ANOMALOUS NERNST EFFECT IN THE MIXED-STATE OF THE 2-BAND ORGANIC SUPERCONDUCTORS KAPPA-(BEDT-TTF)(2)CU[N(CN)(2)]BR AND KAPPA-(BEDT-TTF)(2)CU(NCS)(2)

The transverse thermomagnetic Nernst effect in the mixed state of the organic superconducting salts of the kappa-(BEDT-TTF)(2)X family, wher e BEDT-TTF is bis(ethylenedithio) tetrathiafulvalene and X=Cu[N(CN)(2) ]Br and Cu(NCS)(2), has been studied as regards temperature under a ma gnetic field for different in-plane crystal directions, A large anisot ropy of the in-plane Nernst voltage in the conducting plane with a sig n change has been observed and is discussed considering the flux motio n from the viewpoint of the entropy and Magnus forces. The experimenta l results can be explained taking into account the anisotropic two-ban d nature of the conducting system in these compounds and assuming a pr edominant role of the electron-like band in the superconducting pairin g. The peculiarities of the inter-plane Nernst effect in the kappa-(BE DT-TTF)(2)Cu(NCS)(2) salt confirms the proposed interpretation. In thi s case the Nernst voltage is related to the thermal diffusion of the J osephson vortices.