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Ad hoc interface printed circuit boards (PCBs) are today the standard connection between cryogenic cabling and quantum chips. Besides low-loss and low-temperature-dependent-dielectric-permittivity materials, Flame Resistance n.4 (FR4) provides a low-cost solution for the fabrication of cryogenic PCBs. Here, we report on an effective way to evaluate the dielectric performance of an FR4 laminate used as a substrate for cryogenic microwave PCBs. We designed a coplanar waveguide $\lambda $ /2 open-circuit series resonator, and we fabricated the PCB using a low-cost manufacturing process, obtaining in-plane geometric features with maximum variations of 50– $100~\mu \text{m}$ compared to the PCB design. Such a geometry allows to exploit the resonance peak of the resonator to measure the variation of the complex permittivity as a function of the temperature. The resonance peak frequency was used to estimate the real permittivity, achieving a sensitivity of −470 MHz and a resolution of $1.2\times 10^{-2}$ . Similarly, the resonance peak magnitude was involved in the extrapolation of the loss tangent, reaching a sensitivity of ~−337 dB and a resolution of $1.6\times 10^{-4}$ . For the FR4 laminate used, we estimated a 9% reduction of the real permittivity and a 70% reduction of the loss tangent in the temperature range from 300 K to 4 K. The proposed approach can be immediately extended to the detection of cryogenic temperature-dependent dielectric performance of any kind of substrate.

A novel superconducting device based on voltage-controlled critical current suppression has been demonstrated, with the capability of being employed as a superconducting three-terminal gate-assisted transistor: the EF-Tron. In this work, we explore the potential of the EF-Tron for building superconducting logic elements. We have developed a continuous Verilog-A model and performed SPICE simulations of different logical circuits, including examples of combinatorial, sequential circuits, and ring oscillator. The simulation results will provide guidance for device design, manufacturing, and experimental testing. The obtained results and developed circuits can be used as logical building blocks for an Arithmetic-Logic Unit (ALU) and further scaled to more complex digital designs.

Glioblastoma multiforme (GBM) is the most aggressive brain cancer, characterized by a rapid and drug‐resistant progression. GBM “builds” around its primary core a genetically heterogeneous tumor‐microenvironment (TME), recruiting surrounding healthy brain cells by releasing various intercellular signals. Glioma‐associated microglia (GAM) represent the largest population of collaborating cells, which, in the TME, usually exhibit the anti‐inflammatory M2 phenotype, thus promoting an immunosuppressing environment that helps tumor growth. Conversely, “classically activated” M1 microglia could provide proinflammatory and antitumorigenic activity, expected to exert a beneficial effect in defeating glioblastoma. In this work, an immunotherapy approach based on proinflammatory modulation of the GAM phenotype is proposed, through a controlled and localized electrical stimulation. The developed strategy relies on the wireless ultrasonic excitation of polymeric piezoelectric nanoparticles coated with GBM cell membrane extracts, to exploit homotypic targeting in antiglioma applications. Such camouflaged nanotransducers locally generate electrical cues on GAM membranes, activating their M1 phenotype and ultimately triggering a promising anticancer activity. Collected findings open new perspectives in the modulation of immune cell activities through “smart” nanomaterials and, more specifically, provide an innovative auspicious tool in glioma immunotherapy. Glioblastoma multiforme (GBM), the deadliest brain cancer, exhibits rapid and drug‐resistant growth. Its microenvironment recruits healthy brain cells such as the glioma‐associated microglia (GAM), which typically adopt an immunosuppressive M2 phenotype. This study proposes an immunotherapy method using ultrasound‐excited piezoelectric nanoparticles to induce M1 phenotype in GAM, potentially aiding glioblastoma treatment.

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 VGC≃ 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.

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 difficulties limiting their scalability. Surprisingly, electric field modulation of a 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 Isis suppressed 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.

We demonstrate proximity-based all-metallicmesoscopic superconductor-normal metal-superconductor (SNS) field-effect controlled Josephson transistors (SNS-FETs) and show their full characterization from the critical temperature Tcdown to 50 mK in the presence of both electric and magnetic fields. The ability of a static electric field—applied by means of a lateral gate electrode—to suppress the critical current Isin a proximity-induced superconductor is proven for both positive and negative gate voltage values. Isreached 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 syntheticproximity-induced superconductors.

A superconductor with a spin–split excitation spectrum behaves as an ideal ferromagnetic spin-injector in a tunneling junction. It was theoretically predicted that the combination of two such spin–split superconductors with independently tunable magnetizations may be used as an ideal absolute spin-valve. Here, we report on the first switchable superconducting spin-valve based on two EuS/Al bilayers coupled through an aluminum oxide tunnel barrier. The spin-valve shows a relative resistance change between the parallel and antiparallel configuration of the EuS layers up to 900% that demonstrates a highly spin-polarized current through the junction. Our device may be pivotal for realization of thermoelectric radiation detectors, a logical element for a memory cell in cryogenics, superconductor-based computers, and superconducting spintronics in general.

In their original formulation of superconductivity, the London brothers predicted1the exponential suppression of an electrostatic field inside a superconductor over the so-called London penetration depth2–4, λL. Despite a few experiments indicating hints of perturbation induced by electrostatic fields5–7, no clue has been provided so far on the possibility to manipulate metallic superconductors via the field effect. Here, we report field-effect control of the supercurrent in all-metallic transistors made of different Bardeen–Cooper–Schrieffer superconducting thin films. At low temperature, our field-effect transistors show a monotonic decay of the critical current under increasing electrostatic field up to total quenching for gate voltage values as large as ±40 V in titanium-based devices. This bipolar field effect persists up to ~85% of the critical temperature (~0.41 K), and in the presence of sizable magnetic fields. A similar behaviour is observed in aluminium thin-film field-effect transistors. A phenomenological theory accounts for our observations, and points towards the interpretation in terms of an electric-field-induced perturbation propagating inside the superconducting film. In our understanding, this affects the pairing potential and quenches the supercurrent. These results could represent a groundbreaking asset for the realization of all-metallic superconducting field-effect electronics and leading-edge quantum information architectures8,9. A superconducting field-effect transistor was demonstrated with a structure made of different Bardeen–Cooper–Schrieffer superconductors.

Superconducting field-effect transitor (SuFET) and Josephson field-effect transistor (JoFET) technologies take advantage of electric-field-induced control of charge-carrier concentration to modulate the channel superconducting properties. Despite the fact that the field-effect is believed to be ineffective for superconducting metals, recent experiments showed electric-field-dependent modulation of the critical current (IC) in a fully metallic transistor. However, 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 the ICof the superconducting channel. Our easy fabrication process for DB–FETs show symmetric full suppression of ICfor applied critical gate voltages as low as VGC≃ ±8 V at temperatures reaching about the 85% of the record critical temperature, TC≃ 550 mK, for titanium. The gate-independent TCand normal-state resistance (RN) coupled with the increase of resistance in the superconducting state (RS) for gate voltages close to the critical value (VGC) suggest the creation of field-effect induced metallic puddles in the superconducting sea. Our devices show extremely high values of transconductance (|gmMAX| ≃ 15 μA/V at VG≃ ±6.5 V) and variations of Josephson kinetic inductance (LK) with VGof 2 orders of magnitude. Therefore, the DB–FET appears as an ideal candidate for the realization of superconducting electronics, superconducting qubits, and tunable interferometers as well as photon detectors.

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 ∼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.