Non-hysteretic superconducting quantum interference proximity transistor with enhanced responsivity

Jabdaraghi, Robab Najafi; Meschke, Matthias; Pekola, Jukka P.

doi:10.1063/1.4866584

Cited by 20 publications

(43 citation statements)

References 35 publications

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“…According to the above conditions the experimental realization of our thermal nanovalve can be easily achieved with conventional metals and standard lithographic techniques [9][10][11][12] . Superconducting tunnel junctions additionally coupled to the SN ring and the N 1 electrode, serving either as heaters or thermometers, allow to change and monitor the quasiparticle temperature on both sides of the structure 27 .…”

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confidence: 99%

“…Here we propose an alternative approach to control heat transport by envisioning a thermal nanovalve based on proximity effect but phase-controlled by a SQUIPT [9][10][11][12] . Differing from SQUID-based and Andreev interferometers our device allows a drastic quenching of the thermal conductance which makes our proposal an efficient phase-tunable thermal nanovalve.…”

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Proximity nanovalve with large phase-tunable thermal conductance

Strambini

Bergeret

Giazotto

2014

Applied Physics Letters

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We propose a phase-controlled heat-flux quantum valve based on the proximity effect driven by a superconducting quantum interference proximity transistor (SQUIPT). Its operation relies on the phase-dependent quasiparticle density of states in the Josephson weak-link of the SQUIPT which controls thermal transport across the device. In a realistic Al/Cu-based setup the structure can provide efficient control of thermal current inducing temperature swings exceeding ∼ 100 mK, and flux-to-temperature transfer coefficients up to ∼ 500 mK/Φ 0 below 100 mK. The nanovalve performances improve by lowering the bath temperature, making the proposed structure a promising building-block for the implementation of coherent caloritronic devices operating below 1 K.Phase-dependent manipulation of heat in solid-state nanodevices is nowadays one of the major challenges of coherent caloritronics 1 , and plays a key role in determining the physical properties of mesoscopic systems at low temperature. Toward this direction, the prototype for a heat interferometer has been recently realized with a superconducting quantum interference device (SQUID) where the modulation of the thermal current has been achieved thanks to the Josephson coupling 2-5 . Yet, phase-dependent thermal transport has been also demonstrated in Andreev interferometers 6-8 where the proximity effect in a normal metal affects its thermal conductance, and is controlled via a magnetic field.Here we propose an alternative approach to control heat transport by envisioning a thermal nanovalve based on proximity effect but phase-controlled by a SQUIPT 9-12 . Differing from SQUID-based and Andreev interferometers our device allows a drastic quenching of the thermal conductance which makes our proposal an efficient phase-tunable thermal nanovalve. Specifically, we expect an improvement of the temperature swing (up to ∼ 100 mK) and a flux-to-temperature transfer function exceeding 500 mK/Φ 0 at 100 mK.A sketch for the proximity nanovalve is shown in Fig. 1(a) and consists of a SQUIPT composed by a superconducting (S) ring interrupted by a diffusive normal metal (N) wire of length L. We assume the wire transverse dimensions to be negligible in comparison to its length so that it can be considered as quasi-onedimensional. Superconducting correlations are induced in the N wire owing to proximity effect from the S loop a) Electronic

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Proximity nanovalve with large phase-tunable thermal conductance

Strambini

Bergeret

Giazotto

2014

Applied Physics Letters

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“…It would not be possible to make justice to the vast literature on the subject; some examples are Refs. [6][7][8][9][10][11][12][13][14][15][16][17][18].…”

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confidence: 99%

The Stationary SQUID

Berger

2018

J Low Temp Phys

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In the customary mode of operation of a SQUID, the electromagnetic field in the SQUID is an oscillatory function of time. In this situation, electromagnetic radiation is emitted, and couples to the sample. This is a back-action that can alter the state that we intend to measure. A circuit that could perform as a stationary SQUID consists of a loop of superconducting material that encloses the magnetic flux, connected to a superconducting and to a normal electrode. This circuit does not contain Josephson junctions, or any other miniature feature. We study the evolution of the order parameter and of the electrochemical potential in this circuit; they converge to a stationary regime and the voltage between the electrodes depends on the enclosed flux. We obtain expressions for the power dissipation and for the heat transported by the electric current; the validity of these expressions does not rely on a particular evolution model for the order parameter. We evaluate the influence of fluctuations. For a SQUID perimeter of the order of 1µm and temperature 0.9T c , we obtain a flux resolution of the order of 10 −5 Φ 0 /Hz 1/2 ; the resolution is expected to improve as the temperature is lowered.

