Crossed Andreev effects in two-dimensional quantum Hall systems

We study the crossed Andreev effects in two-dimensional conductor/superconductor hybrid systems under a perpendicular magnetic field. Both a graphene/superconductor hybrid system and an electron gas/superconductor one are considered. It is shown that an exclusive crossed Andreev reflection, with other Andreev reflections being completely suppressed, is obtained in a high magnetic field because of the chiral edge states in the quantum Hall regime. Importantly, the exclusive crossed Andreev reflection not only holds for a wide range of system parameters, e.g., the size of system, the width of central superconductor, and the quality of coupling between the graphene and the superconductor, but also is very robust against disorder. When the applied bias is within the superconductor gap, a robust Cooper-pair splitting process with high-efficiency can be realized in this system.Comment: 10 pages, 10 figure

Possible alterations of the gravitational field in a superconductor

In this paper I calculate the possible alteration of the gravitational field in a superconductor by using the time-dependent Ginzburg-Landau equations (TDGL). I compare the behaviour of a high-Tc superconductor (HTCS) like YBa_2Cu_3O_7 (YBCO) with a classical low-Tc superconductor (LTCS) like Pb. Finally, I discuss what values of the parameters characterizing a superconductor can enhance the reduction of gravitational field.Comment: LaTex2e, 10 pages, 3 figure

Conductance of a junction between a normal metal and a Berezinskii superconductor

The conductance of a junction between a normal metal and a superconductor having the symmetry proposed by Berezinskii is studied theoretically. The main feature of this symmetry is the odd frequency dependence of the anomalous Green function, which makes possible the s-wave triplet superconducting state (the Berezinskii superconductor). The Andreev reflection (which links positive and negative energies) is sensitive to the energetic symmetry; as a result, the conductance of the junction involving the Berezinskii superconductor is qualitatively different from the case of a conventional superconductor. Experimentally, the obtained results can be employed to test the possibility of the Berezinskii superconductivity proposed for Na$_x$CoO$_2$ and to identify the odd-omega component predicted for superconductor-ferromagnet junctions.Comment: 5 pages (including 3 EPS figures

Domain wall effects in ferromagnet-superconductor structures

We investigate how domain structure of the ferromagnet in superconductor-ferromagnet heterostructures may change their transport properties. We calculate the distribution of current in the superconductor induced by magnetic field of Bloch domain walls, find the ``lower critical'' magnetization of the ferromagnet that provides vortices in the superconductor