Indications of effects of phonon-roton states on electronic transport

In this paper we report strong indications of the effects of phonon-roton states on electronic transport. Under conditions where the wavevector Qp of these states is close to 2kF, inelastic umklapp-scattering effects of the conduction electrons with phonon-roton states can occur. Below a characteristic temperature T0, under which the electronic energy is too low to excite these states, the inelastic umklapp scattering disappears, leaving the elastic umklapp scattering on the static structure and the inelastic scattering on long-wavelength phonons (Debye phonons). The variation in the scattering behaviour with temperature causes pronounced transport anomalies. The thermopower, for example, exhibits a kink at T0 and large deviations from the free-electron behaviour above T0. This effect is responsible for the different sign of the thermopower to the Hall coefficient at elevated temperatures, a long-standing problem which often exists in liquid and amorphous metals. Whereas indications of the inelastic umklapp scattering are also visible in the resistivity, seen as an inflection point where the resistivity which was increasing starts to decrease, the Hall effect seems to be unaffected.