Pb–Graphene–Pb Josephson Junctions: Characterization in Magnetic Field

Borzenets, Ivan; Coskun, Ulas; Mebrahtu, Henok; Finkelstein, Gleb

doi:10.1109/tasc.2012.2198472

Cited by 11 publications

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References 14 publications

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“…The two longest junctions (junctions 4 and 5) never developed a supercurrent. These values are suppressed compared to the naive estimates of the critical current I C ∼ ∆/R N e (R N is the normal resistance of the junction) most likely due to disorder, as discussed in our earlier publication 13 .…”

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confidence: 80%

Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures

et al. 2013

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We examine the nature of the transitions between the normal and superconducting branches in superconductor-graphene-superconductor Josephson junctions. We attribute the hysteresis between the switching (superconducting to normal) and retrapping (normal to superconducting) transitions to electron overheating. In particular, we demonstrate that the retrapping current corresponds to the critical current at an elevated temperature, where the heating is caused by the retrapping current itself. The superconducting gap in the leads suppresses the hot electron outflow, allowing us to further study electron thermalization by phonons at low temperatures (T≲1 K). The relationship between the applied power and the electron temperature was found to be P∝T3, which we argue is consistent with cooling due to electron-phonon interactions.

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Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures

et al. 2013

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“…To our knowledge Pb has not been used previously in InAs or any NW Josephson junctions, though a dilute PbIn compound and Pb have proved to be a suitable candidates for Josephson junctions using graphene as a weak link [19,20]. The high critical temperature of Pb combined with the ease of evaporation makes it a promising and solid alternative to superconducting Nb as a contact electrode material.…”

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Pb/InAs Nanowire Josephson Junction with High Critical Current and Magnetic Flux Focusing

et al. 2015

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We have studied mesoscopic Josephson junctions formed by highly n-doped InAs nanowires and superconducting Ti/Pb source and drain leads. The current-voltage properties of the system are investigated by varying temperature and external out-of-plane magnetic field. Superconductivity in the Pb electrodes persists up to ∼ 7 K and with magnetic field values up to 0.4 T. Josephson coupling at zero backgate voltage is observed up to 4.5 K and the critical current is measured to be as high as 615 nA. The supercurrent suppression as a function of the magnetic field reveals a diffraction pattern that is explained by a strong magnetic flux focusing provided by the superconducting electrodes forming the junction.

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“…Device dimensions are listed in the supplementary information [16]. [1,[17][18][19][20][21], which could be attributed to either underdamped junction dynamics [8,20], or to the self-heating by the retrapping current [1,23]. As discussed in the supplementary material, the second scenario is more likely for most of the range studied here.…”

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Ballistic Graphene Josephson Junctions from the Short to the Long Junction Regimes

et al. 2016

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We investigate the critical current, I C , of ballistic Josephson junctions made of encapsulated graphene/boron-nitride heterostructures. We observe a crossover from the short to the long junction regimes as the length of the device increases. In long ballistic junctions, I C is found to scale as ∝ exp(−k B T /δE). The extracted energies δE are independent of the carrier density and proportional to the level spacing of the ballistic cavity, as determined from Fabry-Perot oscillations of the junction normal resistance. As T → 0 the critical current of a long (or short) junction saturates at al level determined by the product of δE (or ∆) and the number of the junction's transversal modes.1 arXiv:1604.07320v3 [cond-mat.mes-hall] Oct 2016Encapsulated graphene/boron-nitride heterostructures emerged in the past year as a medium of choice for studying proximity-induced superconductivity in the ultra-clean limit [1][2][3][4]. These junctions support the ballistic propagation of superconducting currents across micron-scale graphene channels, and their critical current is gate-tunable across several orders of magnitude. In these devices, a rich phenomenology arises from the interplay of superconductivity with ballistic transport [1], cyclotron motion [2], and even the quantum Hall effect at high magnetic field [4]. In a superconductor -normal metal -superconductor (SNS) junction, single particles in the N region cannot enter the superconductor and therefore experience Andreev reflections at each S-N interface. This results in Andreev bound states (ABS), which are capable of 2 carrying superconducting current across the N region. In long ballistic junctions, the energy spectrum of the ABS is quantized with a level spacing of T is independent of V G . In the case of long ballistic graphene junctions, the inverse slope δE is expected to be independent of the carrier density and inversely proportional to L.In this work we study several ballistic junctions of different length and demonstrate that the temperature dependence of the critical current dramatically differs in the long and short regimes. For long junctions, we observe an exponential scaling of the current through the [5, 6,10,11]. Note that in graphene v F is a constant, and δE is expected to be independent of the carrier density or the mobility , 17-21], which could be attributed to either underdamped junction dynamics [8,20], or to the self-heating by the retrapping current [1,23]. As discussed in the supplementary material, the second scenario is more likely for most of the range studied here. Based on the measurements of the switching statistics [16,[24][25][26], in the following we will use the switching current to represent the true critical current of the junction, I C .In the hole-doped regime, the reflections of ballistic charge carriers from the n-doped contact interfaces yield the quantum ("Fabry-Perot") interference. A very similar oscillation pattern could be observed in the dependence of both the the normal conductance, G N , and the critica...

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Pb–Graphene–Pb Josephson Junctions: Characterization in Magnetic Field

Cited by 11 publications

References 14 publications

Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures

Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures

Pb/InAs Nanowire Josephson Junction with High Critical Current and Magnetic Flux Focusing

Ballistic Graphene Josephson Junctions from the Short to the Long Junction Regimes

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