Theoretical Study of Lattice Instability and Lattice Dynamics of 2H-TaSe₂ and 2H-NbSe₂. I. Electron-Lattice Interaction and Generalized Electronic Susceptibility

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Lattice instability of 2H-TaSe₂ and 2H-NbSe₂ is studied on the basis of the electronic band structure of these compounds obtained by a tight-binding fit to Mattheiss’ band calculation. The wave number and mode dependences of the electron-lattice coupling matrix and the generalized electronic susceptibility are calculated. The results are discussed in connection with the lattice instability.