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“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

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Physical Review Letters features “Sauter-Schwinger Effect in a Bardeen-Cooper-Schrieffer Superconductor” as journal cover

Physical Review Letters features "Sauter-Schwinger Effect in a Bardeen-Cooper-Schrieffer Superconductor" as journal cover Physical Review Letters features “Sauter-Schwinger Effect in a Bardeen-Cooper-Schrieffer Superconductor” as journal cover

Since the 1960s a deep and surprising connection has followed the development of superconductivity and quantum field theory, where the Anderson-Higgs mechanism and the similarities between the Dirac and Bogoliubov–de Gennes equations are the most intriguing examples.

In a recent work “Sauter-Schwinger Effect in a Bardeen-Cooper-Schrieffer Superconductor” published on Physical Review Letters, we follow further this parallelism and show that it predicts an outstanding phenomenon: the superconducting Sauter-Schwinger effect. As in the quantum electrodynamics Schwinger effect, where an electron-positron couple is created from the vacuum by an intense electric field, we show that an electrostatic field can generate two coherent excitations from the superconducting ground-state condensate.

We are glad that our work has been selected for an Editors’ Suggestion and is featured as journal cover of this monthly issue.

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“Gate-Controlled Suspended Titanium Nanobridge Supercurrent Transistor” published on ACS Nano

"Gate-Controlled Suspended Titanium Nanobridge Supercurrent Transistor" published on ACS Nano “Gate-Controlled Suspended Titanium Nanobridge Supercurrent Transistor” published on ACS Nano

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.

A new research carried out at the SQEL add an another piece to this intriguing puzzle showing the control of the supercurrent in fully suspended superconducting nanobridges.

The research, published on ACS Nano by M. Rocci and co-authors, allows to take a different perspective compared to previous studies and promise a better understanding of the field effect in superconducting metals, ruling out some of the hypothesis as possible mechanisms driving for the observed phenomenology.

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“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

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“Nonlinear thermoelectricity with electron-hole symmetric systems” published on Physical Review Letters

“Nonlinear thermoelectricity with electron-hole symmetric systems” published on Physical Review Letters

Recently thermoelectric systems have been extensively investigated since the growing interests in the field of quantum thermodynamics and in studying of thermal transport at the nanoscale.

In a two-terminal system, a necessary condition for thermoelectricity in the linear regime – i.e., for a small voltage V and a small temperature bias ∆T – is breaking the electron-hole symmetry which results in the transport property I(V, ∆T) ≠ −I(−V, ∆T), where I is the charge current flowing through the two-terminal system.

In a new research paper “Nonlinear thermoelectricity with electron-hole symmetric systems” published on “Physical Review Letters” by G. Marchegiani, A. Braggio e F. Giazotto, we demonstrate that this condition is no longer required outside the linear regime. Even a prototype system like a tunnel junction between two different superconductors, can exhibit nonlinear thermo-electric effect based on the spontaneous breaking of electron-hole symmetry in the system.

“The next step will be the experimental realization of this effect and further theoretical investigations of this new discovered mechanism”.

commented F. Giazotto

Check out also the Italian press release!