It was recently discovered that supercurrents flowing through thin superconducting nanowires can be quenched by applying a gate voltage to a nearby gate electrode. This gate control of supercurrents, known as the GCS effect, could enable superconducting transistor logic. Here, we report that the GCS also manifests in a suppression of Meissner screening, establishing the phenomenon as a genuine feature of superconductivity that is not restricted to transport. Using a scanning nitrogen-vacancy (NV) magnetometer at sub-Kelvin temperatures, we image the nanoscale spatial region of GCS suppression in micron-size niobium islands. Our observations are compatible with a microscopic hot-spot model of quasiparticle generation and diffusion, and in conflict with other candidate mechanisms such as Joule heating or an electric field effect. Our work introduces an alternative means for studying quasiparticle dynamics in superconducting nanostructures, and showcases the power of local imaging techniques for understanding emergent condensed matter phenomena.
It was recently discovered that supercurrents flowing through thin superconducting nanowires can be quenched by applying a gate voltage to a nearby gate electrode. This gate control of supercurrents, known as the GCS effect, could enable superconducting transistor logic. Here, we report that the GCS also manifests in a suppression of Meissner screening, establishing the phenomenon as a genuine feature of superconductivity that is not restricted to transport. Using a scanning nitrogen-vacancy (NV) magnetometer at sub-Kelvin temperatures, we image the nanoscale spatial region of GCS suppression in micron-size niobium islands. Our observations are compatible with a microscopic hot-spot model of quasiparticle generation and diffusion, and in conflict with other candidate mechanisms such as Joule heating or an electric field effect. Our work introduces an alternative means for studying quasiparticle dynamics in superconducting nanostructures, and showcases the power of local imaging techniques for understanding emergent condensed matter phenomena.
It was recently discovered that supercurrents flowing through thin superconducting nanowires can be quenched by a gate voltage. This gate control of supercurrents, known as the GCS effect, could enable superconducting transistor logic. Here, we report that the GCS also manifests in a suppression of Meissner screening, establishing the phenomenon as a genuine feature of superconductivity that is not restricted to transport. Using a scanning nitrogen-vacancy magnetometer at sub-Kelvin temperatures, we image the nanoscale spatial region of GCS suppression in micron-size niobium islands. Our observations are compatible with a microscopic hot-spot model of quasiparticle generation and diffusion, and in conflict with other candidate mechanisms such as Joule heating or an electric field effect. Our work introduces an alternative means for studying quasiparticle dynamics in superconducting nanostructures, and showcases the power of local imaging techniques for understanding emergent condensed matter phenomena.
Superconductor nanodevices are widely applied in quantum computers and quantum detectors. Gate-controlled supercurrent (GCS) provides a potential platform for developing quantum systems, but the mechanism remains controversial. Recent reports suggest that there may be out-of-equilibrium phonons acting in GCS, but insightful investigations are lacking. Here, we report an incoherent superconducting nanowire phonon detector to convert the phase transitions induced by out-of-equilibrium phonons into electric pulse signals, enabling discrete-time measurements. The statistical properties of the gate-induced signals reveal the Poisson properties of phonon injection and the thermalization dynamics of hot electrons in the GCS on the α-Si substrate. These mechanisms are further evidenced by applying opposite gate voltages on two remote gates, in which only phonons play a role. The proposed detector not only is a candidate for constructing phonon-based solid quantum devices based on the GCS but also contributes to research on the out-of-equilibrium phenomena in superconducting nanodevices.
