Inivited talk; Vortex matter in superconductors: from memory effects to dybnamical reorganziation

VICTORIA I. BEKERIS

San Carlos de Bariloche

Simposio; Slafes XXIII; 2018

Instituto Balseiro

Vortices in low and high Tc superconductors : from memory effects to dynamic reorganization The repulsive interaction between vortex lines in type II superconductors, in addition to the pressure exerted by the applied magnetic field, leads to ordered periodic vortex arrays. However, thermal fluctuations and additional effective forces originated in the vortex interaction with random sample defects compete against order and lead to disordered vortex configurations that may contain topological defects. These are common features in a variety of systems, particularly in colloids, magnetic bubbles, charge and spin waves, but in the case of vortex matter (VM) the relative strength of competing forces may be modified with field or temperature, driving the system across an order-disorder transition signaled by an anomalous sudden increase in disorder and pinning. We have extensively explored this region of the phase diagram both in low and in high Tc superconductors, and I will present the experimental results and numerical simulations of our group describing remarkable memory and history effects [1]. In high Tc superconductors we have found robust metastable configurations sensitive to the symmetry of the oscillatory driving forces applied to reorganize the system [1]. In low Tc samples, we have used sensitive non-invasive techniques to probe the degree of pinning of the different vortex configurations molded by thermal history effects and by controlled driving forces. I will show evidence of a dynamical organization [2] similar to that reported in colloids, where the final state is independent of the initial configuration but is tagged by the oscillatory forcing frequency. The proposed pictures have been very recently supported in our joint linear ac susceptibility and neutron scattering experiments and I will show evidence of strong non trivial correlations between order and VM mobility. [3][1] S.O. Velenzuela and V. Bekeris, Phys.Rev Lett 84 4200 (2000); ibid 86 504 (2001)[2] G. Pasquini et al., Phys. Rev Lett. 100 247003 (2008)[3] M. Marziali Bermúdez et al., Phys Rev Lett 115, 067001, (2015); Phys. Rev. B 95, 104505 (2017).