Koshelev Alexei Superconductivity and Magnetism Group
Materials Science Division
Argonne National Laboratory

Recent Projects

Lattice configurations and magnetic oscillations in stacks of Josephson junctions
A key phenomenon related to the Josephson effect is oscillations of different properties of superconducting tunneling junctions with magnetic field. Magnetic oscillations of critical current in stacks of intrinsic Josephson junctions, which are realized in mesas fabricated from layered high-temperature superconductors, are qualitatively different from oscillations in a single junction. Depending on the stack lateral size, oscillations may have either the period of half flux quantum per junction (wide-stack regime) or one flux quantum per junction (narrow-stack regime). See details
Vortex chain states and phase transitions
In very anisotropic layered superconductors magnetic field tilted at very small angle with respect to the layers generates array of vortex chains. The internal chain structure depends on relation between Josephson and magnetic interlayer couplings and it is relatively simple in two limiting cases: (i)tilted-vortex chain is realized in the case of dominating Josephson coupling (ii) for dominating magnetic coupling the chain is composed of a crossing array of Josephson vortices and pancake-vortex stacks [crossing chain]. The chain phase diagram in the situation when both couplings are of the same order occurs to be surprisingly rich. There are many intermediate chain configurations and several nontrivial phase transformations between different chain structures. See animation (avi, 5.6MB) which shows example of chain-structure evolution with increasing c-axis field.  See details

Josephson vortices and solitons inside pancake vortex lattice in layered superconductors

In very anisotropic layered superconductors tilted magnetic field generates two interpenetrating vortex sublattices. This set of crossing lattices contains a sublattice of Josephson vortices and a sublattice of pancake-vortex stacks. The pancake-vortex sublattice modifies structure of the Josephson vortex in a very unusual way. See details

Theory of multiband superconductors

Collaborator: Alexander Golubov (Univ. of Twente, The Netherlands)
The multigap superconductivity in the recently discovered compound magnesium diboride (MgB2) has been theoretically predicted and confirmed by many experiments. We investigate a simple microscopic model of MgB2, a two-band superconductor with strong intraband and weak interband electronic scattering rates and compute different observable properties within this model including structure of the vortex core and upper critical field for  different orientations. See details
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