Complete gate control of supercurrent in graphene p–n junctions

Choi, Jaehyun; Lee, Gil‐Ho; Park, Sunghun; Jeong, Dongchan; Lee, Jun Young; Sim, Hyun Sub; Doh, Yong-Joo; Lee, Hu-Jong

doi:10.1038/ncomms3525

Cited by 68 publications

(47 citation statements)

References 55 publications

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“…Recent advancement of fabrication methods for nanoscale devices enables us to explore various quantum electronic transport phenomena in nano-hybrid mesoscopic systems combined with superconductivity [2][3][4][5][6][7][8]. Usually aluminum (Al) is used as a superconducting electrode because of its very long superconducting coherence length,  Al ~ 1.6 m.…”

Section: Introductionmentioning

confidence: 99%

Fabrication and characterization of PbIn-Au-PbIn superconducting junctions

Kim¹,

Kim²,

Kim³

et al. 2016

Progress in Superconductivity and Cryogenics

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We report on the fabrication and measurement results of the electrical transport properties of superconductor-normal metalsuperconductor (SNS) weak links, made of PbIn superconductor and Au metal. The maximum supercurrent reaches up to ~ 6 A at T = 2.3 K and the supercurrent persists even at T = 4.7 K. Magnetic field dependence of the critical current is consistent with a theoretical fit using the narrow junction model. The superconducting quantum interference device (SQUID) was also fabricated using two PbIn-Au-PbIn junctions connected in parallel. Under perpendicular magnetic field, we clearly observed periodic oscillations of dV/dI with a period of magnetic flux quantum threading into the supercurrent loop of the SQUID. Our fabrication methods would provide an easy and simple way to explore the superconducting proximity effects without ultra-low-temperature cryostats.

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Section: Introductionmentioning

confidence: 99%

Fabrication and characterization of PbIn-Au-PbIn superconducting junctions

Kim¹,

Kim²,

Kim³

et al. 2016

Progress in Superconductivity and Cryogenics

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“…These properties combined with the possibility to electrostatically control the carrier density n offer tunable Josephson junctions in a regime that can be referred to as ballistic proximity superconductivity 21 . Despite intense interest in SGS devices [3][4][5][6][7][8][9][10][11][12][13][14][15][16] that can show features qualitatively different from the conventional SNS behaviour 2,3 , ballistic graphene Josephson junctions 15,16 remain little studied. Our SGS devices are schematically shown in Fig.…”

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confidence: 99%

“…

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mentioning

confidence: 99%

Quantum oscillations of the critical current and high-field superconducting proximity in ballistic graphene

