RESUMO
Optical spectroscopy was used to study the electrodynamics and hidden transport properties of a BaFe1.91Ni0.09As2thin superconducting (SC) film. We analyzed the normal state data using a Drude-Lorentz model with two Drude components: one narrow (D1) and another broad one (D2). In the SC state, two gaps with2Δ0(2)/kBTc=1.9-2.0 and2Δ0(1)/kBTc=4.0-4.3 are formed from the narrow component D1while the broad component D2remains ungapped. The calculated total DC resistivity of the film and the low-temperature scattering rate for the narrow Drude component show a hidden Fermi-liquid behavior. The change of total electron-boson coupling (λtot) and representative energy (Ω0) in the normal state with respect to the SC state is typical of other iron-based materials as well as high-temperature superconducting (HTSC) cuprates.
RESUMO
Accurate low temperature charge transport measurements in combination with high-precision x-ray diffraction experiments have allowed detection of the symmetry lowering in the single domain Tm0.19Yb0.81B12 crystals that belong to the family of dodecaborides with metal-insulator transition. Based on the fine structure analysis we discover the formation of dynamic charge stripes within the semiconducting matrix of Tm0.19Yb0.81B12. The charge dynamics in these conducting nano-size channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (~2.4 × 1011 Hz) of quantum motion of the charge carriers. It is suggested that cooperative Jahn-Teller effect in the boron sublattice is a cause of the large-amplitude rattling modes of the Tm and Yb ions responsible for the 'modulation' of the conduction band along one of the [Formula: see text] directions through the variation of 5d-2p hybridization of electron states.