ANISOTROPY EFFECTS ON SUPERCONDUCTIVITY IN LAYERED MATERIAL NBS2

Anisotropy effects of the gap function on superconducting properties i n a 2H-type transition-metal dichalcogenide NbS2 are studied by solvin g the anisotropic Eliashberg equation with the use of Fermi-surface ha rmonics. Due to the characteristic dependences on wave vectors of the electron-phonon interaction and renormalized phonon frequencies, aniso tropic components of the electron-phonon spectral function have relati vely large values in the frequency range between 5 and 10 meV, where t he frequencies of the Sigma(1)-phonon modes around q = 2/3 Gamma M are renormalized significantly. The superconducting transition temperatur e T-c evaluated by solving the anisotropic Eliashberg equation is slig htly higher than that evaluated by solving the isotropic Eliashberg eq uation. Anisotropy of the mass enhancement factor and that of the supe rconducting gap function just below T-c are also evaluated.