oral: "Correlated quenched disorder in vortex matter: the role of twin boundaries in BaFeCoAs pnictides superconductors"

M. MARZIALI BERMÚDEZ; G. PASQUINI; S. L. BUD´KO; P. C. CANFIELD

Buenos Aires

Workshop; LAW3M 2013; 2013

Magnetic and transport properties in type II superconductors are mainly determined by the underlying vortex physics. The vortex-vortex interaction in competition with quenched disorder and thermal fluctuations give raise to a variety of phases, mainly determined by the strength and topology of quenched disorder. In this context, correlated disorder due to linear or planar defects is particularly relevant: Beside the practical advantage to provide the best way to pin vortices and increase critical currents, the underlying physics is very rich: correlated defects can modify the solid phase in a Bosse Glass phase, with a preferential magnetic field direction for which the transition temperature to the liquid phase increases. Moreover, in materials where competition between pinning and elastic forces gives rise to history effects, competition disappears when correlated pinning prevails. Correlated linear disorder can be artificially obtained by heavy-ion irradiation that produces columnar defects (CDs). On the other hand, twin boundaries (TBs), present in materials with orthorhombic structure, are natural source of planar correlated disorder. The correlated nature of pinning produced by TBs and CDs and their efficiency has been extensively probed in high Tc cuprates. The interest in TBs has been renovated with the discovery of the iron-arsenide family Ba(Fe1-xCox)₂As₂, where a structural transition from a tetragonal to orthorhombic lattice, correlated with a magnetic transition, occurs at a temperature Ts(x) that approaches the critical temperature Tc(x) at x∼0.07. In this work we study the angular dependence of the AC susceptibility response in single crystals with slightly different Co content, in the crossover region from tetragonal-untwined to orthorhombic-twinned structures. We observe that a subtle difference in the Co doping produces a dramatic change in the angular dependence. Results are compared with previous work done in the prototypical cuprate YBCO, and the physical implications are discussed.