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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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“Nonlocal thermoelectricity in a topological Josephson junction” just published on “Physical Review Letters”

Sketch of the setup used to probe the nonlocal Thermoelectricity in a topological Josephson junction Sketch of the setup used to probe the nonlocal Thermoelectricity in a topological Josephson junction

In a paper just published on Physical Review Letters, a NEST-CNR-NANO team lead by SQEL member Alessandro Braggio identified a unique non-local thermoelectrical effect in a Quantum spin Hall system in 2-dimensional topological insulators, proximized with superconductors, also called topological Josephson junctions.

The quantum spin Hall state is characterised by Kramer paired helical edge states which propagate in opposite directions with opposite spin orientations (spin-momentum locking). Unambiguous identification of those edge state is fundamental to certify their topological nature and has prominent implications in condensed matter research and its applications in topological quantum computation and sensing.

The team, composed by Gianmichele Blasi, Fabio Taddei, Matteo Carrega and coordinated by Alessandro Braggio from SQEL and NEST laboratory (Scuola Normale Superiore and CnrNano) collaborating with Liliana Arrachea from ECyT-UNSAM (Argentina), investigated a three-terminal setup with helical edge states proximized by two superconductors and contacted with a normal-metal probe, in the presence of an external magnetic field. Since the whole system is particle-hole symmetric, nonlocality is the only way to generate linear thermoelectricity. Nonlocal thermoelectrical transport is generated in the probe by applying a thermal gradient between the superconductors.

Blasi, G., Taddei, F., Arrachea, L., Carrega, M., & Braggio, A. (2020). Nonlocal Thermoelectricity in a S-TI-S Junction in Contact with a N-Metal Probe: Evidence for Helical Edge States. Physical Review Letters, 124(22), 227701. DOI: https://doi.org/10.1103/PhysRevLett.124.227701. arXiv: http://arxiv.org/abs/1911.04367

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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!

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“Field-Effect Controllable Metallic Josephson Interferometer” published on Nano Letters

“Field-Effect Controllable Metallic Josephson Interferometer” published on Nano Letters “Field-Effect Controllable Metallic Josephson Interferometer” published on Nano Letters

A new research carried out at the SQEL report the realization of a titanium-based monolithic superconducting quantum interference device (SQUID) which can be tuned by applying a gate bias to its two Josephson junctions.

The research, published on Nano Letters by F. Paolucci and co-authors, points out the strong implications of the apparent coupling of a static electric field to the macroscopic phase of the superconducting condensate.

Beyond that, this class of quantum interferometers could represent a breakthrough for several applications such as digital electronics, quantum computing, sensitive magnetometry, and single-photon detection.

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Josephson Field-Effect Transistors Based on All-Metallic Al/Cu/Al Proximity Nanojunctions

"Josephson Field-Effect Transistors Based on All-Metallic Al/Cu/Al Proximity Nanojunctions" published on ACS Nano “Josephson Field-Effect Transistors Based on All-Metallic Al/Cu/Al Proximity Nanojunctions” published on ACS Nano

Researchers from SQEL have just realized field-effect controlled Josephson transistors based on proximity all-metallic mesoscopic superconductor-normal metal-superconductor junctions.

The research, published on ACS Nano by G. De Simoni and co-authors, suggests that the mechanism at the basis of the superconducting field-effect 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 synthetic proximity-induced superconductors.