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Resumen del trabajo presentado a la Conference Low dimensional superconducting hybrids for novel quantum functionalities, celebrada en Paris (Francia) del 12 al 14 de octubre de 2021.

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 ?-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.

We report on the realization of Nb-based all-metallic Dayem nano-bridge gate-controlled transistors (Nb-GCTs). These Josephson devices operate up to a temperature of ~ 3 K and exhibit full suppression of the supercurrent thanks to the application of a control gate voltage. The dependence of the kinetic inductance and of the transconductance on gate voltage promises a performance already on par with so far realized metallic Josephson transistors and leads us to foresee the implementation of a superconducting digital logic based on the Nb-GCT. We conclude by showing the practical realization of a scheme implementing an all-metallic gate-tunable half-wave rectifier to be used for either superconducting electronics or photon detection applications.

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La Juglans regia (L.) è una specie arborea multi-funzionale, nota per il legno pregiato e i frutti di qualità, che cresce in Italia da 0 a 1500 m s.l.m.. Nelle aree montane e marginali ha svolto a lungo un ruolo importante per la sussistenza della famiglia rurale e per la connotazione paesaggistica e idrogeologica del territorio. In tali aree ancor'oggi esistono molte varietà locali e/o ecotipi, scarsamente conosciuti o negletti, degni di essere riscoperti e valorizzati. Il progetto FIMONT, finanziato dal MiUR, tra i cinque case studies affrontati, ha considerato il "Noce di Montagna" per suggerire informazioni, metodi e strategie che possano incrementare il valore del germoplasma montano di noce. A tal fine si è proceduto a: 1) l'individuazione di una macroarea di studio rappresentativa dei territori montani d'Italia vocati alla nocicoltura; 2) l'analisi dello stato dell'arte delle dinamiche di filiera, delle noci e della frutta secca, all'interno della macroarea di studio; 3) la messa a punto di metodologie per il controllo di provenienza del Noce di Montagna (marcatori molecolari); 4) lo sviluppo di strategie per la valorizzazione del prodotto. L'analisi degli aspetti di filiera ha evidenziato diversi punti critici. Sul mercato tradizionale le produzioni non specializzate di Noci di Montagna non sono economicamente e tecnologicamente competitive nei confronti di produzioni specializzate e internazionali. Le analisi genetiche, però, hanno evidenziato delle particolarità che sembrano collegare le popolazioni di noce, campionate nelle aree appenniniche interne, all'antichissima pratica della transumanza delle greggi. Ulteriori analisi su gruppi di noci campionati lungo il percorso del Regio Tratturo Pescasseroli-Candela sembrano rafforzare l'ipotesi. Gli spostamenti operati dall'uomo nel corso dei secoli hanno influenzato la naturale dinamica di diffusione del noce e hanno determinato, insieme ai fattori ambientali, la selezione di ecotipi genetici particolari che si distinguono nettamente dalle varietà più diffuse nel sud Italia. La ricerca ha così legato il Noce di Montagna al Regio Tratturo e alla transumanza, fornendo una caratteristica fortemente utile a connotare il prodotto Noce di Montagna. Il caso studio Noce di Montagna è un interessante esempio di come metodologie analitiche di laboratorio di tipo genetico e molecolare possano rappresentare uno strumento utile per il controllo e la caratterizzazione del prodotto. I metodi e le strategie seguite possono essere applicati con successo in altre realtà.

Recent experiments have shown the possibility of tuning the transport properties of metallic nanosized superconductors through a gate voltage. These results renewed the longstanding debate on the interaction between electrostatic fields and superconductivity. Indeed, different works suggested competing mechanisms as the cause of the effect: an unconventional electric field-effect or quasiparticle injection. Here, we provide conclusive evidence for the electrostatic-field-driven control of the supercurrent in metallic nanosized superconductors, by realizing ionic-gated superconducting field-effect nanotransistors (ISFETs) where electron injection is impossible. Our Nb ISFETs show giant suppression of the superconducting critical current of up to similar to 45%. Moreover, the bipolar supercurrent suppression observed in different ISFETs, together with invariant critical temperature and normal-state resistance, also excludes conventional charge accumulation/depletion. Therefore, the microscopic explanation of this effect calls upon a novel theory able to describe the nontrivial interaction of static electric fields with conventional superconductivity.

We demonstrate the first \textit{all-metallic} mesoscopic superconductor-normal metal-superconductor (SNS) field-effect controlled Josephson transistors (SNS-FETs) and show their full characterization from the critical temperature $T_c$ down to 50 mK in the presence of both electric and magnetic field. The ability of a static electric field -applied by mean of a lateral gate electrode- to suppress the critical current $I_s$ in a proximity-induced superconductor is proven for both positive and negative gate voltage values. $I_s$ suppression reached typically about one third of its initial value, saturating at high gate voltages. The transconductance of our SNS-FETs obtains values as high as 100 nA/V at 100 mK. On the fundamental physics side, our results suggest that the mechanism at the basis of the observed phenomenon is quite general and does not rely on the existence of a true pairing potential, but rather the presence of superconducting correlations is enough for the effect to occur. On the technological side, our findings widen the family of materials available for the implementation of all-metallic field-effect transistors to \textit{synthetic} proximity-induced superconductors., 11 pages, 5 color figures

