Trapping of quasiparticles of a nonequilibrium superconductor

Pekola, Jukka P.; Anghel, Dragos-Victor; Suppula, Tarmo; Suoknuuti, J. K.; Manninen, A. J.; Manninen, M.

doi:10.1063/1.126474

Cited by 74 publications

(77 citation statements)

References 10 publications

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“…In this configuration, a reduction of the electron temperature from 300 to about 100 mK was obtained. Later on, other experimental evidence of electron cooling in SINIS metallic structures was reported ͑Fisher et Leoni et al, 1999Leoni et al, , 2003Vystavkin et al, 1999;Arutyunov et al, 2000;Luukanen et al, 2000;Pekola, Anghel, et al, 2000;Tarasov et al, 2003;Clark et al, 2004;Pekola, Heikkilä, et al, 2004͒. In these experiments NIS junc- FIG. 26.…”

Section: "Si…nis Structuresmentioning

confidence: 95%

“…28͑a͔͒. Such traps act as sinks of quasiparticles absorbing almost all the excess quasiparticle energy present in the superconductor and have proved to be efficient in heat removal from the superconductor leading to improvement of SINIS device cooling performance ͑Luukanen et al, 2000; Pekola, Anghel, et al, 2000;Pekola, Heikkilä, et al, 2004͒. All these are commonly exploited tricks for the thermalization of superconducting electrodes, and it is a reasonable approximation to set T e,S = T ph .…”

Section: "Si…nis Structuresmentioning

confidence: 99%

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Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications

et al. 2006

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This review presents an overview of the thermal properties of mesoscopic structures. The discussion is based on the concept of electron energy distribution, and, in particular, on controlling and probing it. The temperature of an electron gas is determined by this distribution: refrigeration is equivalent to narrowing it, and thermometry is probing its convolution with a function characterizing the measuring device. Temperature exists, strictly speaking, only in quasiequilibrium in which the distribution follows the Fermi-Dirac form. Interesting nonequilibrium deviations can occur due to slow relaxation rates of the electrons, e.g., among themselves or with lattice phonons. Observation and applications of nonequilibrium phenomena are also discussed. The focus in this paper is at low temperatures, primarily below 4 K, where physical phenomena on mesoscopic scales and hybrid combinations of various types of materials, e.g., superconductors, normal metals, insulators, and doped semiconductors, open up a rich variety of device concepts. This review starts with an introduction to theoretical concepts and experimental results on thermal properties of mesoscopic structures. Then thermometry and refrigeration are examined with an emphasis on experiments. An immediate application of solid-state refrigeration and thermometry is in ultrasensitive radiation detection, which is discussed in depth. This review concludes with a summary of pertinent fabrication methods of presented devices.

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Section: "Si…nis Structuresmentioning

confidence: 95%

Section: "Si…nis Structuresmentioning

confidence: 99%

Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications

et al. 2006

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“…The excess QP density close to the junction can be diminished by ©2011 American Physical Society fabricating very thick S electrodes, 16 or covering them partially by a layer of normal metal that acts as a QP trap. [18][19][20] The QP population is typically modeled in terms of a diffusion equation, describing their recombination retarded by phonon retrapping, and other loss mechanisms. [21][22][23][24][25] Converting the excess density into an effective, position-dependent temperature T (x), one finds 26,27 that at phonon temperatures k B T the S leads can be overheated on a length scale ranging from tens of micrometers to a millimeter, as the electron-phonon relaxation and electronic heat conduction are exponentially suppressed compared to their normal-state values.…”

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confidence: 99%

“…In addition, Cu replicas of the Al leads form large-area tunnel junctions by partly covering the Al layer, serving as QP traps, albeit of suboptimal performance. 19 The island electron temperature T N is measured by biasing the probe junctions by a constant current I th , and measuring the voltage drop V th , calibrated against T 0 at V = 0. The solid lines in Fig.…”

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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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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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“…These approaches include engineering the spatial profile of the superconducting gap to steer quasiparticles away from Josephson junctions [7,8], and cooling down a device in a magnetic field in order to generate vortices that trap quasiparticles in their cores [9][10][11]. Here, we consider a different way to capture quasiparticles using normal-metal traps, a proposal which has been implemented in single-electron turnstiles [12], hybrid multilayer coolers [13,14], superconducting resonators [15], and qubits [16].…”

Section: Introductionmentioning

confidence: 99%

Proximity effect in normal-metal quasiparticle traps

Hosseinkhani

Catelani

2018

Phys. Rev. B

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In many superconducting devices, including qubits, quasiparticle excitations are detrimental. A normal metal (N ) in contact with a superconductor (S) can trap these excitations; therefore, such a trap can potentially improve the device's performances. The two materials influence each other, a phenomenon known as proximity effect which has drawn attention since the 1960's. Here, we study whether this mutual influence places a limitation on the possible performance improvement in superconducting qubits. We first revisit the proximity effect in uniform NS bilayers; we show that the density of states is of the Dynes type above the minigap. We then extend our results to describe a nonuniform system in the vicinity of a trap edge. Using these results together with a phenomenological model for the suppression of the quasiparticle density due to the trap, we find in a transmon qubit an optimum trap-junction distance at which the qubit relaxation rate is minimized. This optimum distance, of the order of 4 to 20 coherence lengths, originates from the competition between proximity effect and quasiparticle density suppression. We conclude that the harmful influence of the proximity effect can be avoided so long as the trap is farther away from the junction than this optimum.

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Trapping of quasiparticles of a nonequilibrium superconductor

Cited by 74 publications

References 10 publications

Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications

Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications

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

Proximity effect in normal-metal quasiparticle traps

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