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Register a new userElementary Andreev Processes in a Driven Superconductor-Normal Metal Contact
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We investigate the full counting statistics of a voltage-driven normal metal(N)-superconductor(S) contact. In the low-bias regime below the superconducting gap, the NS contact can be mapped onto a purely normal contact, albeit with doubled voltage and counting fields. Hence in this regime the transport characteristics can be obtained by the corresponding substitution of the normal metal results. The elementary processes are single Andreev transfers and electron- and hole-like Andreev transfers. Considering Lorentzian voltage pulses we find an optimal quantization for half-integer Levitons.
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We report the study of ballistic transport in normal metal/graphene/superconductor junctions in edge-contact geometry. While in the normal state, we have observed Fabry-P{e}rot resonances suggesting that charge carriers travel ballistically, the superconducting state shows that the Andreev reflection at the graphene/superconductor interface is affected by these interferences. Our experimental results in the superconducting state have been analyzed and explained with a modified Octavio-Tinkham-Blonder-Klapwijk model taking into account the magnetic pair-breaking effects and the two different interface transparencies, textit{i.e.},between the normal metal and graphene, and between graphene and the superconductor. We show that the transparency of the normal metal/graphene interface strongly varies with doping at large scale, while it undergoes weaker changes at the graphene/superconductor interface. When a cavity is formed by the charge transfer occurring in the vicinity of the contacts, we see that the transmission probabilities follow the normal state conductance highlighting the interplay between the Andreev processes and the electronic interferometer.
The point contact spectrum between a normal metal and a superconductor often shows unexpected sharp dips in the conductance at voltage values larger than the superconducting energy gap. These dips are not predicted in the Blonder-Tinkham-Klapwizk (BTK) theory, commonly used to analyse these contacts. We present here a systematic study of these dips in a variety of contacts between different combinations of a superconductor and a normal metal. From the correlation between the characteristics of these dips with the contact area, we can surmise that such dips are caused by the contact not being in the ballistic limit. An analysis of the possible errors introduced while analysing such a spectrum with the standard BTK model is also presented.
We present measurements of current noise and cross-correlations in three-terminal Superconductor-Normal metal-Superconductor (S-N-S) nanostructures that are potential solid-state entanglers thanks to Andreev reflections at the N-S interfaces. The noise correlation measurements spanned from the regime where electron-electron interactions are relevant to the regime of Incoherent Multiple Andreev Reflection (IMAR). In the latter regime, negative cross-correlations are observed in samples with closely-spaced junctions.
We report on a new type of Fano effect, named as Andreev-Fano effect, in a hybrid normal-metal / superconductor (N/S) interferometer embedded with a quantum dot. Compared with the conventional Fano effect, Andreev-Fano effect has some new features related to the characteristics of Andreev reflection. In the linear response regime, the line shape is the square of the conventional Fano shape; while in the nonlinear transport, a sharp resonant structure is superposed on an expanded interference pattern, qualitatively different from the conventional Fano effect. The phase dependence of the hybrid N/S interferometer is also distinguished from those of all-N or all-S interferometers.
Crossed Andreev reflection (cAR) is a scattering process that happens in a quantum transport set-up consisting of two normal metals (NM) attached to a superconductor (SC), where an electron incident from one NM results in a hole emerging in the other. Typically, an electron tunnelling through the superconductor from one NM to the other (ET) competes with cAR and masks the signature of cAR in the conductance spectrum. We propose a novel scheme to enhance cAR, in which SC part of the NM-SC-NM is side-coupled to another SC having a different SC phase to form a Josephson junction in the transverse direction. At strong enough coupling and adequate phase difference, one can smoothly traverse between highly ET-dominant to highly cAR-dominant transport regimes by tuning chemical potential, due to the appearance of subgap Andreev states that are extended in the longitudinal direction. We also discuss connections to realistic systems.
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