L. P. Gor'kov

Methods of quantum field theory in statistical physics

Abrikosov, Gorkov, Dzyaloshinski, Methods of quantum field theory in statistical physics Fetter, Walecka, Quantum theory of many-particle systems T. Schaefer, Quark Matter, hep-ph/0304281. J. Kogut, M. Stephanov, The Phases of QCD, Cambridge University Press (2004). K. Rajagopal, F. Wilczek, The Condensed Matter Physics of QCD, hep-ph/0011333. J. Lattimer and M. Prakash, The Physics of Neutron Stars, astro-ph/0405262. D. Kaplan, Five lectures on effective field theory, nucl-th/0510023.

Superconducting 2D System with Lifted Spin Degeneracy: Mixed Singlet-Triplet State

Motivated by recent experimental findings, we have developed a theory of the superconducting state for 2D metals without inversion symmetry modeling the geometry of a surface superconducting layer in a field-effect transistor or near the boundary doped by adsorbed ions. In such systems the twofold spin degeneracy is lifted by spin-orbit interaction, and singlet and triplet pairings are mixed in the wave function of the Cooper pairs. As a result, spin magnetic susceptibility becomes anisotropic and Knight shift retains finite and rather high value at T = 0.

Superconductivity in an Organic Insulator at Very High Magnetic Fields

We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor lambda-(BETS)2FeCl4. Below 4 K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41 T and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field compensates the exchange field of aligned Fe3+ ions. We further argue that the Fe3+ moments are essential to stabilize the resulting singlet, two-dimensional superconducting state.

On the theory of the structural properties of A-15 type materials

The theory of the structural properties of the A-15 compounds is developed starting with a picture of linear chains of atoms of the transition elements. The twofold-degenerate electronic term is shifted and split when interchain transfer is taken into account. A fine structure of the electronic spectrum and the density of states are examined. The latter has two singularities at the Fermi level corresponding to an estimated variation of the composition by several percent. Among the samples showing the martensitic transformation, one of these singularities is supposed to be responsible for the peculiar properties observed, and a theory of the transformation from the cubic to the tetragonal phase is suggested. The temperature dependence of the phonon spectrum has been studied in detail. The theory explains the softening of the phonon modes at large wave vectors in some directions, and predicts features of the phonon spectrum whose observation could be crucial to the theory.

Inhomogeneous stripe phase revisited for surface superconductivity.

We consider 2D surface superconductivity in high magnetic fields parallel to the surface. We demonstrate that the spin-orbit interaction at the surface changes the properties of the inhomogeneous superconducting Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state that develops above fields given by the paramagnetic criterion. Strong spin-orbit interaction significantly broadens the range of existence of the LOFF phase, which takes the form of periodic superconducting stripes running along the field direction on the surface, leading to the anisotropy of its properties. Our results provide a tool for studying surface superconductivity as a function of doping.

Singlet magnetism in heavy fermions.

We consider singlet magnetism for the uranium ions in UPt

Ferromagnetism and superstructure in Ca1-xLaxB6

_3

IDENTIFICATION OF THE SUPERCONDUCTIVITY TYPE IN ORGANIC SUPERCONDUCTORS.

and URu

Peculiarities in low temperature properties of doped manganites A1-xBxMnO3

_2

Singularities in the density of electronic states of one-dimensional conductors with disorder

Si