Who: Isabel Guillamon (UAM, Madrid)
Place: Donostia International Physics Center (DIPC). Paseo Manuel de Lardizabal, 4, Donostia
Date: Friday, 6 March 2015, 12:00
Scanning tunneling spectroscopy of the superconducting vortex lattice
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
Scanning tunneling spectroscopy allows imaging the superconducting vortex lattice showing the behaviour of a single vortex up to the collective response of the lattice. Moreover, experiments can be made from very low temperatures up to the upper critical magnetic field providing microscopic insight over the whole phase diagram.
Here I will present a recent work where we have imaged up to several thousands of vortices one by one in a nanostructured superconductor and developed image treatment algorithms that allow characterizing the collective response of the lattice . With these tools, we have studied the influence of quenched random disorder on an ordered two dimensional (2D) vortex lattice.
In 2D systems, theory has proposed that random disorder destroys long-range correlations driving a transition to a glassy state. In this talk, I will discuss new insights into this issue obtained through the direct visualization of the critical behaviour of a 2D superconducting vortex lattice formed in a thin film with a smooth one-dimensional (1D) thickness modulation. By nanofabricating the sample with 1D modulation, we produced controlled random disorder. I will show how the hexagonal lattice starts floating over the nanostructure, and how the floating lattice disorders due to the random disorder. We observed a two-step order-disorder transition mediated by the appearance of dislocations and disclinations and accompanied by an increase in the local vortex density fluctuations. Through a detailed calculation of correlation functions and critical exponents and by comparison with random field theories, we find that the weak 1D correlations inhibit the effect of random disorder and enhance the stability range of the ordered phase in a 2D vortex lattice.
Work supported by Spanish MINECO, CIG Marie Curie grant, Axa Research Fund and FBBVA.
 I. Guillamon et al., Nature Physics 10, 851?856 (2014)(host Nacho Pascual, nanoGUNE)