Direct Observation of the Transition from the Conventional Superconducting State to the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>π</mml:mi></mml:math>State in a Controllable Josephson Junction

Baselmans, J. J. A.; Heikkilä, Tero T.; Wees, J.B. van; Klapwijk, T. M.

doi:10.1103/physrevlett.89.207002

Cited by 60 publications

(61 citation statements)

References 23 publications

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“…Such a fine structure of the Josephson current inversion has been observed experimentally in long SNS junctions. 11 At very large interface resistance, γ ≫ 1, this fine structure becomes irresolvable because of in this limit the phase dependence in I s (E, φ) for relevant energies is given by a prefactor sin φ, and therefore the compensation effect appears simultaneously at all phases. 17 …”

Section: Nonequilibrium Josephson Currentmentioning

confidence: 99%

“…10,11,12 The non-equilibrium Josephson effect has been first predicted 4 and then theoretically studied in the ballistic junctions. 2,13,14,15 Non-equilibrium population of the Andreev states 16 induced by the current injection leads to a full-scale variation of the Josephson current with the applied voltage and to the inversion of the current direction.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, in contrast to weak proximity regime, 17 the current reversion exhibits a fine structure similar to the one theoretically discussed for ballistic junctions, 15 and recently demonstrated in the experiment with long diffusive junctions. 11 The interplay of the injected and Josephson currents in the strong proximity regime is important for the interpretation of experiments with current biased junctions, Fig. 1(c).…”

Section: Introductionmentioning

confidence: 99%

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Nonequilibrium Josephson effect in short-arm diffusive SNS interferometers

2003

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We study non-equilibrium Josephson effect and phase-dependent conductance in three-terminal diffusive interferometers with short arms. We consider strong proximity effect and investigate an interplay of dissipative and Josephson currents co-existing within the same proximity region. In junctions with transparent interfaces, the suppression of the Josephson current appears at rather large voltage, eV ∼ ∆, and the current vanishes at eV ≥ ∆. Josephson current inversion becomes possible in junctions with resistive interfaces, where it occurs within a finite interval of the applied voltage. Due to the presence of considerably large and phase-dependent injection current, the critical current measured in a current biased junction does not coincide with the maximum Josephson current, and remains finite when the true Josephson current is suppressed. The voltage dependence of the conductance shows two pronounced peaks, at the bulk gap energy, and at the proximity gap energy; the phase oscillation of the conductance exhibits qualitatively different form at small voltage eV < ∆, and at large voltage eV > ∆.

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Section: Nonequilibrium Josephson Currentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nonequilibrium Josephson effect in short-arm diffusive SNS interferometers

2003

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“…This quantity makes evident the link between Andreev physics and the Josephson effect. It has seldom been discussed in the literature 8,[34][35][36][37] and, to the best of our knowledge, has never been directly connected to the DOS. We propose here the heuristic definition J S (E, ϕ) = −(1/φ 0 ) E 0 (∂DOS/∂ϕ) ( , ϕ) d , which can easily be checked as being correct in the case of a set of discrete ABS.…”

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confidence: 99%

Tunnelling spectroscopy of Andreev states in graphene

et al. 2017

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A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties 1,2 . This proximity e ect microscopically originates from the formation in the conductor of entangled electron-hole states, called Andreev states [3][4][5][6][7][8] . Spectroscopic studies of Andreev states have been performed in just a handful of systems 9-13 . The unique geometry, electronic structure and high mobility of graphene 14,15 make it a novel platform for studying Andreev physics in two dimensions. Here we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity e ect in superconductor-graphenesuperconductor junctions. The measured energy spectra, which depend on the phase di erence between the superconductors, reveal the presence of a continuum of Andreev bound states. Moreover, our device heterostructure geometry and materials enable us to measure the Andreev spectrum as a function of the graphene Fermi energy, showing a transition between di erent mesoscopic regimes. Furthermore, by experimentally introducing a novel concept, the supercurrent spectral density, we determine the supercurrent-phase relation in a tunnelling experiment, thus establishing the connection between Andreev physics at finite energy and the Josephson e ect. This work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials [16][17][18] .When a normal quantum conductor (N) is sandwiched between two superconductors (S), a current can flow in the absence of any voltage, due to the Josephson effect 1 . This macroscopic supercurrent is driven by the difference between the order parameter phases of the two superconductors, ϕ. Microscopically, it corresponds to the coherent flow of Cooper pairs through the conductor, which is made possible by successive Andreev reflections at the N/S interfaces, where electrons (holes) are reflected as oppositespin holes (electrons) (Fig. 1a). Due to this process, resonant electron-hole states form in the central conductor, known as Andreev bound states (ABS) 3-6 . They lie as energy levels inside the superconducting gap [−∆, ∆], only negative-energy states being populated in the ground state (Fig. 1b). Crucially, the Andreev energy E n (ϕ) depends on ϕ, and each populated ABS carries in response a supercurrent (1/φ 0 )(∂E n /∂ϕ), where φ 0 = /2e is the reduced flux quantum, with the reduced Planck constant and e the elementary charge. The overall phase-dependent Andreev spectrum is shown in Fig. 1c and depends on geometric and microscopic parameters 7,8 , such as the conductor dimensions that determine the number of ABS, the scattering processes in the conductor and the contact's transparency. Strong ABS phase dependence, and therefore a prominent proximity effect, is achieved in ballistic systems with transparent N/S interfaces 7,8 .Graphene (G) can exhibit low contact resistance and weak scattering when connected to superconducting electrodes 19,20 . These properties, combined with t...

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“…Under certain conditions, the CPR of the junction͑s͒ is not a simple sine, but it can contain higher harmonics: I s ͑ ͒ = ͚ n I c ͑n͒ sin n , where the coupling coefficients I c ͑n͒ quantify the relative strength of processes with a coherent transfer of n Cooper pairs. 1 In some cases, the first order coefficient I c ͑1͒ can even vanish, for instance, in asymmetric 45°grain boundary junctions in d-wave symmetry superconductors, 2,3 in out of equilibrium superconductornormal-metal-superconductor junctions 4 and for ballistic superconductor-ferromagnet-superconductor ͑SFS͒ junctions at the 0-transition. 5,6 The remaining second order coefficient I c ͑2͒ will result in a doubling of the frequency in the interference pattern.…”

Section: Introductionmentioning

confidence: 99%

Bistability in superconducting rings containing an inhomogeneous Josephson junction

et al. 2008

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We investigate the magnetic response of a superconducting Nb ring containing a ferromagnetic PdNi Josephson junction and a tunnel junction in parallel. Doubling of the switching frequency is observed within certain intervals of the external magnetic field. For sinusoidal current-phase relations in both junctions, our model of a double superconducting quantum interference device ͑a small two-junction loop that interrupts the larger ring͒ explains this feature by a sequence of current reversals in the ferromagnetic section of the junction in these field intervals. The switching anomalies are induced by the coupling between the magnetic fluxes in the two superconducting loops.

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Direct Observation of the Transition from the Conventional Superconducting State to theπState in a Controllable Josephson Junction

Cited by 60 publications

References 23 publications

Nonequilibrium Josephson effect in short-arm diffusive SNS interferometers

Nonequilibrium Josephson effect in short-arm diffusive SNS interferometers

Tunnelling spectroscopy of Andreev states in graphene

Bistability in superconducting rings containing an inhomogeneous Josephson junction

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