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Bipolar Thermoelectric Josephson Engine [article]

Gaia Germanese, Federico Paolucci, Giampiero Marchegiani, Alessandro Braggio, Francesco Giazotto
2022 arXiv   pre-print
Thermoelectric effects in metals are typically small due to the nearly-perfect particle-hole (PH) symmetry around their Fermi surface [1, 2]. Despite being initially considered paradoxical [3], thermophase effects [4-8] and linear thermoelectricity [9] in superconducting systems were identified only when PH symmetry is explicitly broken [10-14]. Here, we experimentally demonstrate that a superconducting tunnel junction can develop a very large bipolar thermoelectric effect in the presence of a
more » ... onlinear thermal gradient thanks to spontaneous PH symmetry breaking [15]. Our junctions show a maximum thermovoltage of ±150 μ V at ±650 mK, directly proportional to the superconducting gap. Notably, the corresponding Seebeck coefficient of ±300 μV/K is roughly 10^5 times larger than the one expected for a normal metal at the same temperature [16, 17]. Moreover, by integrating our junctions into a Josephson interferometer, we realize a bipolar thermoelectric Josephson engine (BTJE) [18] with phase-coherent thermopower control [19]. When connected to a generic load, the BTJE generates a phase-tunable electric power up to about 140 mW/m^2 at subKelvin temperatures. In addition, our device implements the prototype for a persistent thermoelectric memory cell, written or erased by current injection [20]. We expect that our findings will trigger thermoelectricity in PH symmetric systems, and will lead to a number of groundbreaking applications in superconducting electronics [21], cutting-edge quantum technologies [22-24] and sensing [25].
arXiv:2202.02121v2 fatcat:f234vp64cvb73oyo5na3wobcbe

Nonlocal thermoelectricity in a topological Andreev interferometer [article]

Gianmichele Blasi, Fabio Taddei, Liliana Arrachea, Matteo Carrega, Alessandro Braggio
2020 arXiv   pre-print
We discuss the phase dependent nonlocal thermoelectric effect in a topological Josephson junction in contact with a normal-metal probe. We show that, due to the helical nature of topological edge states, nonlocal thermoelectricity is generated by a purely Andreev interferometric mechanism. This response can be tuned by imposing a Josephson phase difference, through the application of a dissipationless current between the two superconductors, even without the need of applying an external
more » ... field. We discuss in detail the origin of this effect and we provide also a realistic estimation of the nonlocal Seebeck coefficient that results of the order of few μ V/K.
arXiv:2007.16183v1 fatcat:m64q6c4h5nf75fibaqyz5yd46y

Topological Josephson Heat Engine [article]

Benedikt Scharf, Alessandro Braggio, Elia Strambini, Francesco Giazotto, Ewelina M. Hankiewicz
2020 arXiv   pre-print
The promise of fault-tolerant quantum computing has made topological superconductors the focus of intense research during the past decade. In this context, topological Josephson junctions based on nanowires or on topological insulators provide an alternative route for probing topological superconductivity. As a hallmark of their topological nature, such junctions exhibit a ground-state fermion parity that is 4π-periodic in the superconducting phase difference ϕ. Finding unambiguous experimental
more » ... evidence for this 4π-periodicity still proves a difficult task, however. Here we propose a topological Josephson heat engine implemented by a Josephson-Stirling cycle as an alternative thermodynamic approach to test the ground-state parity. Using a Josephson junction based on a quantum spin Hall (QSH) insulator, we show how the thermodynamic cycle can be used to test the 4π-periodicity of the topological ground state and to distinguish between parity-conserving and non-parity-conserving engines. Interestingly, we find that parity conservation generally boosts both the efficiency and power of the topological heat engine with respect to its non-topological counterpart. Our results, applicable not only to QSH-based junctions but also to any topological Josephson junction, demonstrate the potential of the intriguing and fruitful marriage between topology and coherent thermodynamics.
arXiv:2002.05492v1 fatcat:aj4fqdlvhjfw3mp2gyj7cg5gsa

Nonlocal thermoelectric engines in hybrid topological Josephson junctions [article]

