Superconducting spin filter

N. M. Chtchelkatchev

L. D. Landau Institute for Theoretical Physics RAS, 117940 Moscow, Russia

Institute for High Pressure Physics, Russian Academy of Sciences

142092 Troitsk, Moscow Region, Russia

PACS: 74.50.+r, 74.80.Fp, 75.75.+a

**Abstract**

Consider two normal leads coupled to a superconductor;
the first lead is biased while the second one and the
superconductor are grounded. In general, a finite current
I_{2}(V_{1},0) is induced in the grounded lead 2; its magnitude
depends on the competition between processes of Andreev and normal
quasiparticle transmission from the lead 1 to the lead 2. It is
known that in the tunneling limit, when normal leads are weakly
coupled to the superconductor, I_{2}(V_{1},0)=0, if |V_{1}|<Δ
and the system is in the clean limit. In other words, Andreev and
normal tunneling processes compensate each-other. We consider the
general case: the voltages are below the gap, the system is either
dirty or clean. It is shown that I_{2}(V_{1},0)=0 for general
configuration of the normal leads; if the first lead injects spin
polarized current then I_{2}=0, but spin current in the lead-2 is
finite. XISIN structure, where X is a source of the spin polarized
current could be applied as a filter separating spin current from
charge current. We do an analytical progress calculating
I_{1}(V_{1},V_{2}), I_{2}(V_{1},V_{2}).