arXiv subjects

Giacomo Trupiano

Publications and source records attributed to Giacomo Trupiano.

7 recordsLinked to original sources

arXiv2026

A Zero-Bias Superconducting Voltage Amplifier Based on the Bipolar Thermoelectric Effect

We introduce a zero-bias superconducting voltage amplifier that harvests energy from a thermal gradient by exploiting negative differential resistance (NDR) in an asymmetric tunnel junction. The device is based on an asymmetric superconductor-insulator-superconductor (SIS) junction with an energy-gap ratio of $Δ_1/Δ_2 = 0.5$, connected in series with a load resistor. Owing to the superconducting bipolar thermoelectric effect, the current-voltage characteristic of the junction exhibits a region of NDR, in which the net current flows opposite to the applied voltage. This mechanism enables voltage amplification in the absence of any external electrical bias, relying solely on the temperature difference between the electrodes ($T_H \simeq 1$ K, $T_B \simeq 20$ mK). Numerical simulations predict a voltage gain of 20 dB, a 1 dB compression point at an input amplitude of 2 $μ$V, and a total harmonic distortion below $-50$ dB. The input-referred noise is approximately 1 nV/$\sqrt{Hz}$, with an associated thermal load on the order of nanowatts. The frequency response is broadband from near DC, with a $-3$ dB cutoff around 180 MHz, set by the RC time constant of the junction. Using Al-, Al-Cu-, and AlO$_x$-based technologies, the amplifier is compatible with conventional superconducting circuit fabrication processes. These findings demonstrate that thermoelectric superconducting junctions can deliver bias-free voltage amplification from near DC up to about 200 MHz, making them promising candidates for transition-edge sensor readout, quantum circuit instrumentation, and low-frequency cryogenic signal processing.

cond-mat.supr-con↗

arXiv2025

A Thermally Modulated SINIS Trasconductance Amplifier

We introduce a superconducting transconductance amplifier based on the thermal modulation of a SINIS (Superconductor-Insulator-Normal metal-Insulator-Superconductor) configuration. The device is composed of a normal metal island interfaced with two superconducting leads through tunnel barriers, establishing a voltage-biased symmetric SINIS setup. An additional NIS junction connects the island to a third superconducting lead, which serves as input. When the input voltage surpasses the superconducting gap, the resultant injection of quasiparticles increases the electronic temperature of the island, thereby modulating the SINIS current. We perform numerical analyzes of the device performance, influenced by input voltage, frequency, and bath temperature. At bath temperatures below 250 mK, the device shows a transconductance exceeding 4 mS and a current gain exceeding 45 dB. Both gain and transconductance maintain their levels up to 1 MHz, but decrease at higher frequencies, with a -3 dB cutoff around 10 MHz, and an average power dissipation of approximately 5 nW. Our simulations reveal a fully voltage-controlled, three-terminal superconducting amplifier characterized by high transconductance and gain, achieved through thermally mediated signal transduction. This architectural design presents a promising avenue for cryogenic amplification with reduced power dissipation and compatibility with current superconducting electronic systems.

cond-mat.supr-con↗

arXiv2025

Josephson Field Effect Transistors with InAs on Insulator and High Permittivity Gate Dielectrics

InAs on Insulator (InAsOI) has been recently demonstrated as a promising platform to develop hybrid semiconducting-superconducting Josephson Junctions (JJs) and Josephson Field Effect Transistors (JoFETs). The InAsOI consists of an InAs epilayer grown onto a cryogenic-electrically-insulating InAlAs metamorphic buffer, which allows the electrical decoupling of surface-exposed adjacent devices together with a high critical current density integration. The miniaturization of Si microchips has progressed significantly due to the integration of high permittivity (high-k) gate insulators, allowing an increased gate coupling with the transistor channel with consequent reduced gate operating voltages and leakages. As well as for Si-based FETs, integrating high-k gate insulators with JoFETs promises similar advantages in superconducting electronics. Here, we investigate the gate-tunable electrical properties of InAsOI-based JoFETs featuring different high-k gate insulators, namely, HfO2 and Al2O3. We found that both the ungated and gate-tunable electrical properties of the JoFETs are strongly dependent on the insulator chosen. With both dielectrics, the JoFETs can entirely suppress the switching current and increase the normal state resistance by 10-20 times using negative gate voltages. The HfO2-JoFETs exhibit improved gate-tunable electrical performance compared to those achieved with Al2O3-JoFETs, which is related to the higher permittivity of the insulator. Gate-dependent electrical properties of InAsOI-based JoFETs were evaluated in the temperature range from 50 mK to 1 K. Moreover, under the influence of an out-of-plane magnetic field, JoFETs exhibited an unconventional Fraunhofer diffraction pattern, from which an edge-peaked supercurrent density distribution was calculated.

