Thermopower in mesoscopic normal–superconducting structures (original) (raw)
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EPL (Europhysics Letters), 2019
We have studied thermoelectric effect of a Kane-Mele normal-insulator-superconductor (KMNIS) junction at ultra-low temperatures using a modified version of the well-known Blonder-Tinkham-Klapwijk (BTK) theory. Since both the (electronic) charge and thermal current due to the carriers are sensitive to the strengths of the spin-orbit coupling (SOC) present in the Kane-Mele model, a tunability of this junction device with regard to its thermoelectric properties can be experimentally achieved by certain techniques that are used to manipulate the values of the spin-orbit couplings. We have computed the Seebeck coefficient, the Figure of Merit, the thermoelectric cooling, the coefficient of performance of the KMNIS junction as a self-cooling device and investigated the role of the Rashba SOC (RSOC) and intrinsic SOC (ISOC) parameters therein. Our results on the thermoelectric cooling indicate practical realizability and usefulness for efficient cooling detectors, sensors, and quantum devices and hence could be crucial to experimental success of the thermoelectric applications of such junction devices. Further we have briefly touched upon the condition that distinguishes transmission through a topological insulator from an ordinary one.
Low-temperature thermal properties of mesoscopic normal-metal/superconductor heterostructures
Physical Review B, 2001
Although the electrical transport properties of mesoscopic metallic samples have been investigated extensively over the past two decades, the thermal properties have received far less attention. This may be due in part to the difficulty of performing thermal measurements on sub-micron scale samples. We report here quantitative measurements of the thermal conductance and thermopower of a hybrid normal-metal/superconductor heterostructure, which are made possible by the recent development of a local-thermometry technique. As with electrical transport measurements, these thermal measurements reveal signatures of the phase coherent nature of electron transport in these devices.
Theory of thermoelectric phenomena in superconductors
Physical Review B, 2002
The theory of thermoelectric effects in superconductors is discussed in connection to the recent publication by Marinescu and Overhauser [Phys. Rev. B 55, 11637 (1997)]. We argue that the charge non-conservation arguments by Marinescu and Overhauser do not require any revision of the Boltzmann transport equation in superconductors. We show that the charge current proportional to the gradient of the gap, |∆| found by Marinescu and Overhauser, is incompatible with the time-reversal symmetry, and conclude that their "electronconserving transport theory" is invalid. Possible mechanisms responsible for the discrepancy between some experimental data and the theory by Galperin, Gurevich, and Kozub Pis'ma Zh. Eksp. Teor. Fiz. 17, 689 (73) [JETP Lett. 17, 476 (1973)] are discussed.
Journal of Physics: Condensed Matter, 2022
A detailed investigation of the non-equilibrium steady-state electric and thermoelectric transport properties of a quantum dot (QD) coupled to the normal metallic and s-wave superconducting reservoirs (N–QD–S) are provided within the Coulomb blockade regime. Using non-equilibrium Keldysh Green’s function formalism, initially, various model parameter dependences of thermoelectric transport properties are analysed within the linear response regime. It is observed that the single-particle tunnelling close to the superconducting gap edge can generate a relatively large thermopower and figure of merit. Moreover, the Andreev tunnelling plays a significant role in the suppression of thermopower and figure of merit within the gap region. Further, within the non-linear regime, we discuss two different situations, i.e., the finite voltage biasing between isothermal reservoirs and the finite thermal gradient in the context of thermoelectric heat engine. In the former case, it is shown that the...
Anomalous transport in normal-superconducting and ferromagnetic-superconducting nanostructures
Physical Review B, 1999
We have calculated the temperature dependence of the conductance variation (δS(T )) of mesoscopic superconductor normal metal(S/N) structures, in the diffusive regime, analysing both weak and strong proximity effects. We show that in the case of a weak proximity effect there are two peaks in the dependence of δS(T ) on temperature. One of them (known from previous studies) corresponds to a temperature T1 of order of the Thouless energy (ǫ T h ), and another, newly predicted maximum, occurs at a temperature T2 where the energy gap in the superconductor ∆(T2) is of order ǫ T h . In the limit L φ < L the temperature T1 is determined by Dh/L 2 φ (L φ is the phase breaking length), and not ǫ T h . We have also calculated the voltage dependence δS(V ) for a S/F structure (F is a ferromagnet) and predict non-monotonic behaviour at voltages of order the Zeeman splitting.
