Observation of a gel of quantum vortices in a superconductor at very low magnetic fields

Abstract

A gel consists of a network of particles or molecules formed for example using the sol-gel process, by which a solution transforms into a porous solid. Particles or molecules in a gel are mainly organized on a scaffold that makes up a porous system. Quantized vortices in type II superconductors mostly form spatially homogeneous ordered or amorphous solids. Here we present high-resolution imaging of the vortex lattice displaying dense vortex clusters separated by sparse or entirely vortex-free regions in β-Bi2Pd superconductor. We find that the intervortex distance diverges upon decreasing the magnetic field and that vortex lattice images follow a multifractal behavior. These properties, characteristic of gels, establish the presence of a novel vortex distribution, distinctly different from the well-studied disordered and glassy phases observed in high-temperature and conventional superconductors. The observed behavior is caused by a scaffold of one-dimensional structural defects with enhanced stress close to the defects. The vortex gel might often occur in type-II superconductors at low magnetic fields. Such vortex distributions should allow to considerably simplify control over vortex positions and manipulation of quantum vortex states. arXiv:1904.10999v2 [cond-mat.supr-con]

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

“…Research on vortex matter nucleated in type-II superconductors has shed light on the structural properties of elastic objects nucleated in media with different types of disorder 21 – 47 . A handful of works study the spatial distribution of particle-particle interaction forces to get information on the vortex-disorder interaction 48 – 54 .…”

“…As in many systems of interacting elastic objects, the structural properties of vortex matter result from the balance between thermal, particle-particle and particle-disorder interaction energies. Many theoretical and experimental studies describe the structural deviations from a perfect hexagonal vortex lattice induced by different pinning landscapes 12 , 21 – 47 , 55 – 59 . Correlation function and structure factor studies have been performed in order to characterize the structure of the different glassy phases stabilized by disorder with different geometrical properties, including randomly-distributed point pins 43 , 45 , 46 and correlated defects 21 , 22 , 53 , as well as periodic distributions of pinning sites 17 .…”

“…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 .…”

Disordered hyperuniformity in superconducting vortex lattices

“…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]. Vortex arrangements are then strongly influenced by their interaction with pinning centers.…”

Superconductivity in a disordered metal with Coulomb interactions

“…a function F (α) which is obtained from τ (Q), α(Q) and the said logarithmic derivative as explained in Refs. [58,60].…”