Josephson current in ballistic superconductor-graphene systems

Hagymási, Imre; Kormányos, Andor; Cserti, József

doi:10.1103/physrevb.82.134516

Cited by 51 publications

(58 citation statements)

References 49 publications

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“…In this low-density regime at the close vicinity of the Dirac point, lower temperatures is required to accurately measured supercurrent. Compared with the theoretical predictions on ideal-wide ballistic Josephson weak links 2,9 , where I c R N $ 2:44 D e , the value of the I c R N product obtained from our measurements, $ 1 3 D e , is much smaller. Such discrepancy may be attributed to the imperfect graphene-superconductor interface, and the relatively high-measurement temperature.…”

Section: Discussionmentioning

confidence: 89%

“…In a current driven Josephson weak link, the RCSJ can be described by equation: 2 , where I is the driving current, f the phase difference between the two superconducting contacts, R the normal state resistance, C the junction capacitance and I c the intrinsic Josephson current. Here we used the approximation that the current-phase relation is sinusoidal, while in the actual devices the current-phase relation is skewed 9,25,26 . Such sinusoidal ARTICLE approximation is justified since the error is smaller than B5% (see Supplementary Note 3).…”

Section: Resultsmentioning

confidence: 99%

“…From the practical point of view, the high mobility of the charge carriers in graphene allows a decent magnitude of supercurrent in the superconducting weak links. The tunability of the supercurrent through electric field gating suggests the potential applications in the graphene-superconductor devices [6][7][8][9] .…”

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confidence: 99%

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Ballistic-like supercurrent in suspended graphene Josephson weak links

Mizuno

Nielsen

2013

Nat Commun

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The interplay of the massless Dirac fermions in graphene and the Cooper pair states in a superconductor has the potential to give rise to exotic physical phenomena and useful device applications. But to date, the junctions formed between graphene and superconductors on conventional substrates have been highly disordered. Charge scattering and potential fluctuations caused by such disorder are believed to have prevented the emergence or observation of new physics. Here we propose to address this problem by forming suspended graphene-superconductor junctions. We demonstrate the fabrication of high-quality suspended monolayer graphene-NbN Josephson junctions with device mobility in excess of 150,000 cm 2 per Vs, minimum carrier density below 10 10 cm À 2 , and the flow of a supercurrent at critical temperatures greater than 2 K. The characteristics of our Josephson junctions are consistent with ballistic transport, with a linear dependence on the Fermi energy that reflects of linear dispersion of massless Dirac fermions.

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Section: Discussionmentioning

confidence: 89%

Section: Resultsmentioning

confidence: 99%

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Ballistic-like supercurrent in suspended graphene Josephson weak links

Mizuno

Nielsen

2013

Nat Commun

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“…Moreover, at higher temperatures the superconducting gap will be suppressed; we approximate the temperature dependence of the gap as ∆(T ) ≈ ∆ 0 1 − ( T T C ) 2 , where ∆ 0 is the gap for T → 0, and T C is the critical temperature [8,29,30]. Taking the complete temperaturedependent expression, we fit I C (T ) for Junction A using the value ∆ 0 = 1.2 meV extracted from multiple Andreev reflections measurements.…”

Section: Oct 2016mentioning

confidence: 99%

“…[29]). In our case, ξ ≈ 550 nm, which explains the suppressed δE in the intermediate regime (Junctions B, E).…”

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confidence: 99%

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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Experimental Evidence for the Existence of Interfaces in Graphite and Their Relation to the Observed Metallic and Superconducting Behavior

Esquinazi

Lysogorskiy

2016

Basic Physics of Functionalized Graphite

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Josephson current in ballistic superconductor-graphene systems

Cited by 51 publications

References 49 publications

Ballistic-like supercurrent in suspended graphene Josephson weak links

Ballistic-like supercurrent in suspended graphene Josephson weak links

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

Experimental Evidence for the Existence of Interfaces in Graphite and Their Relation to the Observed Metallic and Superconducting Behavior

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