Gianmichele Blasi, Fabio Taddei, Liliana Arrachea, Matteo Carrega, Alessandro Braggio
2021 arXiv   pre-print
The thermoelectric performance of a topological Josephson nonlocal heat engine is thoroughly investigated. The nonlocal response is obtained by using a normal metal probe coupled with only one of the proximized helical edges in the middle of the junction. In this configuration, we investigate how the flux bias and the phase bias trigger the nonlocal thermoelectric effects under the application of a thermal difference between the superconducting terminals. Possible experimental nonidealities
more » ... as asymmetric proximized superconducting gaps are considered showing how the nonlocal response can be affected. The interplay between Doppler-shift, which tends to close gaps, and Andreev interferometry, which affects particle-hole resonant transport, are clearly identified for different operating regimes. Finally, we discuss the power and the efficiency of the topological thermoelectric engine which reaches maximum power at maximal efficiency for a well coupled normal probe. We find quite high nonlocal Seebeck coefficient of the order of tenths of μV/K at a few kelvin, a signal that would be clearly detectable also against any spurious local effect even with moderate asymmetry of the gaps.
arXiv:2103.14394v1 fatcat:dkcehiycbbg45dwiy3oljlxyle

Topological Josephson heat engine

Benedikt Scharf, Alessandro Braggio, Elia Strambini, Francesco Giazotto, Ewelina M. Hankiewicz
2020 Communications Physics  
Topological superconductors represent a fruitful playing ground for fundamental research as well as for potential applications in fault-tolerant quantum computing. Especially Josephson junctions based on topological superconductors remain intensely studied, both theoretically and experimentally. The characteristic property of these junctions is their 4π-periodic ground-state fermion parity in the superconducting phase difference. Using such topological Josephson junctions, we introduce the
more » ... pt of a topological Josephson heat engine. We discuss how this engine can be implemented as a Josephson–Stirling cycle in topological superconductors, thereby illustrating the potential of the intriguing and fruitful marriage between topology and coherent thermodynamics. It is shown that the Josephson–Stirling cycle constitutes a highly versatile thermodynamic machine with different modes of operation controlled by the cycle temperatures. Finally, the thermodynamic cycle reflects the hallmark 4π-periodicity of topological Josephson junctions and could therefore be envisioned as a complementary approach to test topological superconductivity.
doi:10.1038/s42005-020-00463-6 fatcat:5wb366gdmvh7lmtb4lzlcbqzke

Josephson threshold calorimeter [article]

Claudio Guarcello, Alessandro Braggio, Paolo Solinas, Giovanni Piero Pepe, Francesco Giazotto
2019 arXiv   pre-print
We suggest a single-photon thermal detector based on the abrupt jump of the critical current of a temperature-biased tunnel Josephson junction formed by different superconductors, working in the dissipationless regime. The electrode with the lower critical temperature is used as radiation sensing element, so it is kept thermally floating and is connected to an antenna. The warming up resulting from the absorption of a photon can induce a drastic measurable enhancement of the critical current of
more » ... the junction. We propose a detection scheme based on a threshold mechanism for single- or multi-photon detection. This Josephson threshold detector has indeed calorimetric capabilities being able to discriminate the energy of the incident photon. So, for the realistic setup that we discuss, our detector can efficiently work as a calorimeter for photons from the mid infrared, through the optical, into the ultraviolet, specifically, for photons with frequencies in the range [30-9×10^4] THz. In the whole range of detectable frequencies a resolving power significantly larger than one results. In order to reveal the signal, we suggest the fast measurement of the Josephson kinetic inductance. Indeed, the photon-induced change in the critical current affects the Josephson kinetic inductance of the junction, which can be non-invasively read through a LC tank circuit, inductively coupled to the junction. Finally, this readout scheme shows remarkable multiplexing capabilities.
arXiv:1901.01456v2 fatcat:hsmfufa2qjgqtpczjwsql4k7vq

Thermodynamics in topological Josephson junctions [article]

Benedikt Scharf, Alessandro Braggio, Elia Strambini, Francesco Giazotto, Ewelina M. Hankiewicz
2021 arXiv   pre-print
We study the thermodynamic properties of topological Josephson junctions using a quantum spin Hall (QSH) insulator-based junction as an example. In particular, we propose that phase-dependent measurements of the heat capacity offer an alternative to Josephson-current measurements to demonstrate key topological features. Even in an equilibrium situation, where the fermion parity is not conserved, the heat capacity exhibits a pronounced double peak in its phase dependence as a signature of the
more » ... tected zero-energy crossing in the Andreev spectrum. This double-peak feature is robust against changes of the tunneling barrier and thus allows one to distinguish between topological and trivial junctions. At short time scales fermion parity is conserved and the heat capacity is 4π-periodic in the superconducting phase difference. We propose a dispersive setup coupling the Josephson junction to a tank LC circuit to measure the heat capacity of the QSH-based Josephson junction sufficiently fast to detect the 4π-periodicity. Although explicitly calculated for a short QSH-based Josephson junction, our results are also applicable to long as well as nanowire-based topological Josephson junctions.
arXiv:2103.10923v1 fatcat:oq634upupzeelm23yppcnq4rgu

