No abstract

Under standard conditions, the electrostatic field-effect is negligible in conventional metals and was expected to be completely ineffective also in superconducting metals. This common belief was recently put under question by a family of experiments that displayed full gate-voltage-induced suppression of critical current in superconducting all-metallic gated nanotransistors. To date, the microscopic origin of this phenomenon is under debate, and trivial explanations based on heating effects given by the negligible electron leakage from the gates should be excluded. Here, we demonstrate the control of the supercurrent in fully suspended superconducting nanobridges. Our advanced nanofabrication methods allow us to build suspended superconducting Ti-based supercurrent transistors which show ambipolar and monotonic full suppression of the critical current for gate voltages of V G C ≃ 18 V and for temperatures up to ∼80% of the critical temperature. The suspended device architecture minimizes the electron−phonon interaction between the superconducting nanobridge and the substrate, and therefore, it rules out any possible contribution stemming from charge injection into the insulating substrate. Besides, our finite element method simulations of vacuum electron tunneling from the gate to the bridge and thermal considerations rule out the cold-electron field emission as a possible driving mechanism for the observed phenomenology. Our findings promise a better understanding of the field effect in superconducting metals.

The control and measurement of local non-equilibrium configurations is of utmost importance in applications on energy harvesting, thermoelectrics and heat management in nano-electronics. This challenging task can be achieved with the help of various local probes, prominent examples including superconducting or quantum dot based tunnel junctions, classical and quantum resistors, and Raman thermography. Beyond time-averaged properties, valuable information can also be gained from spontaneous fluctuations of current (noise). From these perspective, however, a fundamental constraint is set by current conservation, which makes noise a characteristic of the whole conductor, rather than some part of it. Here we demonstrate how to remove this obstacle and pick up a local noise temperature of a current biased diffusive conductor with the help of a miniature noise probe. This approach is virtually noninvasive for the electronic energy distributions and extends primary local measurements towards strongly non-equilibrium regimes.

Semiconductor nanowires featuring strong spin-orbit interactions (SOI), represent a promising platform for a broad range of novel technologies, such as spintronic applications or topological quantum computation. However, experimental studies into the nature and the orientation of the SOI vector in these wires remain limited despite being of upmost importance. Typical devices feature the nanowires placed on top of a substrate which modifies the SOI vector and spoils the intrinsic symmetries of the system. In this work, we report experimental results on suspended InAs nanowires, in which the wire symmetries are fully preserved and clearly visible in transport measurements. Using a vectorial magnet, the non-trivial evolution of weak anti-localization (WAL) is tracked through all 3D space, and both the spin-orbit length l SO and coherence length l ϕ are determined as a function of the magnetic field magnitude and direction. Studying the angular maps of the WAL signal, we demonstrate that the average SOI within the nanowire is isotropic and that our findings are consistent with a semiclassical quasi-1D model of WAL adapted to include the geometrical constraints of the nanostructure. Moreover, by acting on properly designed side gates, we apply an external electric field introducing an additional vectorial Rashba spin-orbit component whose strength can be controlled by external means. These results give important hints on the intrinsic nature of suspended nanowire and can be interesting for the field of spintronics as well as for the manipulation of Majorana bound states in devices based on hybrid semiconductors.Keywords spin-orbit interaction, nanowire, indium arsenide, weak anti-localization, Rashba effect Over the past decades there has been a growing interest in the study of the spin-orbit interactions in semiconductor systems motivated by the possibility of spintronics applications and quantum computing. 1-5 Systems with strong SOI offer an ideal platform to develop cir-arXiv:1807.04344v2 [cond-mat.mes-hall]