Role of Electron-Lattice Interaction in Layered Transition Metal Dichalcogenide 2H-NbS_2. I. Phonon Anomaly and Superconductivity

概要

論文の詳細を見る
Lattice dynamics of 2H-NbX_2 (X=S, Se) is studied by taking account of electron-lattice interaction derived microscopically on the basis of the realistic tight-binding bands fitted to the first-principles bands of 2H-NbX_2. Remarkable frequency renormalization of Σ_1 phonon mode around q=(2/3)ΓM is caused due to the characteristic wavevector and mode dependences of the electron-lattice interaction as well as the effect of Fermi surface nesting. It is shown that the short range force constant for neighboring X ions on different X-layers in the same X-Nb-X sandwich determines primarily whether lattice instability occurs (NbSe_2 case) or not (NbS_2 case). By using the electron-lattice interaction and the renormalized phonon frequencies obtained for 2H-NbS_2, the spectral function α^2F(ω) is calculated and the superconducting transition temperature T_c is evaluated by solving the linearized Eliashberg equation. Renormalization of phonon frequencies due to the electron-lattice interaction raises T_c considerably and the obtained value of T_c agrees in order of magnitude with the experimental data. Effects of intercalation on T_c are also discussed.
社団法人日本物理学会の論文
1994-01-15