Conduction properties of the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} based on Hubbard{endash}unrestricted-Hartree-Fock band calculations

1997 
The organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} (with T{sub c}=10.4K) possesses a number of puzzling electronic properties, including the temperature dependence of resistivity, magnetic susceptibility, and Hall coefficient. To provide a basis for understanding these properties, we carried out band calculations using the two-dimensional Hubbard model with the unrestricted-Hartree-Fock theory. The electron transfer hopping interactions are from {ital ab initio} calculations. For a Hubbard parameter of U{sub Coul}{approximately}0.6775eV, the calculated results give good agreement with Shubnikov-de Haas and magnetic breakdown experiments. The calculations lead to a two-band semimetal with a momentum gap separating the electron and hole bands. The anomalous experimental observations are explained in terms of BEDT-TTF related phonons coupling these two bands. These results also provide a framework for describing the conduction properties of similar BEDT-TTF crystals. This approach should also be useful for other organic conductors. {copyright} {ital 1997} {ital The American Physical Society}
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