Phase Sensitive Experiments in Ferromagnetic-Based Josephson Junctions

Guichard, Wiebke; Aprili, M.; Bourgeois, Olivier; Kontos, Takis; Lesueur, J.; Gandit, P.

doi:10.1103/physrevlett.90.167001

Cited by 115 publications

(108 citation statements)

References 18 publications

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“…For our purposes it is important that in S/F bilayers there is a mesoscopic analogue of the LOFF-state. This phenomenon was predicted theoretically [15,16] and observed experimentally [17][18][19][20][21]. In this state Cooper pair acquires the total momentum 2Q or −2Q inside the ferromagnet as a response to the energy difference between the two spin directions.…”

supporting

confidence: 53%

Recovering of superconductivity in S/F bilayers under spin-dependent nonequilibrium quasiparticle distribution

Bobkova

Bobkov

2015

Jetp Lett.

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We study theoretically the influence of spin accumulation on superconductivity in a superconductor/ferromagnet bilayer. It is well-known that the superconductivity in S/F bilayers is suppressed by the proximity to a ferromagnet. The spin accumulation by itself is also a depairing factor. But here we show that creation of the spin accumulation on top of effective exchange depairing, caused by the proximity to a ferromagnet, can lead to an opposite result. The superconductivity can be partially recovered by spin-dependent quasiparticle distribution. The systems with realistic parameters are considered and the possible experimental setup is proposed.

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supporting

confidence: 53%

Recovering of superconductivity in S/F bilayers under spin-dependent nonequilibrium quasiparticle distribution

Bobkova

Bobkov

2015

Jetp Lett.

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“…as in, e.g., PdNi alloys with small Ni concentration [95]. Such conditions do not hold for ferromagnetic conductors like Fe, Co, Ni and its alloys, however.…”

Section: B Boundary Conditionsmentioning

confidence: 99%

“…The current through the contact between reservoir 1 (2) and the node is obtained by inserting the resulting distribution for the normal node into Eq. (95).…”

Section: E Spin-flip Transistormentioning

confidence: 99%

Non-collinear magnetoelectronics

2006

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The electron transport properties of hybrid ferromagnetic|normal metal structures such as multilayers and spin valves depend on the relative orientation of the magnetization direction of the ferromagnetic elements. Whereas the contrast in the resistance for parallel and antiparallel magnetizations, the so-called Giant Magnetoresistance, is relatively well understood for quite some time, a coherent picture for non-collinear magnetoelectronic circuits and devices has evolved only recently. We review here such a theory for electron charge and spin transport with general magnetization directions that is based on the semiclassical concept of a vector spin accumulation. In conjunction with first-principles calculations of scattering matrices many phenomena, e.g. the currentinduced spin-transfer torque, can be understood and predicted quantitatively for different material combinations.

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“…An evidence of such a relation could be obtained with a two junctions superconducting loop: if one of them has a sin(2φ) relation, the interference pattern under magnetic field should have maxima both at integral and half-integral flux quanta [5], whereas the maxima occur only at the integral (half-integral) values if this junction is fully in the 0 (π) state [9,10]. However we chose to analyze the current-phase relation by studying the dynamic behavior of a single junction.…”

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confidence: 99%

Half-Integer Shapiro Steps at the0−πCrossover of a Ferromagnetic Josephson Junction

et al. 2004

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We investigate the current-phase relation of S/F/S junctions near the crossover between the 0 and the π ground states. We use Nb/CuNi/Nb junctions where this crossover is driven both by thickness and temperature. For a certain thickness a non-zero minimum of critical current is observed at the crossover temperature. We analyze this residual supercurrent by applying a high frequency excitation and observe the formation of half-integer Shapiro steps. We attribute these fractional steps to a doubling of the Josephson frequency due to a sin(2φ) current-phase relation. This phase dependence is explained by the splitting of the energy levels in the ferromagnetic exchange field.PACS numbers: 74.50.+r,74.45.+cThe current-phase relation of ballistic and diffusive S/N/S junctions is predicted to be strongly nonsinusoidal at zero temperature in contrast to that of tunnel junctions. This is due to a different conductivity mechanism involving Andreev bound states created in the normal metal (N) by the superconductors (S). These states are sensitive to the superconducting phase difference φ and carry the supercurrent I S . In S/F/S junctions the current-phase relation is strongly distorted by the exchange field of the ferromagnet (F) and can even be reversed leading to the famous π state [1]. The microscopic mechanism responsible for this negative supercurrent can be intuitively explained in the clean limit where the Andreev spectrum is discrete [2,3,4]. The two spin configurations of each bound state are indeed split by the ferromagnetic exchange energy. When the first bound state is shifted from finite energy to zero energy (at φ = 0), the direction of the total supercurrent given by the lowest level (for φ > 0) is negative (instead of positive). In this case the ground state is at φ = π.In this article we consider the situation where the exchange energy E ex is half that of the π junction described above for the same thickness d. In this case the Andreev spectrum of a ballistic junction contains equidistant states twice closer than usual (Fig. 1a). As a result the supercurrent is π periodic in phase with a saw-tooth shape at zero temperature (Fig. 1b) and the ground states φ = 0 and φ = π are degenerate [5]. The current-phase relation becomes more rounded in the diffusive regime (Fig. 1c) where the discrete spectrum is replaced by a continuous density of Andreev states [6]. At this 0 -π crossover the current-phase relation contains a dominant sin(2φ) component and the critical current presents a non-zero minimum with respect to thickness or exchange energy variations. Experimentally the critical current of S/F/S junctions at the crossover is however so small that it was always assumed to vanish completely. In Nb/CuNi/Nb junctions [4,7] this behavior could be related to the strong decoherence of the magnetic alloy and in Nb/PdNi/Al 2 O 3 /Nb junctions [8] to the presence of the tunnel barrier.In this Letter we report the first observation of a small non-zero critical current at the 0 -π crossover of a Nb/CuNi/Nb junction an...

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Phase Sensitive Experiments in Ferromagnetic-Based Josephson Junctions

Cited by 115 publications

References 18 publications

Recovering of superconductivity in S/F bilayers under spin-dependent nonequilibrium quasiparticle distribution

Recovering of superconductivity in S/F bilayers under spin-dependent nonequilibrium quasiparticle distribution

Non-collinear magnetoelectronics

Half-Integer Shapiro Steps at the0−πCrossover of a Ferromagnetic Josephson Junction

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