The interplay of alternative materials, large-scale integration technologies, and innovative devices plays a pivotal role on the way to fault-tolerant quantum computing. In this context, gate-controlled superconductivity (GCS) emerges as a key enabling technology, promising to advance superconducting logic and quantum electronics, complementing conventional approaches based on Josephson effects and quantum interference. Here, we demonstrate all-metallic superconducting ZrN nanostructures on silicon, fabricated entirely using a subtractive, monolithic dry-etch approach with a 300 mm CMOS-compatible process flow. For Dayem-bridge weak links with decreasing width down to 27 nm, we observe Tc of 7.3 K, width-dependent switching characteristics, and a progressive approach of the tunneling limit. In laterally gated Dayem-bridge and nanowire devices, we observe GCS with full suppression of the critical current, where required gate voltages <5 V promise compatibility with CMOS interfaces. Asymmetries in polarity-dependent power injection via field emission support GCS models that attribute the effect to quasiparticle relaxation through phonon emission. Additional asymmetries in the GCS effect suggest an influence of the substrate condition after dry etching. Field emission features in the gated nanowire device imply superimposed current paths along the gate edge and corners. Finally, we analyze magnetic interference in Dayem-bridge weak links and superconducting quantum interference devices, where quantum interference is governed by Josephson effects and inductance loop asymmetries. Our results contribute to the scaling efforts in hybrid superconducting electronics and quantum-processing units.
The observation of the gate-controlled supercurrent (GCS) effect in superconducting nanostructures initiated major research efforts toward the realisation of superconducting-based computing architectures. Here we introduce a universal logic circuit that can be a promising superconducting building block of classical hybrid supercomputers. We demonstrate a functionally complete set of logic gates by realising the AND, OR, NOT and COPY gates. The general layout and scalability of our device, combined with recent experiments demonstrating fast switching and small voltage signals, make it a functional candidate in superconducting electronics. Our device enables the realization of all classical logic gates and the half-adder combinational logic circuit using at most three nanowires, each uniquely configured with two side-gate electrodes.
High Resolution Image Download MS PowerPoint Slide Logic circuits consist of devices that can be controlled between two distinct states. The recent demonstration that a superconducting current flowing in a constriction can be controlled via a gate voltage ( V G )─gate-controlled supercurrent (GCS)─can lead to superconducting logic with better performance than existing logics. However, before such logic is developed, high reproducibility in the functioning of GCS devices and optimization of their performance must be achieved. Here, we report an investigation of gated Nb devices showing GCS with very high reproducibility. Based on the investigation of a statistically significant number of devices, we demonstrate that the GCS is independent of the constriction width, in contrast with previous reports, and confirm a strong correlation between the GCS and the leakage current ( I leak ) induced by V G . We also achieve a voltage output in our devices larger than the typical values reported to date by at least 1 order of magnitude, which is relevant for the future interconnection of devices, and show that I leak can be used as a tool to modulate the operational V G of devices on a SiO 2 substrates. These results altogether represent an important step forward toward the optimization of reproducibility and performance of GCS devices, and the future development of a GCS-based logic.
Josephson junctions enable dissipation-less electrical current through metals and insulators below a critical current. Despite being central to quantum technology based on superconducting quantum bits and fundamental research into self-conjugate quasiparticles, the spatial distribution of super current flow at the junction and its predicted evolution with current bias and external magnetic field remain experimentally elusive. Revealing the hidden current flow, featureless in electrical resistance, helps understanding unconventional phenomena such as the nonreciprocal critical current, i.e., Josephson diode effect. Here we introduce a platform to visualize super current flow at the nanoscale. Utilizing a scanning magnetometer based on nitrogen vacancy centers in diamond, we uncover competing ground states electrically switchable within the zero-resistance regime. The competition results from the superconducting phase re-configuration induced by the Josephson current and kinetic inductance of thin-film superconductors. We further identify a new mechanism for the Josephson diode effect involving the Josephson current-induced phase. The nanoscale super current flow emerges as a new experimental observable for elucidating unconventional superconductivity, and optimizing quantum computation and energy-efficient devices. Diract imaging of supercurrent flow at a Josephson junction has been inaccessible in experiment. Here, using nanoscale magnetometry, the authors find large kinetic inductance of thin film superconductors can lead to competing Josephson vortex states hidden below the critical current, and also provide a new route towards the Josephson diode effect.