An interpretation of the strain-sensitive resistance in κ-(BEDT-TTF)₂Cu(NCS)₂

Recently Kang and co-workers (see ibid., vol.2, p.1665, 1990) reported that the electrical resistance of an organic superconductor kappa -(BEDT-TTF) ₂Cu(NCS)₂ noticeably decreases as a function of hydrostatic pressure; especially up to 1 kbar at 77.4 K where the resistance rapidly decreases by a factor of almost 10. These strain-sensitive resistance behaviours are consistently explained by the extended Hubbard model for a quarter-filling: an inter-site Coulomb repulsion is assumed to open an energy gap (300-500 K at room temperature) at the Fermi level and delicately interplay with the strain-sensitive transfer integrals of quasi-two-dimensional itinerant pi -electrons.