Thermoelectricity in a tunnel junction between superconductors  

Pisa - 16.03.2020 - Thermoelectricity in a tunnel junction between superconductors
In an article published in Physical Review Letters, researchers from Cnr-Nano identified a new mechanism of thermoelectricity in superconducting materials, for which it was thought to be "impossible".
The study, conducted by Giampiero Marchegiani, Alessandro Braggio and Francesco Giazotto at the NEST laboratory of Cnr-Nano and Scuola Normale Superiore, allows to study new ways of generating thermoelectricity and opens up the realization of thermoelectric memories, ultra-sensitive detectors or other quantum technologies.

Thermoelectricity as spontaneous breaking of electron-hole symmetry:
Thermoelectricity is the fundamental property of physical systems to generate electrical signals in response to temperature gradients. Typically in the linear regime, namely for small temperature differences, the thermal diffusion of the dominant carriers induces a charge accumulation and consequently a generation of a voltage bias at open circuit (Seebeck voltage). So, for systems that satisfy the electron-hole symmetry, this implies the absence of linear thermoelectricity. CnrNano researchers identified a universal mechanism for a system where two electron-hole symmetric electrodes are coupled through tunnelling and they still generate thermoelectricity in the nonlinear temperature regime. In particular, scientists provided general and sufficient conditions for absolute negative conductance and thermoelectric power generation at finite voltage-bias. They investigated the effect in an experimentally relevant setting: a junction between two different superconductors. Due to symmetry, the system presents a by-stable Seebeck voltage for a given fixed temperature bias, namely, thermoelectricity arises from spontaneous breaking of the electron-hole symmetry. This result could open a new route for thermoelectrical generation, sensors, and applications.

Nonlinear Thermoelectricity with Electron-Hole Symmetric Systems, G. Marchegiani, A. Braggio, and F. Giazotto, Phys. Rev. Lett. 124, 106801 – Published 10 March 2020



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