Decomposing the Bragg glass and the peak effect in a Type-II superconductor

Abstract

Adding impurities or defects destroys crystalline order. Occasionally, however, extraordinary behaviour emerges that cannot be explained by perturbing the ordered state. One example is the Kondo effect, where magnetic impurities in metals drastically alter the temperature dependence of resistivity. In Type-II superconductors, disorder generally works to pin vortices, giving zero resistivity below a critical current jc. However, peaks have been observed in the temperature and field dependences of jc. This peak effect is difficult to explain in terms of an ordered Abrikosov vortex lattice. Here we test the widespread paradigm that an order-disorder transition of the vortex ensemble drives the peak effect. Using neutron scattering to probe the vortex order in superconducting vanadium, we uncover an order-disorder transition from a quasi-long-range-ordered phase to a vortex glass. The peak effect, however, is found to lie at higher fields and temperatures, in a region where thermal fluctuations of individual vortices become significant.

Universal behavior of the intermediate mixed state domain formation in superconducting niobium

“…For FC measurements, the microscopic magnetic flux redistribution is shown, starting from the normal state (1) with a homogeneous distribution, to the regular VL in the SH (2). In the IMS (3,4) the VL breaks up into domains containing an increasingly dense VL.…”

“…pronounced pinning, indicating a breakdown of pinning at the onset of the vortex attraction.Conventional superconductors are divided by the Ginzburg-Landau parameter κ into type-I (κ < 1/ √ 2) and type-II (κ > 1/ √ 2), which, additionally to the Meissner state (MS) exhibit the Shubnikov state (SS). In the SS, magnetic vortices form a variety of vortex matter (VM), such as the Abrikosov vortex lattice (VL) [1], glassy [2][3][4] or liquid [5][6][7] states. Type-II superconductors are further subdivided, where type-II/2 (κ 1/ √ 2) features a purely repulsive inter-vortex interaction.…”

Anomalous peak effect in iron-based superconductors Ba1−xKxFe2As2 ( Terashima1, Kikugawa2, Kiswandhi3 et al. 2019Phys. Rev. B6030View full textAdd to dashboardCite

“…We, however, note the following: those previous works were based on the observation of a single peak of J c in the peak effect region and associated it with the boundary between the disordered solid and liquid phases. A very recent small angle neutron scattering study on vanadium, however, claims that the peak effect lies at higher fields and temperatures than the order-disorder transition [22].…”

Unveiling the vortex glass phase in the surface and volume of a type-II superconductor

“…Interestingly, the saturation value η ∼ 0.025 that we found at the surface of the vortex structure nucleated in the Bragg glass phase is roughly one order of magnitude smaller than the value found in the same phase from bulk SANS measurements in single-crystalline vanadium. 23 This indicates that vortex meandering within the sample thickness is significant even though the orientational order of the Bragg glass is long-ranged in the whole sample volume.…”