Charge, spin and lattice degrees of freedom are strongly entangled in iron superconductors. A neat consequence of this entanglement is the behavior of the A_{1g} As-phonon resonance in the different polarization symmetries of Raman spectroscopy when
undergoing the magneto-structural transition. In this work we show that the observed behavior could be a direct consequence of the coupling of the phonons with the electronic excitations in the anisotropic magnetic state. We discuss this scenario within a five orbital tight-binding model coupled to phonons via the dependence of the Slater-Koster parameters on the As position. We identify two qualitatively different channels of the electron-phonon interaction: a geometrical one related to the Fe-As-Fe angle and another one associated with the modification upon As displacement of the Fe-As energy integrals pdsigma and pdpi. While both mechanisms result in a finite B_{1g} response, the behavior of the phonon intensity in the A_{1g} and B_{1g} Raman polarization geometries is qualitatively different when the coupling is driven by the angle or by the energy integral dependence. We discuss our results in view of the experimental reports.
We explore the charge transport mechanism in organic semiconductors based on a model that accounts for the thermal intermolecular disorder at work in pure crystalline compounds, as well as extrinsic sources of disorder that are present in current exp
erimental devices. Starting from the Kubo formula, we develop a theoretical framework that relates the time-dependent quantum dynamics of electrons to the frequency-dependent conductivity. The electron mobility is then calculated through a relaxation time approximation that accounts for quantum localization corrections beyond Boltzmann theory, and allows us to efficiently address the interplay between highly conducting states in the band range and localized states induced by disorder in the band tails. The emergence of a transient localization phenomenon is shown to be a general feature of organic semiconductors, that is compatible with the bandlike temperature dependence of the mobility observed in pure compounds. Carrier trapping by extrinsic disorder causes a crossover to a thermally activated behavior at low temperature, which is progressively suppressed upon increasing the carrier concentration, as is commonly observed in organic field-effect transistors. Our results establish a direct connection between the localization of the electronic states and their conductive properties, formalizing phenomenological considerations that are commonly used in the literature.
It has been recently argued that inverse-beta nuclear transmutations might occur at an impressively high rate in a thin layer at the metallic hydride surface under specific conditions. In this note we present a calculation of the transmutation rate w
hich shows that there is little room for such a remarkable effect.