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“…Therefore, the probability for electrons to tunnel between N and S R depends on the sign of the spin. The device resembles the superconducting quantum interference proximity transistor (SQUIPT) [8][9][10][11][12] which has been well-studied in several experiments; the crucial structural difference in our device is that the thermoelectric transistor lies in the presence of the FI layer.…”

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“…22,24 Its advantage is the higher critical temperature of NbN of 15 K. As for the normal metal bridge, it is important to achieve good electric contact with the S R loop in order to develop a sizeable and tunable proximity gap. If, for instance, one uses Al as superconductor for the ring, suitable candidates for the N wire are copper (Cu) 8,9,11,12 or silver (Ag) 29 .…”

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Proposal for a phase-coherent thermoelectric transistor

Giazotto

Robinson

Moodera

et al. 2014

Applied Physics Letters

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Identifying materials and devices which offer efficient thermoelectric effects at low temperature is a major obstacle for the development of thermal management strategies for low-temperature electronic systems. Superconductors cannot offer a solution since their near perfect electron-hole symmetry leads to a negligible thermoelectric response; however, here we demonstrate theoretically a superconducting thermoelectric transistor which offers unparalleled figures of merit of up to ∼ 45 and Seebeck coefficients as large as a few mV/K at sub-Kelvin temperatures. The device is also phasetunable meaning its thermoelectric response for power generation can be precisely controlled with a small magnetic field. Our concept is based on a superconductor-normal metal-superconductor interferometer in which the normal metal weak-link is tunnel coupled to a ferromagnetic insulator and a Zeeman split superconductor . Upon application of an external magnetic flux, the interferometer enables phase-coherent manipulation of thermoelectric properties whilst offering efficiencies which approach the Carnot limit.It is known that electron-hole symmetry breaking is essential for a material to posses a finite thermoelectric figure of merit 1,2 . In principle, conventional superconductors have a near perfect symmetric spectrum and therefore are not suitable for thermoelectric devices. However, if the density of states is spin-split by a Zeeman field a superconductor-ferromagnet hybrid device can provide a thermoelectric effect 3-5 with a figure of merit close to 1. Here we propose a multifunctional phase-coherent superconducting transistor in which the thermoelectric efficiency is tunable through an externally applied magnetic flux. A giant Seebeck coefficient of several mV/K and a figure of merit close to ∼ 45 is predicted for realistic materials parameters and materials combinations.The phase-coherent thermoelectric transistor is based on two building blocks. The first one is sketched in Fig. 1(a) and consists of a superconducting film (S R ) tunnel-coupled to a normal metal (N) by a ferromagnetic insulator (FI). The latter induces an exchange field (h) in S R which leads to a Zeeman spin-split superconducting DoS. The spectrum for spin-up (↑) and spin-down (↓) electrons is given bywhere| is the conventional Bardeen-Cooper-Schrieffer DoS in a superconductor, E is the energy, ∆ R is the order parameter, and Γ accounts for broadening. Due to the presence of the spin-splitting field, ∆ R depends on temperature (T ) and h. While the total DoS of S R , ν S R (E) = ν S R↑ (E) + ν S R↓ (E), is electron-hole symmetric [ Fig. 1(b)], the spin-dependent a) Electronic mail: giazotto@sns.it b) Electronic mail: jjr33@cam.ac.uk c) Electronic mail: sebastian bergeret@ehu.es ν S R↑(↓) (E) components are no longer even functions of the energy. This means that electron-hole imbalance can, in principle, be achieved using a spin-filter contact with a normal metal. This would yield a finite thermoelectric effect 3,4 in the N/FI/S R heterostructure shown in F...

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Non-hysteretic superconducting quantum interference proximity transistor with enhanced responsivity

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Cited by 20 publications

References 35 publications

Proximity nanovalve with large phase-tunable thermal conductance

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