New superconducting phases in field-induced organic superconductor λ-(BETS) 2FeCl4 -: art. no. 227001

We derive the parallel upper critical field, H-c2, as a function of the temperature T in quasi-2D organic compound lambda-(BETS) 2FeCl4, accounting for the formation of the nonuniform Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state. To further check the 2D LOFF model, we propose to study the H-c2(T) curve at low T in tilted fields, where the vortex state is described by the high Landau level functions characterized by the index n. We predict a cascade of first-order transitions between vortex phases with different n, between phases with different types of the symmetry at given n and the change of the superconducting transition from the second order to the first order as FeCl4 ions are replaced partly by GaCl4 ions.