cond-mat.supr-con↗

arXiv2025

Estimation of the FR4 Microwave Dielectric Properties at Cryogenic Temperature for Quantum-Chip-Interface PCBs Design

Ad-hoc interface PCBs (Printed Circuit Boards) 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 fabrication of cryogenic PCBs. Here, we report on an effective way to evaluate the dielectric performance of a FR4 laminate used as substrate for cryogenic microwave PCBs. We designed a coplanar waveguide λ/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 um 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 1.2x10^-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 1.6x^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 to 4 K. The proposed approach can be immediately extended to the detection of cryogenic temperature-dependent dielectric performance of any kind of substrate.

physics.ins-det↗

arXiv2025

InAs on Insulator: A New Platform for Cryogenic Hybrid Superconducting Electronics

Superconducting circuits based on hybrid InAs Josephson Junctions (JJs) play a starring role in the design of fast and ultra-low power consumption solid-state quantum electronics and exploring novel physical phenomena. Conventionally, 3D substrates, 2D quantum wells (QWs), and 1D nanowires (NWs) made of InAs are employed to create superconducting circuits with hybrid JJs. Each platform has its advantages and disadvantages. Here, we proposed the InAs-on-insulator (InAsOI) as a groundbreaking platform for developing superconducting electronics. An epilayer of semiconducting InAs with different electron densities was grown onto an InAlAs metamorphic buffer layer, efficiently used as a cryogenic insulator to decouple adjacent devices electrically. JJs with various lengths and widths were fabricated employing Al as a superconductor and InAs with different electron densities. We achieved a switching current density of 7.3 uA/um, a critical voltage of 50-to-80 uV, and a critical temperature equal to that of the superconductor used. For all the JJs, the switching current follows a characteristic Fraunhofer pattern with an out-of-plane magnetic field. These achievements enable the use of InAsOI to design and fabricate surface-exposed Josephson Field Effect Transistors with high critical current densities and superior gating properties.

cond-mat.supr-con↗

arXiv2024

A quasiparticle-injection superconducting microwave relaxation oscillator

We propose a superconducting microwave relaxation oscillator based on a nanowire shunted by a resistor and an inductor controlled by quasiparticle injection from a tunnel junction positioned on it: the QUISTRON. This device exhibits relaxation oscillator behavior with DC voltage-controlled frequency tuning and DC current bias. The device frequency is modulated via the tunnel junction, which induces localized heating by injecting quasiparticles. This heating mechanism modulates the nanowire switching current, enabling relaxation oscillations when it falls below the bias current. We demonstrate the device operating principles and characterize its performance across various parameters, including different choices of shunt resistor, shunt inductance, and bath temperature ranging from 20 mK to 1 K. The device showed oscillation with a frequency range approximately between 1 GHz and 10 GHz and total energy dissipation per cycle of $\sim100$ zJ. Our results suggest that this design offers a promising platform for compact, tunable superconducting oscillators in the microwave spectrum with potential applications in quantum information processing, microwave technology, and ultra-low-power electronics. The straightforward frequency control mechanism and integration potential make this device an attractive candidate for superconducting microwave local oscillators.

cond-mat.mes-hall↗

arXiv2023

Optical grade bromide-based thin film electrolytes

Controlling the charge density in low-dimensional materials with an electrostatic potential is a powerful tool to explore and influence their electronic and optical properties. Conventional solid gates impose strict geometrical constraints to the devices and often absorb electromagnetic radiation in the infrared (IR) region. A powerful alternative is ionic liquid (IL) gating. This technique only needs a metallic electrode in contact with the IL and the highest achievable electric field is limited by the electrochemical interactions of the IL with the environment. Despite the excellent gating properties, a large number of ILs is hardly exploitable for optical experiments in the mid-IR region, because they typically suffer from low optical transparency and degradation in ambient conditions. Here, we report the realization of two electrolytes based on bromide ILs dissolved in polymethyl methacrylate (PMMA). We demonstrate that such electrolytes can induce state-of-the-art charge densities as high as $20\times10^{15}\ \mathrm{cm^{-2}}$. Thanks to the low water absorption of PMMA, they work both in vacuum and in ambient atmosphere after a simple vacuum curing. Furthermore, our electrolytes can be spin coated into flat thin films with optical transparency in the range from 600 cm$^{-1}$ to 4000 cm$^{-1}$. Thanks to these properties, the electrolytes are excellent candidates to fill the gap as versatile gating layers for electronic and mid-IR optoelectronic devices.

cond-mat.mes-hall↗