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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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SQEL project TERASEC funded with an ERC PoC grant

SQEL project TERASEC funded with an ERC PoC grant SQEL project TERASEC funded with an ERC PoC grant

Among the 76 recipients of the ERC Proof of Concept grants – third round 2019, the TERASEC project will develop an innovative device for the detection of security threats of European citizens and infrastructures

The researcher will receive a €150,000 grant to explore the innovation potential of its project and bring the results closer to market: the goal of the project is to deliver an unrivalled novel security scanner device leveraging harmless THz waves, that widely overpasses the accuracy performances of all the conventional systems, thus contributing to the safety of European citizens and the security of sensitive infrastructures. 

The objectives of TERASEC project entail the activities aimed at pre-commercial validation of the technological performances and market potential of a novel device for the detection of security threats, such as weapons, explosives, drugs etc.”

says F. Giazotto, SQEL and TERASEC principal investigator

The functionality of the system is enabled through combination of superconducting and ferromagnetic materials that delivers frequency selective THz sensors showing unprecedented sensitivity (single-photon resolution), fast response time, high dynamic range, and low noise-equivalent-power. 

Specifically, starting from the outstanding outcomes reached so far, the capacity of the TERASEC system to detect the above threats with given level of accuracy, range and selectivity will be verified in accordance with the requirements of prospect users, to be collected during the project implementation. Moreover, a detailed market, IPR and regulatory compliance study will be carried out, in order to enable smooth implementation of TERASEC in the complicated context of the public security market. To enhance this, an advisory board gathering Key opinion leaders of the sector will be secured and involved into project activity throughout all the project duration. In parallel, comprehensive communication strategy addressing all the stakeholders of the relevant value chain will be rolled out, with strong focus on prospect consumers and users, so to ensuring market traction.”

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Welcome to SQEL Vittorio, Gaia and Mirko!

From left to right: Vittorio Buccheri, Gaia Germanese and Mirko Rocci From left to right: Vittorio Buccheri, Gaia Germanese and Mirko Rocci

We are glad to welcome Vittorio who, after a master project in our group, is back with us for this year, Gaia a new PhD student at the University of Pisa and Mirko who joined us after his stay at MIT.

Vittorio and Gaia will both work on the T-CONVERSE project, for the realization of temperature-to-phase superconducting photodetectors, while Mirko is going to spend the second year of his EuSuper Marie Curie fellowship working on the realization of europium-based superconducting magnetic RAM.

Welcome again and good work!

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Nadia Ligato awarded at “RAITH Micrograph Award 2019”

The winning micrograph: a superconducting quantum interference proximity transistor with multi tunnel junctions. The winning micrograph: a superconducting quantum interference proximity transistor with multi tunnel junctions.

A new recognition of the SQEL cutting-edge research has been given by Raith Nanofabrication to our researcher Nadia Ligato who won the third prize of the RAITH Micrograph Award 2019!

The micrograph winning the award pictures a superconducting quantum interference proximity transistor (SQUIPT), a multi-tunnel junctions device fabricated using electron beam lithography technique and shadow-angle evaporation.

Many compliments to Nadia and stay tuned to not miss new updates about her work!