Effect of a magnetic field on tunneling conductance in quantum wire/d-wave superconductor junctions

The differential conductance and the effect of a magnetic field on the scattering of the quasiparticles in a quantum wire/d-wave superconductor junction are examined theoretically in this work. When the wire is aligned along the (100) axis of the superconductor, the differential conductance has a peak in the energy gap, the peak is shifted and its height decreases as the magnetic field increases. For orientations (110) of the wire and null magnetic field, the zero bias conductance peak is removed because the Andreev reflections vanish. The effect of applying a magnetic field in the latter case is to recover the Andreev reflections. Additionally two peaks instead of one appear in the differential conductance, one close to zero voltage and the other to a voltage smaller than the energy gap. These peaks are due to the Doppler shift in the spectrum of the quasiparticles and to the diffraction of the wave function quasiparticle in the contact. The most relevant contribution of this study is the conclusion that Andreev reflections can be controlled by mean of a magnetic field. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)