A detailed analysis is given of the T 2 term in the resistivity observed in electron-doped SrTiO3. Novel bandstructure data are presented, which provide values for the bare mass, density of states, and plasma frequency of the quasiparticles as a function of doping. It is shown that these values are renormalized by approximately a factor 2 due to electron-phonon interaction. It is argued that the quasiparticles are in the anti-adiabatic limit with respect to electron-phonon interaction. The condition of anti-adiabatic coupling renders the interaction mediated through phonons effectively non-retarded. We apply Fermi-liquid theory developed in the 70's for the T 2 term in the resistivity of common metals, and combine this with expressions for Tc and with the Brinkman-Platzman-Rice (BPR) sum-rule to obtain Landau parameters of n-type SrTiO3. These parameters are comparable to those of liquid 3 He, indicating interesting parallels between these Fermi-liquids despite the differences between the composite fermions from which they are formed. PACS numbers:arXiv:1109.3050v1 [cond-mat.str-el]

We report a comprehensive THz, infrared and optical study of Nb doped SrTiO3 as well as DC conductivity and Hall effect measurements. Our THz spectra at 7 K show the presence of a very narrow (< 2 meV) Drude peak, the spectral weight of which shows approximately a factor of three enhancement of the band mass for all carrier concentrations. The missing spectral weight is regained in a broad 'mid-infrared' band which originates from electron-phonon coupling. We find no evidence of a particularly large electron-phonon coupling that would result in small polaron formation. Analysis of the results yields an electron-phonon coupling parameter of an intermediate strength, α ≈ 4.PACS numbers: 71.38.-k, 72.20.-i, 78.20.-e Electron-phonon coupling in the perovskites is a subject of much recent interest due to the controversy over its relevance in the phenomena of multiferroicity, ferroelectricity, superconductivity and colossal magnetoresistance [1,2,3,4,5]. Despite much progress, full understanding of the physics of electron-phonon coupling in perovskites is still lacking because of additional crystallographic complexities of many materials involved (breathing, tilting and rotational distortions, ferroelectric symmetry breaking), magnetism, complex electronic effects (strong correlations), and also because of the lack of high-accuracy spectroscopic measurements specifically designed to probe electron-phonon coupling.With this in mind, we have studied a prototypical perovskite oxide, SrTi 1−x Nb x O 3 with 0 ≤ x ≤ 0.02. SrTiO 3 is an insulator (∆ = 3.25 eV) with the conduction band formed by the Ti 3d states. These are split by the crystal field so that the three t 2g states become occupied when the material is electron-doped by substituting pentavalent Nb for tetravalent Ti. For 0.0005 ≤ x ≤ 0.02 SrTi 1−x Nb x O 3 becomes superconducting at a T c of typically ∼ 0.3 K [6,7], and at most 1.2 K [5]. Characterized by the threefold degeneracy of the conduction bands and the high lattice polarizability, electron doped SrTiO 3 provides a perfect opportunity for the study of electronphonon coupling and polaron formation in an archetypal perovskite [8,9].

Recent experimental data on the optical conductivity of niobium doped SrTiO3 are interpreted in terms of a gas of large polarons with effective coupling constant α ef f ≈ 2. The theoretical approach takes into account many-body effects, the electron-phonon interaction with multiple LOphonon branches, and the degeneracy and the anisotropy of the Ti t2g conduction band. Based on the Fröhlich interaction, the many-body large-polaron theory provides an interpretation for the essential characteristics, except -interestingly -for the unexpectedly large intensity of a peak at ∼ 130 meV, of the observed optical conductivity spectra of SrTi1−xNbxO3 without any adjustment of material parameters.

We present measurements of Zeeman-level population lifetimes in Er 3+ :Y 2 SiO 5 at low magnetic fields and low temperatures. Using spectral hole burning spectroscopy, we investigate the dynamics and temperature dependence of the hole structure due to the Zeeman interaction. Evidence for population storage in Zeeman levels with lifetimes of up to 130 ms is found in the form of long-lived spectral holes and antiholes. We also observe that a subset of the erbium ions exhibit very long-lived holes with lifetimes as long as 60 s at 2.8 K.

The structural, thermodynamic and optical properties of Mg 2 Ni thin films covered with Pd are investigated upon exposure to hydrogen. Similar to bulk, thin films of metallic Mg 2 Ni take up 4 hydrogen per formula unit and semiconducting transparent Mg 2 NiH 4−␦ is formed. The dielectric function ⑀ of Mg 2 Ni and fully loaded Mg 2 NiH 4−␦ is determined from reflection and transmission measurements using a Drude-Lorentz parametrization. Besides the two "normal" optical states of a switchable mirror-metallic reflecting and semiconducting transparent-Mg 2 NiH x exhibit a third "black" state at intermediate hydrogen concentrations with low reflection and essentially zero transmission. This state originates from a subtle interplay of the optical properties of the constituent materials and a self-organized double layering of the film during loading. Mg 2 NiH 4−␦ preferentially nucleates at the film/substrate interface and not-as intuitively expected-close to the catalytic Pd capping layer. Using ⑀ Mg 2 Ni and ⑀ Mg 2 NiH 4 and this loading sequence, the optical response at all hydrogen concentrations can be described quantitatively. The uncommon hydrogen loading sequence is confirmed by x-ray diffraction and hydrogen profiling using the resonant nuclear reaction 1 H͑ 15 N,␣␥͒ 12 C. Pressure-composition isotherms suggest that the formation of Mg 2 NiH 4−␦ at the film/substrate interface is mainly due to locally enhanced kinetics.