Thickness Dependence of the Josephson Ground States of Superconductor-Ferromagnet-Superconductor Junctions

Oboznov, V. A.; Bolginov, V. V.; Feofanov, A. K.; Ryazanov, V. V.; Buzdin, Alexandre I.

doi:10.1103/physrevlett.96.197003

Cited by 296 publications

(339 citation statements)

References 20 publications

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“…where ξ F 1,F 2 = ξ F / √ 1 + α 2 ± α are the decay and oscillation lengths of order parameter [20], ξ F = D/E ex is the decay/oscillation length without spinflip scattering [19], E ex is the exchange energy, α = 1/(τ s E ex ), τ s is the inelastic magnetic scattering time [21] and γ B2 is the transparency parameter of the SIF part treated like a single interface. d dead F is the magnetic dead layer thickness.…”

mentioning

confidence: 99%

High quality ferromagnetic 0 and π Josephson tunnel junctions

Weides¹,

Kemmler

Goldobin

et al. 2006

Applied Physics Letters

138

149

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We fabricated high quality Nb/Al2O3/Ni0.6Cu0.4/Nb superconductor-insulator-ferromagnetsuperconductor Josephson tunnel junctions. Depending on the thickness of the ferromagnetic Ni0.6Cu0.4 layer and on the ambient temperature, the junctions were in the 0 or π ground state. All junctions have homogeneous interfaces showing almost perfect Fraunhofer patterns. The Al2O3 tunnel barrier allows to achieve rather low damping, which is desired for many experiments especially in the quantum domain. The McCumber parameter βc increases exponentially with decreasing temperature and reaches βc ≈ 700 at T = 2.11 K. The critical current density in the π state was up to 5 A/cm 2 at T = 2.11 K, resulting in a Josephson penetration depth λJ as low as 160 µm. Experimentally determined junction parameters are well described by theory taking into account spin-flip scattering in the Ni0.6Cu0.4 layer and different transparencies of the interfaces. , which is self-biased and well decoupled from the environment, one needs to use high quality π JJs with high resistance (to avoid decoherence) and reasonably high critical current density j c (to have the Josephson energy E J ≫ k B T for junction sizes of few microns or below). High j c is also required to keep the Josephson plasma frequency ω p ∝ √ j c , which plays the role of an attempt frequency in the quantum tunneling problem, on the level of a few GHz.The concept of π JJs was introduced long ago[5, 6], but only recently superconductor-ferromagnet-superconductor (SFS) π JJs were realized [7,8]. Unfortunately SFS π JJs are highly overdamped and cannot be used for applications where low dissipation is required. The obvious way to decrease damping is to make a SFS-like tunnel junction, i.e. a superconductor-insulator-ferromagnet-superconductor (SIFS) junction. Due to the presence of the tunnel barrier the critical current I c in SIFS is lower than in SFS, but both the resistance R (at I I c ) and the I c R product are much higher. Moreover, the value of I c and R can be tuned by changing the thickness d I of the insulator (tunnel barrier).

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mentioning

confidence: 99%

High quality ferromagnetic 0 and π Josephson tunnel junctions

Weides¹,

Kemmler

Goldobin

et al. 2006

Applied Physics Letters

138

149

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“…The length was comparable or shorter than the Josephson penetration depth λ J . We investigated the thickness dependence of the critical current I c (d ≫ k B T c , like in NiCu alloys, the temperature dependence of scattering provides the dominant mechanism for the I c (T ) dependence [20]. The oscillation period ξ F 2 becomes shorter for decreasing temperature, thus the whole I c (d F ) dependence is squeezed to thinner F-layer thicknesses.…”

Section: Sifs Junctions Without Step-like F-layermentioning

confidence: 99%

Ferromagnetic 0–π Josephson junctions

Weides¹,

Kohlstedt²,

Waser³

et al. 2007

Appl. Phys. A

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We present a study on low-T c superconductorinsulator-ferromagnet-superconductor (SIFS) Josephson junctions. SIFS junctions have gained considerable interest in recent years because they show a number of interesting properties for future classical and quantum computing devices. We optimized the fabrication process of these junctions to achieve a homogeneous current transport, ending up with high-quality samples. Depending on the thickness of the ferromagnetic layer and on temperature, the SIFS junctions are in the ground state with a phase drop either 0 or π. By using a ferromagnetic layer with variable step-like thickness along the junction, we obtained a so-called 0-π Josephson junction, in which 0 and π ground states compete with each other. At a certain temperature the 0 and π parts of the junction are perfectly symmetric, i.e. the absolute critical current densities are equal. In this case the degenerate ground state corresponds to a vortex of supercurrent circulating clock-or counterclockwise and creating a magnetic flux which carries a fraction of the magnetic flux quantum Φ 0 .

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“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][20][21][22] Here, D F and h ex are the diffusion coefficient and the exchange field in the F, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…1,2) The proximity effect in s-wave superconductor/ferromagnetic metal (S/F) hybrid junctions provides interesting phenomena which are not observed in S/N hybrid junctions and thus has been extensively studied both theoretically and experimentally. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] In a S/F junction, due to the proximity effect, spin-singlet Cooper pairs (SSCs) penetrate into the F. Because of the exchange splitting of the electronic density of states for up and down electrons, the SSC in the F acquires the finite center-of-mass momentum, and the pair amplitude shows a damped oscillatory behavior with the thickness of the F. [20][21][22] Interesting phenomenon induced by the damped oscillatory behavior of the pair amplitude is a π-state in a S/F/S junction, where the current-phase relation in the Josephson current is shifted by π from that of the ordinary S/I/S and S/N/S junctions (called 0-state). [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]…”

Section: Introductionmentioning

confidence: 99%