Thermoelectric Effects in Superconductors
Springer eBooks, 1981
A summary of recent theoretical and experimental work on thermoelectric and related effects in superconductorsis given. Whereas this field for a long time was characterized by large discrepancies between theory and experiment, more recent experiments confirm the theoretical concepts. Experimentswhich investigate the difference between the electrochemical potential of excitations and Cooper pairs (charge imbalance) play a prominent role. They allow one to determine the thermoelectric transport coefficient. Also a new type of thermoelectric effect is discussed: a chargeimbalance is created ifa supercurrentis flowing in the presence of a temperature gradient•
Giant thermoelectric effects in a proximity-coupled superconductor–ferromagnet device
New Journal of Physics, 2014
The usually negligibly small thermoelectric effects in superconducting heterostructures can be boosted dramatically due to the simultaneous effect of spin splitting and spin filtering. Building on an idea of our earlier work [Phys. Rev. Lett. 110, 047002 (2013)], we propose realistic mesoscopic setups to observe thermoelectric effects in superconductor heterostructures with ferromagnetic interfaces or terminals. We focus on the Seebeck effect being a direct measure of the local thermoelectric response and find that a thermopower of the order of ∼ 250 µV /K can be achieved in a transistor-like structure, in which a third terminal allows to drain the thermal current. A measurement of the thermopower can furthermore be used to determine quantitatively the spin-dependent interface parameters that induce the spin splitting. For applications in nanoscale cooling we discuss the figure of merit for which we find values exceeding 1.5 for temperatures 1K.
Large thermoelectric effects in unconventional superconductors
Physical Review B, 2004
We present analytic and numerical results for the thermoelectric effect in unconventional superconductors with a dilute random distribution of impurities, each scattering isotropically but with a phase shift intermediate between the Born and unitary limits. The thermoelectric response function has a linear temperature dependence at low temperatures, with a slope that depends on the impurity concentration and phase shift. Although the thermoelectric effect vanishes identically in the strict Born and unitary limits, even a small deviation of the phase shift from these limits leads to a large response, especially in clean systems. We also discuss possibilities of measuring counter-flowing supercurrents in a SQUID-setup. The non-quantized thermoelectrically induced flux can easily be of the order of a percent of the flux quantum in clean systems at 4 He temperatures.
The Vanishing of Thermoelectric Effects in Superconductors
Journal of Non-Equilibrium Thermodynamics, 2007
It is shown that the vanishing of thermoelectric e¤ects in superconductors is a simple consequence of the positive character of entropy production and of the Onsager relations, if the thermal conductivity of the superconducting sample is finite.
Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions
Beilstein Journal of Nanotechnology, 2016
Background: Thermoelectric effects result from the coupling of charge and heat transport and can be used for thermometry, cooling and harvesting of thermal energy. The microscopic origin of thermoelectric effects is a broken electron–hole symmetry, which is usually quite small in metal structures. In addition, thermoelectric effects decrease towards low temperatures, which usually makes them vanishingly small in metal nanostructures in the sub-Kelvin regime. Results: We report on a combined experimental and theoretical investigation of thermoelectric effects in superconductor/ferromagnet hybrid structures. We investigate the dependence of thermoelectric currents on the thermal excitation, as well as on the presence of a dc bias voltage across the junction. Conclusion: Large thermoelectric effects are observed in superconductor/ferromagnet and superconductor/normal-metal hybrid structures. The spin-independent signals observed under finite voltage bias are shown to be reciprocal to t...