Hyperuniform vortex patterns at the surface of type-II superconductors

Abstract

A many-particle system must posses long-range interactions in order to be hyperuniform at thermal equilibrium. Hydrodynamic arguments and numerical simulations show, nevertheless, that a three-dimensional elastic-line array with short-ranged repulsive interactions, such as vortex matter in a type-II superconductor, forms at equilibrium a class-II hyperuniform two-dimensional point pattern for any constant-z cross section. In this case, density fluctuations vanish isotropically as ∼ q α at small wave-vectors q, with α = 1. This prediction includes the solid and liquid vortex phases in the ideal clean case, and the liquid in presence of weak uncorrelated disorder. We also show that the three-dimensional Bragg glass phase is marginally hyperuniform, while the Bose glass and the liquid phase with correlated disorder are expected to be non-hyperuniform at equilibrium. Furthermore, we compare these predictions with experimental results on the large-wavelength vortex density fluctuations of magnetically decorated vortex structures nucleated in pristine, electron-irradiated and heavy-ion irradiated superconducting Bi2Sr2CaCu2O 8+δ samples in the mixed state. For most cases we find hyperuniform two-dimensional point patterns at the superconductor surface with an effective exponent α eff ≈ 1. We interpret these results in terms of a large-scale memory of the high-temperature line-liquid phase retained in the glassy dynamics when field-cooling the vortex structures into the solid phase. We also discuss the crossovers expected from the dispersivity of the elastic constants at intermediate length-scales, and the lack of hyperuniformity in the xy plane for lengths q −1 larger than the sample thickness due to finite-size effects in the z-direction. We argue these predictions may be observable and propose further imaging experiments to test them independently.arXiv:1907.00394v1 [cond-mat.dis-nn]

Non-Gaussian tail in the force distribution: a hallmark of correlated disorder in the host media of elastic objects

“…periodic distributions of pinning sites 17 . Recently, some studies focusing on characterizing long 46,60 or shortrange 47 vortex density fluctuations obtained contrasting results for samples with point or correlated disorder, see the discussion in Supplementary Note 1. From the perspective of technological applications, having information on the nature and distribution of disorder in a given sample is crucial since correlated in addition to point-like disorder is more efficient to pin vortices and thus to enhance the material critical current 12 .…”

Jamming, fragility and pinning phenomena in superconducting vortex systems

“…As a result, it may be possible to determine whether elastic, fragile, jammed or pinned behavior is likely to occur by examining the vortex configurations even before a drive is applied. This can be achieved experimentally using a variety of imaging techniques [56][57][58][59] .…”

Disordered hyperuniformity in superconducting vortex lattices

“…In a recent work, vortex lattices at very small magnetic fields were analyzed in view of their hyperuniform properties. Those authors analyzed images of the high-T c cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ with magnetic Bitter decoration in the presence of disorder [23]. At small magnetic fields, vortices are very far apart and their mutual repulsion is small [50,51].…”

“…The authors of Ref. [23] concluded that long-wavelength fluctuations are systematically suppressed in the vortex lattice at small magnetic fields, as a consequence of the hydrodynamic properties of the liquid phase, which leads to deviations from fully random vortex distributions.…”

“…Arrangements of vortices in cuprate superconductors at very small magnetic fields where weak intervortex interactions are weak were discussed in Ref. [23].…”