Electronic microrefrigerator based on a normal-insulator-superconductor tunnel junction

Nahum, M.; Eiles, Travis M.; Martinis, John M.

doi:10.1063/1.112456

Cited by 303 publications

(263 citation statements)

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“…[12][13][14][15] At low temperatures k B T and for bias voltages eV across the junction, the electrons in the N electrode cool considerably below the phonon temperature by hot QP extraction. The effect can be made to be more pronounced in a symmetric double-junction SINIS structure with a small N island contacted to S leads via two NIS junctions, 15 allowing to construct practical solid-state refrigerators for cooling thin-film detectors to temperatures close to 100 mK.…”

mentioning

confidence: 99%

Magnetic-field-induced stabilization of nonequilibrium superconductivity in a normal-metal/insulator/superconductor junction

Peltonen¹,

Muhonen

Meschke³

et al. 2011

Phys. Rev. B

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A small magnetic field is found to enhance relaxation processes in a superconductor, thus stabilizing superconductivity in nonequilibrium conditions. In a normal-metal (N)/insulator/superconductor (S) tunnel junction, applying a field of the order of 100 μT leads to significantly improved cooling of the N island by quasiparticle (QP) tunneling. These findings are attributed to faster QP relaxation within the S electrodes as a result of enhanced QP drain through regions with a locally suppressed energy gap due to magnetic vortices in the S leads at some distance from the junction. Introduction. In this Rapid Communication, we report an observation that appears counterintuitive at first: A small magnetic field is found to stabilize superconductivity under quasiparticle (QP) injection. In our experiment, the cooling power of normal-metal (N)/insulator (I)/superconductor (S) tunnel structures is enhanced in perpendicular magnetic fields B ⊥ 100 μT = 1 G. A measured maximum temperature drop δT relative to a starting bath temperature T 0 = 285 mK exhibiting this behavior is shown in Fig. 1(a). The improvement is unexpected, as in general the effect of a magnetic field is to suppress superconductivity. Electronic cooling in NIS junctions in the presence of magnetic fields in both perpendicular and parallel orientations has been studied before, 1 but only in higher fields where the cooling power was already reduced due to a diminishing superconducting energy gap . On the other hand, the creation of magnetic vortices 2 has been shown to enhance QP relaxation in superconducting aluminum, as the QPs become trapped and thermalize in the regions of a reduced energy gap. 3 Here we demonstrate that the additional relaxation channel due to an enhanced QP drain through regions occupied by magnetic vortices enhances the superconducting performance of S leads and improves the electronic cooling in NIS junctions. This can be of relevance in superconducting qubits, 4-7 resonators, 8 and in hybrid SINIS turnstiles 9 in reducing the effects from nonequilibrium and residual QPs arising due to drive and microwave radiation from the environment. Moreover, improved relaxation caused by vortex creation in the S leads can partially explain the "reentrant superconductivity" observed in Zn and Al nanowires. 10,11 In the present case, as sketched in Fig. 1(a), vortex formation in the S electrodes away from the NIS junction improves relaxation of the injected QPs and leads to enhanced cooling of the N island. In higher fields, vortices move closer to the junction, deteriorating the cooling power.In a NIS junction, acts as an energy filter for the tunneling QP. [12][13][14][15] At low temperatures k B T and for bias voltages eV across the junction, the electrons in the N electrode cool considerably below the phonon temperature by hot QP extraction. The effect can be made to be more pronounced in a symmetric double-junction SINIS structure with a small N

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confidence: 99%

Magnetic-field-induced stabilization of nonequilibrium superconductivity in a normal-metal/insulator/superconductor junction

Peltonen¹,

Muhonen

Meschke³

et al. 2011

Phys. Rev. B

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“…This is the case in the experiments reported in [8]. The Fermi energy of the central island is aligned with the edge of the gap of one of the superconducting electrodes.…”

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confidence: 57%

“…The Fermi energy of the central island is aligned with the edge of the gap of one of the superconducting electrodes. Thus, the process studied here can contribute to the cooling observed in [8]. A different situation is the setup used in [7].…”

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confidence: 99%

“…Such a situation can be realized when an electrode has a strongly dependent density of states, or if the tunneling process takes place close to the top of a barrier. The first case is relevant to the experiments reported in [7], where one of the electrodes is made of graphite, and to the experiments presented in [8], where the electrodes are made of superconducting Al, and tunneling processes take place near the gap edges. Asymmetric I-V characteristics have also been reported in [10].…”

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confidence: 99%

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Nonequilibrium electronic distribution in single-electron devices

