Current and shot noise in a spin dependent driven normal metal – BCS superconductor junction
arxiv(2023)
摘要
Andreev reflection is a fundamental transport process occurring at the
junction between a normal metal and a superconductor (a N-S junction), when an
incident electron from the normal side can only be transmitted in the
superconductor as a Cooper pair, with the reflection of a hole in the normal
metal. As a consequence of the spin singlet nature of the BCS Cooper pairs, the
current due to Andreev reflection at a N-S junction is always symmetric in
spin. Using a Keldysh Nambu Floquet approach, combining analytical and
numerical calculations, we study in details the AC transport at a N-S junction,
when the two spin components in the normal metal are driven by different
periodic drives. We show that, in the Andreev regime, i.e. when the
superconducting gap is much larger than the frequency of the drives, the
spin-resolved photo-assisted currents are always equal even if the two drives
are different. In addition, we show that in this regime the excess noise
depends only on the sum of the periodic drives, and we consider in particular
the case of Lorentzian pulses (Levitons). We also show how these properties get
modified when going beyond the Andreev regime. Finally we give a simple
analytical proof of the special properties of the Andreev regime using an exact
mapping to a particular N-N junction.
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