully, we can make a rather complete statistical analysis to quantify the critical behaviour of the order-disorder transition. We find that one-dimensional nanostructuration favors the ordered hexagonal lattice in a large range of magnetic fields.
Work supported by Spanish MINECO, CIG Marie Curie grant, Axa Research Fund and FBBVA.