Positive cross correlations of noise in superconducting hybrid structures: Roles of interfaces and interactions

Abstract

Shot noise cross-correlations in normal metal-superconductor-normal metal structures are discussed at arbitrary interface transparencies using both the scattering approach of Blonder, Tinkham and Klapwik and a microscopic Green's function approach. Surprisingly, negative crossed conductance in such set-ups [R. Mélin and D. Feinberg, Phys. Rev. B 70, 174509 (2004)] does not preclude the possibility of positive noise cross-correlations for almost transparent contacts. We conclude with a phenomenological discussion of interactions in the one dimensional leads connected to the superconductor, which induce sign changes in the noise cross-correlations.

High-efficiency Cooper pair splitting demonstrated by two-particle conductance resonance and positive noise cross-correlation

“…Indeed, it had been predicted and measured that Cooper pairs, emanating from a superconductor, can split into two normal metallic leads in the so-called cross Andreev reflection process [4][5][6][7][8][9][10][11] . Such process can be conclusively verified by observing positive coincident arrival events, namely, positive cross-correlation of current fluctuations in two separated normal metallic leads that collect the split pairs [12][13][14][15][16][17][18] . The main difficulty in identifying such process is the overwhelming flux of Cooper pairs that enters the normal leads via direct Andreev reflection (the proximity effect).…”

Noise Correlations in Three-Terminal Diffusive Superconductor–Normal-Metal–Superconductor Nanostructures

“…Whereas negative correlations are expected from a semi-classical approach neglecting proximity effect [14], positive correlations at sub-gap energies are predicted for intermediate values of transparencies [15]. Positive correlations could also arise from synchronized Andreev reflections [16]. In a normal metallic dot connected to all superconducting leads, positive or negative correlations are expected, depending upon properties of contacts between the dot and its leads [17].…”

Noise cross-correlation and Cooper pair splitting efficiency in multi-teminal superconductor junctions

“…4). Finally for hight transparencies T N → 1, the differential nonlocal shot noise is completely positive because for a transparent lead the CAR have additional contributions of intermediate propagators in the superconducting region [32]. In addition, the noise cross-correlation exhibits an exponential decay with respect to the distance between the leads (see Fig.…”

“…Our aim is to obtain the noise cross-correlations and the Fano factor. For s-wave superconductors, the nonlocal shot noise has been calculated [32], showing that, whereas the CAR contribute positively to the crossed correlation between the currents in the two leads [48][49][50], the EC contributes negatively [51]. Local processes like the Andreev reflections (AR) and quasiparticles transmission (Q) contribute negatively to the nonlocal shot noise (see Fig.…”

“…For example, for two electrodes connected to a normal metal, the nonlocal shot noise shows a negative crossed correlation, which indicates that when the electrical current in one lead increases, the current in the other lead decreases [28][29][30]. However the nonlocal shot noise for two leads connected to a superconductor can exhibits positive values [31,32] that is, the electrical current in the two leads could increase or decrease at the same time.…”