Garcı́a

Guinea

1998

Phys. Rev. B

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The electronic distribution in devices with sufficiently small dimensions may not be in thermal equilibrium with their surroundings. Systems where the occupancies of electronic states are solely determined by tunneling processes are analyzed. It is shown that the effective temperature of the device may be higher, or lower, than that of its environment, depending on the applied voltage and the energy dependence of the tunneling rates. The I-V characteristics become asymmetric. Comparison with recent experiments is made. 75.10.Jm, 75.10.Lp, 75.30.Ds. In small devices, the coupling between electrons and the lattice is suppressed. At sufficiently low temperatures, only long wavelength accoustical phonons are excited. If the electrons are localized in a region much smaller than the wavelength of the phonons, the interaction between the electrons and the phonons is significantly reduced [1]. As a result, the electron temperature may be different from that of the surrounding medium.Usually, the electron temperature in small devices tend to be higher than that of the environment, because of dissipation at the device [1] (see also [2]), via shake-up processes. This effect can explain a number of experiments [3,4].In the following, we analyze the electronic distribution in a small device, when it is controlled by the electronic exchange with the external leads. The general equations which describe the single level occupancies were first discussed in [6,5]. These authors considered mostly the inluence of a non negligible single level spacing in the I-V characteristics of semiconductor nanostructures. In these systems, the effects of the energy dependence of the transmission through the barrier, or of the density of states in the external leads is not important. We will generalize the previous work to situations where energy dependent tunneling rates also contribute to modify the electronic distribution. As it will be seen below, an energy dependent tunneling rate, T (ǫ), can modify significantly the electronic distribution in the central electrode of a single electron device, if T ′ (ǫ)/T (ǫ) is comparable to the inverse of the temperature at which the device is operated. Such a situation can be realized when an electrode has a strongly dependent density of states, or if the tunneling process takes place close to the top of a barrier. The first case is relevant to the experiments reported in [7], where one of the electrodes is made of graphite, and to the experiments presented in [8], where the electrodes are made of superconducting Al, and tunneling processes take place near the gap edges. Asymmetric I-V characteristics have also been reported in [10]. Some features of these experiments are also consistent with the work reported here.A particularly interesting case is presented in [7]. The observed Coulomb staircase can only be fitted by the orthodox theory [11][12][13], if an effective temperature of ∼ 170K is assumed, although the experiment is performed at room temperature. A large temperature difference between the...

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“…It may be noted that many cryogenic ballistic refrigerators such as normal-insulating-semiconductor ͑NIS͒ junction devices [32][33][34] and quantum dot refrigerators 35 utilize either two-or one-dimensional reservoirs where the difference between k x and k r filtered devices is less dramatic or nonexistent.…”

Section: ͑7͒mentioning

confidence: 99%

Electronic efficiency in nanostructured thermionic and thermoelectric devices

et al. 2005

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Advances in solid-state device design now allow the spectrum of transmitted electrons in thermionic and thermoelectric devices to be engineered in ways that were not previously possible. Here we show that the shape of the electron energy spectrum in these devices has a significant impact on their performance. We distinguish between traditional thermionic devices where electron momentum is filtered in the direction of transport only and a second type, in which the electron filtering occurs according to total electron momentum. Such "total momentum filtered" thermionic devices could potentially be implemented in, for example, quantum dot superlattices. It is shown that whilst total momentum filtered thermionic devices may achieve an efficiency equal to the Carnot value, traditional thermionic devices are limited to an efficiency below this. Our second main result is that the electronic efficiency of a device is not only improved by reducing the width of the transmission filter as has previously been shown, but also strongly depends on whether the transmission probability rises sharply from zero to full transmission. The benefit of increasing efficiency through a sharply rising transmission probability is that it can be achieved without sacrificing device power, in contrast to the use of a narrow transmission filter which can greatly reduce power. We show that devices that have a sharply rising transmission probability significantly outperform those that do not and that such transmission probabilities may be achieved with practical single and multibarrier devices. We discuss how the shape of the electron energy spectrum will also have an effect on the electronic efficiency of thermoelectric devices due to mathematical equivalences in the ballistic and diffusive formalisms. Finally, we present an experimental measure that might be used to provide an indication of the nature of the electron energy spectrum and the electronic efficiency of a ballistic device.

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Electronic microrefrigerator based on a normal-insulator-superconductor tunnel junction

Cited by 303 publications

References 10 publications

Magnetic-field-induced stabilization of nonequilibrium superconductivity in a normal-metal/insulator/superconductor junction

Magnetic-field-induced stabilization of nonequilibrium superconductivity in a normal-metal/insulator/superconductor junction

Nonequilibrium electronic distribution in single-electron devices

Electronic efficiency in nanostructured thermionic and thermoelectric devices

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