Transverse and in-plane modification of superconductivity and electronic structure in the quasi-two-dimensional organie conductor K-(BEDT-TTF)₂CU(SCN)₂ by uniaxial stress

Abstract

We have employed uniaxial stress along the principal axes of the quasi-two-dimensional organie superconductor κ-(BEDT-TTF)₂CU(SCN)₂ (BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene). The lattice anisotropy is thereby altered, with corresponding changes in the intermolecular transfer energies. The effect of uniaxial stress on the superconducting transition temperature T_c and critical field B_c2 is found to be anisotropic. There is an indication of an inerease in T_c and an inerease in B_c2 for in-plane stress, but both parameters decrease rapidly for transverse (interplane) stress. Magnetotransport studies reveal stress-induced changes in the Fermi surface through the observation of the Shubnikov-de Haas oscillations. The stress dependence of a resistive anomaly in the magnetoresistance, which is associated with the critical field B_c2 , is also investigated. We discuss the experimental findings in the context of recent phenomenological and theoretical treatments of quasi-two-dimensional systems where the anisotropic triangular-lattice Hubbard model has been used to treat two-dimensional superconductors.