Colloquium

Type-IV Superconductivity and Dimensional Crossovers in a Magnetic Field

A.G. Lebed   
University of Arizona
Landau Institute for Theoretical Physics
Wednesday, April 26, 2006
Higgins 310, 4 pm

Type-IV superconductivity, defined as a d(s)-wave singlet superconductor in zero magnetic field or the Meissner phase which demonstrates a singlet-triplet mixed order parameter in the vortex phase. This phenomenon is shown to be general and based on careful account of spin-splitting paramagnetic effects and related symmetry properties of superconducting order parameters, and therefore does not depend on the microscopic mechanism of superconductivity. It is shown that singlet-triplet mixing effects are expected to be of the order of unity in such modern superconductors as high-T_c, organic, and MgB₂ materials.
In addition, a unified theory of magnetic phenomena in low-dimensional organic conductors and superconductors is suggested, based on the notion of dimensional crossovers for some many-body and one-body effects. This theory explains such unique experimentally-observed phenomena as field-induced spin- and charge-density-waves and related 3D QHE, superconductivity surviving at ultra-high magnetic fields, H » H_c2, and magic angle effects in magnetoresistance.