Distribution of Supercurrent Switching in Graphene under the Proximity Effect

Coskun, Ulas; Brenner, Matthew; Hymel, T.; Vakaryuk, Victor; Levchenko, Alex; Bezryadin, Alexey

doi:10.1103/physrevlett.108.097003

Cited by 51 publications

(65 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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 critical current I C on gate voltage V G (Figure 1c The critical current I C is observed to rapidly decrease with temperature, however the functional form of I C (T ) strongly depends on the length of the junction.…”

mentioning

confidence: 99%

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

et al. 2016

View full text Add to dashboard Cite

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...

show abstract

mentioning

confidence: 99%

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

et al. 2016

View full text Add to dashboard Cite

show abstract

“…The distribution of switching current probability P γsw (n/N ) is the quantity that can be promptly compared with experiments [1,[3][4][5][6][7] and it reproduces the qualitative features of macroscopic quantum tunnel in JJ: the appearance of a peak, or a most probable switching current when the potential energy is comparable to the quantum fluctuations [13]. For a detailed comparison with tunnel theory we consider the WKB approximation for the normalized rate Γ:…”

Section: B Switching Current Probability Distributionmentioning

confidence: 97%

“…Josephson Junctions (JJ) are a well established playground for macroscopic quantum tunneling [1][2][3][4][5][6][7] and a prominent field where the basic concepts of quantum mechanics have been successfully demonstrated in a mesoscopic system, with potential technological implications in quantum computing [8]. The subject is of interest per se as an application quantum dynamics to a macroscopic object (analogous, for example, to the particle-like dynamics of fluxons described by collective coordinates [2] or to the motion of the end masses of advanced gravitational wave detectors working near the quantum limit [9]) and to validate non ideal quantum measurements models [10].…”

Section: Introductionmentioning

confidence: 99%

“…In fact one could conceive that the environment noise enters the system bearing an effective temperature that is higher than the thermodynamic temperature. When escapes can be ascribed to stochastic activation, it is difficult to discern between thermal activation [15,16] and quantum tunnel [1,[3][4][5][6][7], inasmuch several quantum effects, as resonance with level quantization [17] and Rabi oscillations [18], have been reproduced in classical activated JJ. It is therefore important to pinpoint effects that are unique for quantum systems, and could not possibly be confused with classical analogue.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Nonideal quantum measurement effects on the switching-current distribution of Josephson junctions

Pierro

Филатрелла

2016

Phys. Rev. A

View full text Add to dashboard Cite

The quantum character of Josephson junctions is ordinarily revealed through the analysis of the switching currents, i.e. the current at which a finite voltage appears: A sharp rise of the voltage signals the passage (tunnel) from a trapped state (the zero voltage solution) to a running state (the finite voltage solution). In this context, we investigate the probability distribution of the Josephson junctions switching current taking into account the effect of the bias sweeping rate and introducing a simple nonideal quantum measurements scheme. The measurements are modelled as repeated voltage samplings at discrete time intervals, that is with repeated projections of the time dependent quantum solutions on the static or the running states, to retrieve the probability distribution of the switching currents. The distribution appears to be immune of the quantum Zeno effect, and it is close to, but distinguishable from, the Wentzel-Kramers-Brillouin approximation. For energy barriers comparable to the quantum fundamental energy state and in the fast bias current ramp rate the difference is neat, and remains sizeable in the asymptotic slow rate limit. This behaviour is a consequence of the quantum character of the system that confirms the presence of a backreaction of quantum measurements on the outcome of mesoscopic Josephson junctions.

show abstract

“…Experimental evidence of superconducting states in graphene, with coherent propagation of Cooper pairs, has been recently found [99][100][101]. Moreover, noise effects in the dynamical behavior of graphene JJs have been analyzed from experimental and theoretical point of view [97,100,[102][103][104]. In this section we study the transient dynamics of an underdamped superconductor−graphene−superconductor (SGS) junction, as the simultaneous action of an external driving force, oscillating with frequency ω, and a stochastic signal, which represents a random force of intensity γ, is taken into account.…”

Section: Short and Long Jjmentioning

confidence: 99%

Nonlinear Relaxation Phenomena in Metastable Condensed Matter Systems

Spagnolo

Guarcello

Magazzù

et al. 2016

Entropy

100

View full text Add to dashboard Cite

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

show abstract

Distribution of Supercurrent Switching in Graphene under the Proximity Effect

Cited by 51 publications

References 30 publications

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

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

Nonideal quantum measurement effects on the switching-current distribution of Josephson junctions

Nonlinear Relaxation Phenomena in Metastable Condensed Matter Systems

Contact Info

Product

Resources

About