New mechanism for the electrical resistivity of layer compounds: TiS2

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Abstract
The authors propose that electrons in the layer compound TiS2 are strongly coupled to a soft interlayer mode. The soft-mode frequency is estimated to be 10-20 cm-1 and is the lowest frequency mode in the system. This mode is not observed by Raman scattering in a monolayer compound because it corresponds to a zero frequency at zero wavevector and must be looked for by neutron scattering. From symmetry, this mode couples only quadratically to the electrons, leading to a resistivity p varies as T2 for T>or=20K in agreement with the observed T2 law for the resistivity of TiS2 for 20K1+xS2 and may account for the observed x dependence of the temperature dependence of rho .