Gate Control of the Current–Flux Relation of a Josephson Quantum Interferometer Based on Proximitized Metallic Nanojuntions

Abstract

We demonstrate an Al superconducting quantum interference device in which the Josephson junctions are implemented through gate-controlled proximity Cu mesoscopic weak links. This specific kind of metallic weak links behaves analogously to genuine superconducting metals in terms of the response to electrostatic gating and provides a good performance in terms of current-modulation visibility. We show that through the application of a static gate voltage we can modify the interferometer current−flux relation in a fashion that seems compatible with the introduction of π-channels within the gated weak link. Our results suggest that the microscopic mechanism at the origin of the suppression of the switching current in the interferometer is apparently phase coherent, resulting in an overall damping of the superconducting phase rigidity. We finally tackle the performance of the interferometer in terms of responsivity to magnetic flux variations in the dissipative regime and discuss the practical relevance of gated proximity-based all-metallic SQUIDs for magnetometry at the nanoscale.

Ultra-Highly Linear Magnetic Flux-to-Voltage response in Proximity-based Mesoscopic bi-SQUIDs

“…Finally, f t M decays with the temperature from the value of 10 mV/φ 0 obtained at 30 mK, and vanishes for T 500 mK. On this point we emphasize that, in terms of the transfer function, our SNS bi-SQUID outperforms by two orders of magnitude interferometers of similar typology 44,47 .…”

“…Finally, through the screening parameter β 1,2 the rings inductances are accounted for 1 . By means of a fit of the I S (B) 44,47 curves against the RSJ model, we extracted the relevant device parameters at 30 mK such as the effective loop areas (∼ 22 ± 0.7 µm 2 and ∼ 2 ± 0.7 µm 2 ), the asymmetry parameters (α = 0.23 ± 0.1 and α 3 = 0.6 ± 0.2), and the screening parameters (β 1 = 2.1 ± 0.7 and β 2 = 0.7 ± 0.7). Such values are in agreement with the design of our SNS bi-SQUID.…”

“…The latter, indeed, can be regulated during the fabrication by properly setting the section and the length of the weak-links, and the relative thickness and the size of the overlapping area of the S and N regions. Furthermore, the critical current of SNS JJs can be tuned down to zero by the application of a gate control voltage 43,44 . This last feature, which was not demonstrated so far for tunnel junctions, might be exploitable to vary and improve the device performances during its operation 45 .…”

“…In this work, we demonstrate the operation of Al bi-SQUIDs in which three nano-junctions are implemented through proximitized mesoscopic Cu weak-links. Although its relatively low critical temperature, Al was chosen due to its efficient proximization capability over copper 43,44 , but we emphasize that this scheme can be easily exploited in a higher temperature working range by simply replacing the Al with higher critical temperature superconductors, such as Nb 46 or V 47,48 . Hence, the fruition of this identical technology to regimes of operation ranging between 4K to 10K is achievable Finally, our devices exhibit a very promising fluxto-voltage response characteristics which, in this prototypical realization, let us to foresee a performance already on pair with that of bi-SQUIDs arrays composed of hundreds of tunnel junction-based interferometers.…”

Frustration driven Josephson phase dynamics

“…A special role in this context is played by the so called πphase shifts and π-pairing, i.e., antiphase relation between order parameters or equivalently the sign reversal of the effective Josephson coupling between Cooper pairs. This is at the heart of unconventional superconductivity, e.g., in cuprates [3,4], iron-based [5,6] and oxide interface superconductors [7,8], superconductor-ferromagnetsuperconductor junctions [9], phase qubits [10], electrically or orbitally driven superconducting phases [11][12][13][14],…”