Dehybridization transition in intermetallic transition-metal compounds

The classical s-d theory of Mott for transition metals is reconsidered. The s and d states hybridize at low temperatures, and the electron-phonon coupling constant λ of the hybridized state is dominated by the d component. As the temperature rises, the electron-phonon scattering rage of the d states, τ_dd^-1, exceeds the hybridization integral J_sd (more precisely, [Equation Found], and as a result the s and d components of the wavefunction become dehybridized, forming decoupled s and d channels, as in the original Mott theory. This process is described using a simple Drude-like theory, which turns out to be somewhat analogous to motional narrowing in NMR and EPR. In specific transition-metal intermetallic compounds, the value of the hybridization integral J_sd, derived from the electronic band structure, is small (10-50meV), and as a result the dehybridization takes place at rather low temperatures (100-200K), accounting for anomalies in the resistivity observed there experimentally. At higher temperatures the scattering rate of the s electrons is given by [Equation Found] where λ_s is the electron-phonon coupling of the s channel, and tdd saturates a value h/ΔE_d, the inverse of the d bandwidth. This model applies to intermetallic compounds possessing the A-15 structure, to valence-fluctuation compounds, possibly to materials considered in the past to be spin-fluctuation compounds, to Chevrel phases, and in general to many intermetallic compounds with transition-metal elements.