ANOMALOUS BEHAVIOR OF THE THERMOELECTRIC-POWER IN THE VICINITY OF THESUPERCONDUCTING TRANSITION IN THE ORGANIC SUPERCONDUCTORS KAPPA-(BEDT-TTF)(2)CU(NCS)(2) AND KAPPA-(BEDT-TTF)(2)CU[N(CN)(2)]BR

The in-plane thermoelectric power (TEP) of the layered organic superco nductors kappa-(BEDT-TTF)(2)Cu(NCS)(2) and kappa-(BEDT-TTF)(2)Cu[N(CN) (2)]Br has been studied in the vicinity of the superconducting transit ion under magnetic held. Below the transition temperature, an anomalou s non-monotonic behavior of the TEP is found in the kappa-(BEDT-TTF)(2 )Cu(NCS)(2) salt; instead of a gradual monotonic decrease, the TEP sho ws a prominent sign-change before vanishing. Similar, although less pr onounced features have been found in the other compound. The change in sign of the TEP is explained in terms of the two-fluid counterflow mo del, assuming a predominant role of one of the two anisotropic bands ( namely, the electron-like one) in the superconducting pairing.