Gate-tunable Josephson junctions (JJs) are the backbone of superconducting classical and quantum computation. Typically, these systems exploit low charge concentration materials, and present technological diffculties limiting their scalability. Surprisingly, electric field modulation of supercurrent in metallic wires and JJs has been recently demonstrated. Here, we report the realization of titanium-based monolithic interferometers which allow tuning both JJs independently via voltage bias applied to capacitively-coupled electrodes. Our experiments demonstrate full control of the amplitude of the switching current (IS) and of the superconducting phase across the single JJ in a wide range of temperatures. Astoundingly, by gate-biasing a single junction the maximum achievable total IS suppresses down to values much lower than the critical current of a single JJ. A theoretical model including gate-induced phase fluctuations on a single junction accounts for our experimental findings. This class of quantum interferometers could represent a breakthrough for several applications such as digital electronics, quantum computing, sensitive magnetometry and single-photon detection., Comment: 9 pages, 4 figures

Superconducting field-effect transitor (SuFET) and Josephson field-effect transistor (JoFET) technologies take advantage of electric field induced control of charge carrier concentration in order to modulate the channel superconducting properties. Despite field-effect is believed to be unaffective for superconducting metals, recent experiments showed electric field dependent modulation of the critical current (IC) in a fully metallic transistor. Yet, the grounding mechanism of this phenomenon is not completely understood. Here, we show the experimental realization of Ti-based Dayem bridge field-effect transistors (DB-FETs) able to control IC of the superconducting channel. Our easy fabrication process DB-FETs show symmetric full suppression of IC for an applied critical gate voltage as low as VCG~+-8V at temperatures reaching about the 85% of the record critical temperature TC~550mK for titanium. The gate-independent TC and normal state resistance (RN) coupled with the increase of resistance in the supercoducting state (RS) for gate voltages close to the critical value (VCG) suggest the creation of field-effect induced metallic puddles in the superconducting sea. Our devices show extremely high values of transconductance (gMAXm~15uA/V at VG~+-6.5V) and variations of Josephson kinetic inductance (LK) with VG of two orders of magnitude. Therefore, the DB-FET appears as an ideal candidate for the realization of superconducting electronics, superconducting qubits, tunable interferometers as well as photon detectors., 9 pages, 4 figures

In the last 60 years conventional solid and electrolyte gating allowed sizable modulations of the surface carrier concentration in metallic superconductors resulting in tuning their conductivity and changing their critical temperature. Recent conventional gating experiments on superconducting metal nano-structures showed full suppression of the critical current without variations of the normal state resistance and the critical temperature. These results still miss a microscopic explanation. In this article, we show a complete set of gating experiments on Ti-based superconducting Dayem bridges and a suggested classical thermodynamic model which seems to account for several of our experimental findings. In particular, zero-bias resistance and critical current IC measurements highlight the following: the suppression of IC with both polarities of gate voltage, the surface nature of the effect, the critical temperature independence from the electric field and the gate-induced growth of a sub-gap dissipative component. In addition, the temperature dependence of the Josephson critical current seems to show the transition from the ballistic Kulik-Omelyanchuck behavior to the Ambegaokar-Baratoff tunnel-like characteristic by increasing the electric field. Furthermore, the IC suppression persists in the presence of sizeable perpendicular-to-plane magnetic fields. We propose a classical thermodynamic model able to describe some of the experimental observations of the present and previous works. Above all, the model grabs the bipolar electric field induced suppression of IC and the emergence of a sub-gap dissipative component near full suppression of the supercurrent. Finally, applications employing the discussed effect are proposed., Comment: 13 pages, 7 figures

International audience; Heterostructured InAs/InSb nanowire (Nw) based field effect transistors (FET) have been fabricated and tested as Terahetz radiation detectors. While responsivity and noise equivalent power compare with the ones of InAs nanowire detectors, the presence of small-gap InSb semiconductor gives rise to interesting physical effects such an increase of the detected signal with charge injection through the wire, at odds with standard FET-detectors. Additionally, the photodetected signal voltage changes its sign after a threshold gate bias, which we explain considering surface-related transport and field asymmetries imposed by the use of a lateral gate electrode.

By exploiting the resonant coupling between a travelling wave and the stationary modes of a cavity, we present the first scheme for integrated automatic interaction-free surface acoustic wave routing of fluids. Our scheme opens the way to the implementation of logic gates based on instantaneous liquid distribution.

We present a planar laser diode based on a simple fabrication scheme compatible with virtually any geometry accessible by standard semiconductor lithography technique. We show that our lasers exhibit similar to 1 GHz -3 dB-modulation-bandwidth already in this prototypical implementation. Directions for a significant speed increase are discussed. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3672438]

We report the magnetotransport properties of a two-dimensional electron gas in a modulation-doped AlGaAs/GaAs heterostructure subjected to a lateral potential with honeycomb geometry. Periodic oscillations of the magnetoresistance and a delocalized-localized transition are shown by applying a gate voltage. We argue that electrons in such artificial-graphene lattices offer a promising approach for the simulation of quantum phases dictated by Coulomb interactions. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3493189]

We demonstrate anti-bunched emission from a lateral-light emitting diode. Sub-Poissonian emission statistic, with a g(2)(0) = 0.7, is achieved at cryogenic temperature in the pulsed low-current regime, by exploiting electron injection through shallow impurities located in the diode depletion region. Thanks to its simple fabrication scheme and to its modulation bandwidth in the gigahertz range, we believe our devices are an appealing substitute for highly attenuated lasers in existing quantum-key-distribution systems. Our devices outperform strongly attenuated lasers in terms of multi-photon emission events and can therefore lead to a significant security improvement in existing quantum key distribution systems.