Quantum phase transition in non-uniform superconductors

We consider a phase transition from normal metal into the superconducting state at low temperature in the presence of magnetic field. If the orbital effects are relatively weak and the impurity concentration is low enough, then the quantum critical point (QCP) corresponds to a transition from normal to non-uniform superconducting Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The main directions of our research are:

(a) Superconducting fluctuations of the order parameter in the normal state. The zero-temperature fluctuations near the FFLO state lead to divergent contributions to the spin susceptibility in two-dimensional case, and to a breakdown of Fermi liquid picture at QCP.

(b) Mean-field approach to the properties of the normal state: applications to heavy-fermion materials and especially cold gases in magnetic traps. In gases (⁶Li, ⁴⁰K) orbital and impurity effects are suppressed, thus the formation of a superfluid analog of FFLO state is possible. Anisotropic atomic interaction (for instance, its dipolar component) leads to the formation of a non-uniform mixed-parity superfluid state.

Fluctuations and ultrasound in layered organic superconductors

Transport properties and superconductivity in quasi-2D organic materials. Typical examples of such materials are (BEDT-TTF)₂-X organic compounds. These organic materials can be good conductors or even superconductors under certain conditions. Their structure leads to a strong anisotropy of electronic properties and results in quasi-1D or quasi-2D behavior. The same compound can be an antiferromagnet or a superconductor, it can show a pseudogap behavior, or can be a paramagnetic or Mott insulator at different temperatures and pressures. We study propagation of ultrasound and other transport properties near the superconducting phase transition. The ultrasound technique is able to detect the characteristic anomalies which allow one to construct the material phase diagram, and because they can probe the coupling of the elastic strain to various material states, these studies have important practical applications.

Mesoscopic physics

Tunneling in normal metal - superconductor (NS) contacts, and Josephson junctions. We consider hybrid systems formed by several normal metal electrodes connected to the superconductor. If the distance between the electrodes is small enough, the coherence of two electron states forming the Cooper pair in the superconductor is partially preserved even when the electrons from the same pair tunnel into two different normal electrodes. Systems of this type can be used as a source of entangled electron pairs which have potential applications in quantum cryptography, quantum teleportation and can be good candidate for the basic element of quantum computers.