Electron-electron scattering is usually dominating the transport in strongly correlated materials. It typically leads to pronounced resistivity maxima in the incoherent regime around the coherence temperature T * , reflecting the tendency of carriers to undergo Mott localization following the demise of the Fermi liquid. This behavior is best pronounced in the vicinity of interaction-driven (Mott-like) metal-insulator transitions, where the T * decreases, while the resistivity maximum ρmax increases. Here we show that, in this regime, the entire family of resistivity curves display a characteristic scaling behavior ρ(T )/ρmax ≈ F (T /Tmax), while the ρmax and Tmax ∼ T * assume a powerlaw dependence on the quasi-particle effective mass m * . Remarkably, precisely such trends are found from an appropriate scaling analysis of experimental data obtained from diluted two-dimensional electron gases in zero magnetic fields. Our analysis provides strong evidence that inelastic electronelectron scattering -and not disorder effects -dominates finite temperature transport in these systems, validating the Wigner-Mott picture of the two-dimensional metal-insulator transition.

We present results from light scattering experiments on tetragonal FeS with the focus placed on lattice dynamics. We identify the Raman active A1g and B1g phonon modes, a second order scattering process involving two acoustic phonons, and contributions from potentially defect-induced scattering. The temperature dependence between 300 and 20 K of all observed phonon energies is governed by the lattice contraction. Below 20 K the phonon energies increase by 0.5-1 cm −1 thus indicating putative short range magnetic order. Along with the experiments we performed latticedynamical simulations and a symmetry analysis for the phonons and potential overtones and find good agreement with the experiments. In particular, we argue that the two-phonon excitation observed in a gap between the optical branches becomes observable due to significant electronphonon interaction.

We report the first principle calculations of the lattice dynamics of KNi2Se2 together with the Raman scattering study. We have observed three out of four Raman active modes predicted by the factor group analysis. Calculated phonon frequencies are in good agreement with experimental findings. Contrary to its iron counterpart (KxFe2−ySe2), K0.95Ni1.86Se2 does not show vacancy ordering.