J. S. Parker

Superconducting quantum phase transitions tuned by magnetic impurity and magnetic field in ultrathin a-Pb films

Superconducting quantum phase transitions tuned by disorder (d), paramagnetic impurity (MI) and perpendicular magnetic field (B) have been studied in homogeneously disordered ultrathin a-Pb films. The MI-tuned transition is characterized by progressive suppression of the critical temperature to zero and a continuous transition to a weakly insulating normal state with increasing MI density. In all important aspects, the d-tuned transition closely resembles the MI-tuned transition and both appear to be fermionic in nature. The B-tuned transition is qualitatively different and probably bosonic. In the critical region it exhibits transport behavior that suggests a B-induced mesoscale phase separation and presence of Cooper pairing in the insulating state.

Controlling the magneto-transport properties of EuS thin films

The growth of thin films of the ferromagnetic semiconductor EuS on [100] oriented GaAs substrates by electron-beam evaporation is demonstrated. Structural characterization by X-ray diffraction reveals [100] oriented growth. In general, the magnetic and transport properties can strongly be influenced by the deposition parameters. We systematically investigate the influence of the growth temperature T/sub S/ in the range T/sub S/=235 K-675 K on the above properties. The Curie temperature increases with decreasing growth temperature, while the magnetic transition becomes broader. The resistivity decreases over four orders of magnitude with decreasing substrate temperature. The behavior of the magnetic properties and the resistivity can be explained by a change in stoichiometry, leading to higher carrier concentrations for lower substrate temperatures. Hall-effect measurements, magnetoresistance, and temperature dependence of the resistivity show a qualitative behavior known from bulk EuS samples. The demonstrated tunability of the magnetic and transport properties opens a wide range of possible applications for EuS in spin-electronics.

Measurement of the spin polarization of the magnetic semiconductor EuS with zero-field and Zeeman-split Andreev reflection spectroscopy

We report measurements of the spin polarization

Spin polarization of CrO2 at and across an artificial barrier.

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Direct measurement of the spin polarization of the magnetic semiconductor (Ga,Mn)As.

of the concentrated magnetic semiconductor

Large inverse magnetoresistance of CrO2/Co junctions with an artificial barrier

\mathrm{EuS}

Braden et al. Reply

using both zero-field and Zeeman-split Andreev reflection spectroscopy (ARS) with

The effect of 3

\mathrm{EuS}∕\mathrm{Al}

d

planar junctions. The zero-field ARS spectra are well described by the modified (spin-polarized) Blonder-Tinkham-Klapwijk (BTK) model with expected superconducting energy gap and actual measurement temperature (no additional spectral broadening). The fittings consistently yield

paramagnetic impurities on superconductivity in quench-condensed amorphous Pb films

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