Temperature-biased double-loop Josephson flux transducer [article]

Claudio Guarcello, Roberta Citro, Francesco Giazotto, Alessandro Braggio
2022 arXiv   pre-print
We theoretically study the behavior of the critical current of a thermally-biased tunnel Josephson junction with a particular design, in which the electrodes of the junction are enclosed in two different superconducting loops pierced by independent magnetic fluxes. In this setup, the superconducting gaps can be modified independently through the magnetic fluxes threading the loops. We investigate the response of the device as a function of the magnetic fluxes, by changing the asymmetry
more » ... , i.e., the ratio between the zero-temperature superconducting gaps δ=Δ_10/Δ_20, and the temperatures of the two rings. We demonstrate a magnetically controllable step-like response of the critical current, which emerges even in a symmetric junction, δ=1. Finally, we discuss the optimal working conditions and the high response of the critical current to small changes in the magnetic flux, reporting good performances of the transducer, with a high transfer function that depends on the operating point and the quality of the junction.
arXiv:2110.10585v2 fatcat:rcxymsbtazfb5e3selqo2njo3y

Manipulation of Cooper Pair Entanglement in Hybrid Topological Josephson Junctions

Gianmichele Blasi, Fabio Taddei, Vittorio Giovannetti, Alessandro Braggio
2019 Proceedings (MDPI)  
The non-local manipulation of spin-entangled states by means of local gating in two parallel 2D topological insulators properly connected to two superconducting electrodes is studied. We calculate analytically the current-phase relationship of the Josephson current making use of the scattering matrix approach and we identify the various local and non-local scattering mechanisms. We show that the Josephson critical current, remarkably, allows a direct quantification of the entanglement manipulation.
doi:10.3390/proceedings2019012044 fatcat:6inosqbnenexlapxsmc2b2ej6m

Thermo-electric transport in gauge/gravity models

Andrea Amoretti, Alessandro Braggio, Nicola Maggiore, Nicodemo Magnoli
2017 Advances in Physics: X  
In this review, we summarize recent results in the study of the thermo-electric transport properties of holographic models exhibiting mechanism of momentum dissipation. These models are of particular interests if applied to understand the transport mechanisms of strongly coupled condensed matter systems such as the high-temperature superconductors. After a brief introduction in which we point out the discrepancies between the experimentally measured transport properties of these materials and
more » ... e prediction of the weakly coupled theory of Fermi Liquid, we will review the basic aspects of AdS/CFT correspondence and how gravitational models could help in understanding the peculiar properties of strongly coupled condensed matter systems. ARTICLE HISTORY
doi:10.1080/23746149.2017.1300509 fatcat:a35fvjcgzbgbzlx5ovxtj6ylzy

Thermodynamic cycles in Josephson junctions

Francesco Vischi, Matteo Carrega, Pauli Virtanen, Elia Strambini, Alessandro Braggio, Francesco Giazotto
2019 Scientific Reports  
A superconductor/normal metal/superconductor Josephson junction is a coherent electron system where the thermodynamic entropy depends on temperature and difference of phase across the weak-link. Here, exploiting the phase-temperature thermodynamic diagram of a thermally isolated system, we argue that a cooling effect can be achieved when the phase drop across the junction is brought from 0 to π in a iso-entropic process. We show that iso-entropic cooling can be enhanced with proper choice of
more » ... metrical and electrical parameters of the junction, i.e. by increasing the ratio between supercurrent and total junction volume. We present extensive numerical calculations using quasi-classical Green function methods for a short junction and we compare them with analytical results. Interestingly, we demonstrate that phase-coherent thermodynamic cycles can be implemented by combining iso-entropic and iso-phasic processes acting on the weak-link, thereby engineering the coherent version of thermal machines such as engines and cooling systems. We therefore evaluate their performances and the minimum temperature achievable in a cooling cycle.
doi:10.1038/s41598-019-40202-8 pmid:30824818 pmcid:PMC6397278 fatcat:jd32nnnqdrgwhmyahoquynqbqu

