“Bipolar Thermoelectric Josephson Engine” published in Nature Nanotechnology

Bipolar thermoelectric Josephson engine Bipolar thermoelectric Josephson engine

Members of the SQEL team have developed a new type of thermoelectric engine that converts heat into electricity through the Josephson effect. The engine, which the team dubbed the “Bipolar thermoelectric Josephson Engine” is based on the effect of spontaneous particle-hole symmetry breaking in superconducting systems and has been published in the prestigious journal Nature Nanotechnology.

The work, carried out by G. Germanese and coworkers, experimentally demonstrates that superconducting tunnel junctions develop very large bipolar thermoelectricity in the presence of a considerable thermal gradient due to the spontaneous breaking of particle-hole symmetry, a novel concept already studied by other members of SQEL.

Our study is then pivotal for groundbreaking investigations of nonlinear thermoelectric effects in different systems ranging from semiconductors and low-dimensional electronic materials to high-temperature superconductors and topological insulators.

More information: Germanese, G., Paolucci, F., Marchegiani, G. et al. Bipolar thermoelectric Josephson engine. Nat. Nanotechnol. (2022). https://doi.org/10.1038/s41565-022-01208-y

“A thermal superconducting quantum interference proximity transistor ” published on Nature Physics

Thermal superconducting quantum interference proximity transistor Thermal superconducting quantum interference proximity transistor

Researchers at SQEL have recently developed a transistor that takes advantage of this specific quality of superconductors, a thermal superconducting quantum interference proximity transistor (T-SQUIPT) published on Nature Physics.

T-SQUIPT was first theoretically proposed by some of the authors of our recent paper several years ago, although without a concrete realization yet. Our implementation of the T-SQUIPT exploits a long superconducting nanowire as proximitized element thus allowing us to demonstrate the possibility to phase-tune the thermal transport properties of a superconductor and to realize the first thermal memory cell as well.

The core concept of T-SQUIPT is a nanoscopic island of aluminum (Al) that can be made superconducting- or normal metal-like with quantum interference induced by two superconducting leads defining a ring and placed in good metallic contact with the island. For integer values of the flux quantum piercing the superconducting loop, superconductivity is reinforced and the island behaves as a good thermal insulator. For semi-integer values of the flux quantum, superconductivity is ideally suppressed, and the island behaves as a good thermal conductor.

As part of their recent study, SQEL researchers demonstrated this ability of their transistor by sinking heat from a metallic electrode into it, which was also coupled to the aluminum island through a tunnel contact. Overall, our findings demonstrate the feasibility of phase-coherently manipulating the energy transport qualities of quantum devices.

In the future, the T-SQUIPT transistor could pave the way towards the realization of a variety of new devices. The recent paper also enhances the current understanding of energy transfer at the nanoscale, thus potentially improving its management.

More information: Nadia Ligato et al, Thermal superconducting quantum interference proximity transistor, Nature Physics (2022). DOI: 10.1038/s41567-022-01578-z

FETOPEN “SuperGate” funded with a €3M european project

From March 2021, SQEL is going to start a new research and innovation project SuperGate Gate Tuneable Superconducting Quantum Electronics, funded by the European Commission under the HORIZON-2020 FETOPEN program.

The project’s goal is to combine the powerful and energy-efficient superconductor technology with existing semiconductor technology and is based on the path-breaking discovery by the SQEL team that the superconductors can be controlled via electric field effect.

SuperGate is coordinated by the University of Konstanz and, apart from SQEL team institutes CNR-NANO and Scuola Normale Superiore di Pisa, involves CNR-SPIN, University of Salerno, Budapest University of Technology and Economics (HU), Delft University of Technology (NL), Chalmers University of Technology (SE) and SeeQC (IT).

The ultimate goal of SuperGate is to develop a new outperforming technology for superconducting logics that is completely based on electric field effect. The proposed technology promises a disruptive impact and radical transformations in the long term both in the world of supercomputing and concerning the design of innovative devices for quantum technologies.

Read more at the CNR-NANO press release.

“A Josephson phase battery” has been published on “Nature Nanotechnology”

The first quantum phase battery, consisting of an indium arsenide (InAs) nanowire in contact with aluminum superconducting leads. Device concept by Andrea Iorio (SQEL). The first quantum phase battery, consisting of an indium arsenide (InAs) nanowire in contact with aluminum superconducting leads. Device concept by Andrea Iorio (SQEL).

A classical battery converts chemical energy into a persistent voltage bias that can power electronic circuits. Similarly, a phase battery is a quantum device that provides a persistent phase bias to the wave function of a quantum circuit. In a recent experiment carried out at SQEL, E. Strambini and co-workers have demonstrated and realized the first quantum phase battery in a hybrid superconducting circuit. The research, published on Nature Nanotechnology, is the result of an international collaboration which sees involved CNR-Nano, Scuola Normale Superiore, Salerno University in Italy and Material Physics Center (CFM), Donostia International Physics Center (DIPC) in Spain.

The quantum device that we realized is able to provide a persistent phase bias in a superconducting circuit effectively behaving like a quantum phase battery.

says Francesco Giazotto, group leader of SQEL.

The idea was first conceived in 2015, by Sebastian Bergeret and Ilya Tokatly, which proposed a theoretical system with the properties needed to build the phase battery. A few years later Francesco Giazotto and Elia Strambini from SQEL identified a suitable material combination, consisting of an n-doped InAs nanowire forming the core of the battery (the pile) and Al superconducting leads as poles and carried out the experiment at NEST Laboratory.

We found that the ferromagnetic polarization of the unpaired-spin states on the nanowire surface is efficiently converted into a persistent phase bias φ0 across the wire, leading to the anomalous Josephson effect. By applying an external in-plane magnetic field we achieved a continuous tuning of φ0 that persisted also in the absence of the field, thus realizing a phase battery.

comments Elia Strambini, first author of the research.

The next steps will consist in improving the control and performance of the battery by employing new material choices and design. This work contributes to the enormous advances being made in quantum technology that are expected to revolutionize both computing and sensing techniques, as well as medicine, and telecommunications in the near future.

More information:
Strambini, E., Iorio, A., Durante, O. et al. A Josephson phase battery. Nature Nanotechnology (2020). DOI: 10.1038/s41565-020-0712-7, www.nature.com/articles/s41565-020-0712-7