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Nonlocal quasiparticle transport in normal-superconductor-normal (NSN) hybrid structures probes sub-gap states in the proximity region and is especially attractive in the context of Majorana research. Conductance measurement provides only partial information about nonlocal response composed from both electron-like and hole-like quasiparticle excitations. In this work, we show how a nonlocal shot noise measurement delivers a missing puzzle piece in NSN InAs nanowire-based devices. We demonstrate that in a trivial superconducting phase quasiparticle response is practically charge-neutral, dominated by the heat transport component with a thermal conductance being on the order of conductance quantum. This is qualitatively explained by numerous Andreev reflections of a diffusing quasiparticle, that makes its charge completely uncertain. Consistently, strong fluctuations and sign reversal are observed in the sub-gap nonlocal conductance, including occasional Andreev rectification signals. Our results prove conductance and noise as complementary measurements to characterize quasiparticle transport in superconducting proximity devices.

We present an innovative strategy to control a thermal bias in nanoscale electronic conductors which is based on the contact heating scheme. This straightforward approach allows one to apply a known thermal bias across nanostructures directly through metallic leads, avoiding conventional substrate intermediation. We show, by using the average noise thermometry and local noise sensing technique in InAs nanowire-based devices, , that a nanoscale metallic constriction on a SiO 2 substrate acts like a diffusive conductor with negligible electron-phonon relaxation and non-ideal leads. The non-universal impact of the leads on the achieved thermal bias -which depends on their dimensions, shape and material composition -can be quantified via a proper design of the nanodevice. Our results are relevant for accurate thermoelectric or similar 1 arXiv:1812.06463v1 [cond-mat.mes-hall] 16 Dec 2018 measurements at nanoscale, allowing to reduce the issue of the thermal bias calibration to the knowledge of the heater resistance.Recently, this approach was successfully applied to TE measurements in individual InAs

We investigate the proximity effect in InAs nanowire (NW) junctions with superconducting contacts made of Al. The carrier density in InAs is tuned by means of the back gate voltage Vg. At high positive Vg the devices feature transport signatures characteristic of diffusive junctions with highly transparent interfaces -sizable excess current, re-entrant resistance effect and proximity gap values (∆N ) close to the Al gap (∆0). At decreasing Vg, we observe a reduction of the proximity gap down to ∆N ≈ ∆0/2 at NW conductances ∼ 2e 2 /h, which is interpreted in terms of carrier density dependent reduction of the Al/InAs interface transparency. We demonstrate that the experimental behavior of ∆N is closely reproduced by a model with shallow potential barrier at the Al/InAs interface.A possibility to interface a superconductor (S) with a metallic (N) state of InAs-based mesoscopic semiconductors is known since at least two decades 1,2 . High critical and excess currents, sometimes comparable to a theoretical upper limit, are reliably observed in InAs nanowire (NW) Josephson junctions 3-5 . Observations of signatures of a Cooper pair splitting 6,7 further conform with high device quality. A recent revival of interest in proximity effect in S-NW devices emerged in the course of a search for Majorana zero-energy states 8 , with the research targeted at single conduction channel NWs 9-12 .Thanks to a well-known Fermi level pinning effect, which results in a charge accumulation at the surface of InAs 13,14 , the NWs grown from this material typically exhibit low contact resistance to normal metals. For the superconducting hybrid devices, however, even a weak interface reflectivity can sufficiently degrade the performance by suppressing the Andreev reflection in favor of the normal quasiparticle scattering 15,16 . Although the transparency of the S/NW interfaces can be controlled by various chemical treatments prior to the deposition of the superconductor 3-5,17 or, alternatively, via the in-situ MBE growth of the superconductor 18 , residual imperfections are still present 19,20 . One might expect that the underlying physics can be clarified by tracking the carrier density dependence of the proximity effect, since the effective interface transparency should critically depend on the shape of the potential barrier.In this work we study the evolution of the superconducting proximity effect in an InAs NW with evaporated Al contacts as a function of electron density in InAs, which is controlled by means of a global back gate. At high carrier densities, the transport data is compatible with highly transparent Al/InAs interfaces and the induced proximity gap (∆ N ) is close to the superconducting gap value in Al (∆ 0 ). The observed reduction of ∆ N by a factor of two at decreasing carrier density indicates gate-tunable interface transparency, which can be explained assuming a shallow potential barrier formed at the Al/InAs interface.We investigate unintentionally doped catalyst free InAs NWs grown by MBE on a Si(111) substrate. ...