Thermal flux-flow regime in long Josephson tunnel junctions [article]

Claudio Guarcello, Paolo Solinas, Francesco Giazotto, Alessandro Braggio
2019 arXiv   pre-print
We study thermal transport induced by soliton dynamics in a long Josephson tunnel junction operating in the flux-flow regime. A thermal bias across the junction is established by imposing the superconducting electrodes to reside at different temperatures, when solitons flow along the junction. Here, we consider the effect of both a bias current and an external magnetic field on the thermal evolution of the device. In the flux-flow regime, a chain of magnetically-excited solitons rapidly moves
more » ... ong the junction driven by the bias current. We explore the range of bias current triggering the flux-flow regime at fixed values of magnetic field, and the stationary temperature distribution in this operation mode. We evidence a steady multi-peaked temperature profile which reflects on the average soliton distribution along the junction. Finally, we analyse also how the friction affecting the soliton dynamics influences the thermal evolution of the system.
arXiv:1904.13172v1 fatcat:ghtgcyl66ng2hezfpqnyfs5knu

Spontaneous symmetry breaking-induced thermospin effect in superconducting tunnel junctions [article]

Gaia Germanese, Federico Paolucci, Giampiero Marchegiani, Alessandro Braggio, Francesco Giazotto
2021 arXiv   pre-print
We discuss the charge and the spin tunneling currents between two Bardeen-Cooper-Schrieffer (BCS) superconductors, where one density of states is spin-split. In the presence of a large temperature bias across the junction, we predict the generation of a spin-polarized thermoelectric current. This thermo-spin effect is the result of a spontaneous particle-hole symmetry breaking in the absence of a polarizing tunnel barrier. The two spin components, which move in opposite directions, generate a
more » ... in current larger than the purely polarized case when the thermo-active component dominates over the dissipative one.
arXiv:2105.01527v2 fatcat:vzusgvmijvbudlsevx2jnllkfi

Solitonic Josephson Thermal Transport

Claudio Guarcello, Paolo Solinas, Alessandro Braggio, Francesco Giazotto
2018 Physical Review Applied  
We explore the coherent thermal transport sustained by solitons through a long Josephson junction, as a thermal gradient across the system is established. We observe that a soliton causes the heat current through the system to increase. Correspondingly, the junction warms up in correspondence of the soliton, with temperature peaks up to, e.g., approximately 56 mK for a realistic Nb-based proposed setup at a bath temperature Tbath = 4.2 K. The thermal effects on the dynamics of the soliton are
more » ... so discussed. Markedly, this system inherits the topological robustness of the solitons. In view of these results, the proposed device can effectively find an application as a superconducting thermal router in which the thermal transport can be locally mastered through solitonic excitations, which positions can be externally controlled through a magnetic field and a bias current.
doi:10.1103/physrevapplied.9.034014 fatcat:jzlq7crx4fetnhvfor44mtmpuy

rf-SQUID measurements of anomalous Josephson effect [article]

Claudio Guarcello, Roberta Citro, Ofelia Durante, F. Sebastián Bergeret, Andrea Iorio, Cristina Sanz-Fernández, Elia Strambini, Francesco Giazotto, Alessandro Braggio
2020 arXiv   pre-print
We discuss the response of an rf-SQUID formed by anomalous Josephson junctions embedded in a superconducting ring with a non-negligible inductance. We demonstrate that a properly sweeping in-plane magnetic field can cause both the total flux and the current circulating in the device to modulate and to behave hysteretically. The bistable response of the system is analyzed as a function of the anomalous phase shift at different values of the screening parameter, in order to highlight the
more » ... range within which a hysteretic behavior can be observed. The magnetic flux piercing the SQUID ring is demonstrated to further modulate the hysteretical response of the system. Moreover, we show that the anomalous phase shift can be conveniently determined through the measurement of the out-of-plane magnetic field at which the device switches to the voltage state and the number of trapped flux quanta changes. Finally, we compare the response of two different device configurations, namely, a SQUID including only one or two anomalous junctions. In view of these results, the proposed device can be effectively used to detect and measure the anomalous Josephson effect.
arXiv:2001.07621v1 fatcat:iobtvrdpezdy3l6e2n6bptf5uy
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