Daniel Springer

Polaronic transport and magnetism in Ag-doped ZnO

Magnetic polarons have been proposed to play important roles in doped wide band gap oxides that exhibit weak room temperature ferromagnetism. Here, we report the experimental evidence supporting polaronic magnetism and transport in Ag-doped ZnO. Temperature dependent resistivity data suggest the conduction mechanism of Mott and Efros variable range hopping. The observed weak ferromagnetism and its temperature dependence are explained using the percolation-based model of partially ordered bound magnetic polarons.

Temperature-dependent terahertz conductivity of tin oxide nanowire films

Temperature-dependent terahertz conductivity of tin oxide (SnO2) nanowire films was measured from 10 to 300K using terahertz time-domain spectroscopy. The optical parameters, including the complex refractive index, optical conductivity and dielectric function, were obtained using a simple effective medium theory. The complex conductivity was fitted with the Drude-Smith model and the plasmon model. The results show that the carrier density (N) and plasmon resonance frequency (ω0) increase while the scattering time decreases with increasing temperature. The reduced carrier mobility compared with bulk SnO2 indicates the presence of carrier localization or trapping in these nanowires. (Some figures may appear in colour only in the online journal)

Effect of annealing on the temperature-dependent dielectric properties of LaAlO3 at terahertz frequencies

We present THz conductivity of LaAlO3 (LAO) as a function of temperature and annealing, using terahertz time-domain spectroscopy(THz-TDS). We observed that, after annealing, spectral weight redistribution occurs, such that the real conductivity σ1(ω) changed from a featureless and almost frequency-independent spectrum, into one where peaks occur near the phonon frequencies. These phonon frequencies increase with increasing temperature. We attribute the appearance of these absorption peaks to the diffusion and relocation of oxygen vacancies. The dielectric functions of annealed LAO are well fitted with the Drude-Lorentz model.

Doping dependence of the electron–phonon and electron–spin fluctuation interactions in the high-Tc superconductor Bi2Sr2CaCu2O8+δ

Using ultrafast optical techniques, we detect two types of bosons strongly coupled to electrons in the family of Bi2Sr2CaCu2O8+? (Bi-2212) from the underdoped to overdoped regimes. The different doping dependences of the electron?boson coupling strengths enable us to identify them as phonons and spin fluctuations: electron?phonon coupling (?e?ph) peaks at optimal doping, while electron?spin fluctuation coupling (?e?sf) decreases monotonically with doping. This observation is consistent with two facts: (i) superconductivity is in close proximity with antiferromagnetism at low dopings and (ii) a pronounced lattice renormalization effect at larger dopings.

Ultrafast relaxation dynamics in BiFeO3/YBa2Cu3O7 bilayers

The temperature dependence of the relaxation dynamics in the bilayer thin film heterostructure composed of multiferroic BiFeO

Interfacial effects revealed by ultrafast relaxation dynamics in BiFeO

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(BFO) and superconducting YBa

/YBa

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Cu

Cu

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