Shalom¹,

Zhu²,

Fal’ko³

et al. 2015

Nature Phys

224

253

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Graphene-based Josephson junctions provide a novel platform for studying the proximity e ect [1][2][3] due to graphene's unique electronic spectrum and the possibility to tune junction properties by gate voltage [4][5][6][7][8][9][10][11][12][13][14][15][16] . Here we describe graphene junctions with a mean free path of several micrometres, low contact resistance and large supercurrents. Such devices exhibit pronounced Fabry-Pérot oscillations not only in the normal-state resistance but also in the critical current. The proximity e ect is mostly suppressed in magnetic fields below 10 mT, showing the conventional Fraunhofer pattern. Unexpectedly, some proximity survives even in fields higher than 1 T. Superconducting states randomly appear and disappear as a function of field and carrier concentration, and each of them exhibits a supercurrent carrying capacity close to the universal quantum limit 17,18 . We attribute the high-field Josephson e ect to mesoscopic Andreev states that persist near graphene edges. Our work reveals new proximity regimes that can be controlled by quantum confinement and cyclotron motion.The superconducting proximity effect relies on penetration of Cooper pairs from a superconductor (S) into a normal metal (N) and is most pronounced in systems with transparent SN interfaces and weak scattering, where superconducting correlations penetrate deep inside the normal metal. Despite being one atom thick and having a low density of states, which vanishes at the Dirac point, graphene (G) can exhibit low contact resistance and ballistic transport on a micrometre scale 19,20 exceeding the distance between the superconducting leads by an order of magnitude. These properties combined with the possibility to electrostatically control the carrier density n offer tunable Josephson junctions in a regime that can be referred to as ballistic proximity superconductivity 21 . Despite intense interest in SGS devices 3-16 that can show features qualitatively different from the conventional SNS behaviour 2,3 , ballistic graphene Josephson junctions 15,16 remain little studied. Our SGS devices are schematically shown in Fig. 1 and described in further detail in Supplementary Section 1. The essential technological difference from the previously studied SGS junctions 4-14 is the use of graphene encapsulated between boron nitride crystals 19,20 as well as a new nanostrip geometry of the contacts. This allows high carrier mobility, low charge inhomogeneity and low contact resistance. More than twenty SGS junctions with a width W between 3 and 8 µm and a length L between 0.15 and 2.5 µm were studied, all exhibiting a finite supercurrent at low temperatures (T ), reproducible behaviour and consistent changes with L and W . First, we characterize the devices above the transition temperature T C ≈ 7 K of our superconducting contacts. Figure 1b shows examples of the normal-state resistance R n as a function of back gate voltage V g that changes n in graphene. The neutrality point (NP) was found to be shifted to negative ...

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“…• Short Graphene JJ Recently, Josephson devices with a graphene sheet as interlayer has attracted an increasing scientific interest [97,98]. Experimental evidence of superconducting states in graphene, with coherent propagation of Cooper pairs, has been recently found [99][100][101].…”

Section: Short and Long Jjmentioning

confidence: 99%

Nonlinear Relaxation Phenomena in Metastable Condensed Matter Systems

Spagnolo

Guarcello

Magazzù

et al. 2016

Entropy

100

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Nonlinear relaxation phenomena in three different systems of condensed matter are investigated. (i) First, the phase dynamics in Josephson junctions is analyzed. Specifically, a superconductor-graphene-superconductor (SGS) system exhibits quantum metastable states, and the average escape time from these metastable states in the presence of Gaussian and correlated fluctuations is calculated, accounting for variations in the the noise source intensity and the bias frequency. Moreover, the transient dynamics of a long-overlap Josephson junction (JJ) subject to thermal fluctuations and non-Gaussian noise sources is investigated. Noise induced phenomena are observed, such as the noise enhanced stability and the stochastic resonant activation. (ii) Second, the electron spin relaxation process in a n-type GaAs bulk driven by a fluctuating electric field is investigated. In particular, by using a Monte Carlo approach, we study the influence of a random telegraph noise on the spin polarized transport. Our findings show the possibility to raise the spin relaxation length by increasing the amplitude of the external fluctuations. Moreover, we find that, crucially, depending on the value of the external field strength, the electron spin depolarization length versus the noise correlation time increases up to a plateau. (iii) Finally, the stabilization of quantum metastable states by dissipation is presented. Normally, quantum fluctuations enhance the escape from metastable states in the presence of dissipation. We show that dissipation can enhance the stability of a quantum metastable system, consisting of a particle moving in a strongly asymmetric double well potential, interacting with a thermal bath. We find that the escape time from the metastable region has a nonmonotonic behavior versus the system-bath coupling and the temperature, producing a stabilizing effect.Keywords: metastability; nonequilibrium statistical mechanics and nonlinear relaxation time; noise enhanced stability; Josephson junction; spin polarized transport in semiconductors; open quantum systems; quantum noise enhanced stability

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Complete gate control of supercurrent in graphene p–n junctions

Cited by 68 publications

References 55 publications

Fabrication and characterization of PbIn-Au-PbIn superconducting junctions

Fabrication and characterization of PbIn-Au-PbIn superconducting junctions

Quantum oscillations of the critical current and high-field superconducting proximity in ballistic graphene

Nonlinear Relaxation Phenomena in Metastable Condensed Matter Systems

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