Small-angle neutron scattering reveals dynamic reorganization and metastable configurations in vortex matter

MARZIALI BERMÚDEZ, MARIANO*; LOUDEN, ELIZABETH R.; ESKILDSEN, MORTEN R.; BEKERIS, VICTORIA; PASQUINI, GABRIELA

Ciudad Autónoma de Buenos Aires

Congreso; 1er Congreso Argentino de Técnicas Neutrónicas; 2017

In type-II superconductors, the magnetic field penetrates in quantized flux lines called vortices. Whereas intervortex interactions promote an ordered vortex lattice (VL), both thermal fluctuations and pinning interactions tend to disorder the system. This makes vortex matter an excellent model system for the experimental study of general properties a broad class of complex systems. In weak pinning materials, such as NbSe2 single crystals, competing interactions result in a rich phase diagram featuring an order-disorder transition (ODT). Although the stable ordered Bragg glass (BG) and the disordered phase have been widely studied, thermal and dynamic history effects in the VL near the ODT remained controversial and poorly understood for decades. Here we present recently published illuminating results[1,2] from a series of combined small angle neutron scattering (SANS) and linear ac-susceptibility experiments in clean NbSe2 single crystals. Based on SANS data, we identified different degrees of disorder in the VL after various controlled thermal and dynamic protocols. In addition, in-situ susceptibility data offered the possibility to explore the connection between order and vortex mobility (i.e., effective pinning). Our results strongly support the existence of a transitional region between the ordered and disordered phases. In this region, dynamically-originated configurations show intermediate degrees of disorder, correlated with intermediate pinning responses. On the other hand, thermal cycling of the system through the ODT led to metastable superheated and supercooled VL configurations that coexist with hysteretic effective pinning. Our observations and proposed scenario may shed light on the long-standing debate regarding the origin of the studied history effects.[1] M. Marziali Berm ́udez, M. R. Eskildsen, M. Bartkowiak, G. Nagy, V. Bekeris, and G. Pasquini. Phys. Rev. Lett. 115, 067001 (2015).[2] M. Marziali Berm ́udez, E. R. Louden, M. R. Eskildsen, C. D. Dewhurst, V. Bekeris, and G. Pasquini. Phys. Rev. B. (2017). In press. arXiv:1701.08798 [cond-mat.supr-con].*: expositor. Formato: póster