Speaker
Mr.
Jose Benito Llorens
(Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada UAM, CSIC, Departamento de Física de la Materia Condensada)
Description
The arrangements of cells in a chicken eye are not randomly disordered, but are instead hyperuniform. This allows for a better distribution of elements needed for vision, helping chickens use their vision cells more efficiently. As we show here, hyperuniformity is also observed in superconducting vortex lattices, even when vortex pinning centers are arranged randomly and not hyperuniformly. We discuss consequences of this newly found feature of the vortex lattice.
First, lets us define the term "hyperuniform". A 2D random distribution of particles shows bunching, resulting in spatial fluctuations of the density that increase together with the area. That is, if we consider particles within a circular area with radius r, the density fluctuations increase with rα and α = 2. This also means that the structure factor does not go to zero for small k and the corresponding distribution of particles has been termed "hyperuniform" [1], [2]. Interactions among particles often decrease bunching, resulting in distributions where the density fluctuations increase with α < 2 and the structure factor decreases with kβ and β > 0.
Here we analyze images of disordered superconducting vortex lattices taken with a scanning tunneling microscope. We start by analyzing the potential that creates the disorder influencing the vortex lattice and present two limiting cases, random pinning and uncorrelated long range disorder created by a 1D potential at an angle with the vortex lattice. The latter is a hyperuniform potential in a somewhat trivial way, because it results from a discommensuration between two ordered lattices.
We find that in both cases, the structure factor of the vortex lattice decreases to zero for large wavelengths with power laws ranging between k1 and k2. It has been recently shown that a hyperuniform distribution of pinning centers is favorable to increase the critical current, because it reduces the appearance of channels for vortex transport and allows for a larger occupancy of pinning sites [3]. We discuss imaging experiments showing vortex motion and their relevance for the proposed phenomena.
[1] Salvatore Torquato and Frank H. Stillinger, Phys. Rev. E 68, 069901 (2003).
[2] Atsushi Ikeda, Ludovic Berthier, Giorgio Parisi, arXiv: 1701.00936 (2017).
[3] Q. Le Thien, D. McDermott, C.J. Olson Reichhardt and C. Reichhardt, arXiv: 1611.01532 (2016).
Primary author
Mr.
Jose Benito Llorens
(Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada UAM, CSIC, Departamento de Física de la Materia Condensada)
