Multiple0−πtransitions in superconductor/insulator/ferromagnet/superconductor Josephson tunnel junctions

Abstract

We report on experimental studies about superconducting coupling through a thin Ni 76 Al 24 film. A patterning process has been developed, which allows in combination with the wedge shaped deposition technique the in situ deposition of 20 single Nb/ Al/ Al 2 O 3 /Ni 3 Al/ Nb multilayers, each with its own well-defined Ni 3 Al thickness. Every single multilayer consists of 10 different sized Josephson junctions, showing a high reproducibility and scaling with its junction area. Up to six damped oscillations of the critical current density against F-layer thickness were observed, revealing three single 0-transitions in the ground state of Josephson junctions. Contrary to former experimental studies, the exponential decay length is one magnitude larger than the oscillation period defining decay length. The theoretical predictions based on linearized Eilenberger equations results in excellent agreement of theory and experimental results.

Sign Reversal of AC Josephson Current in a Ferromagnetic Josephson Junction

“…In the practical case, h ex is experimentally larger than eV. [17][18][19][20][21][22][23][24][25][26][27] Therefore, the period is dominated by h ex and is short compared with 0 . The Vdependence of I c1 and I c2 in the SC/FM/SC junction shows remarkable phenomenon.…”

“…[9][10][11][12][13][14] Recently, a Josephson junction with a ferromagnetic metal (FM), which is called the ferromagnetic Josephson junction, has been actively studied both experimentally and theoretically. [15][16][17][18][19][20][21][22][23][24][25][26][27][28] One of the most interesting phenomena in the ferromagnetic Josephson junction is the oscillation of the I c1 as a function of the thickness of the ferromagnetic film. The mechanism of the oscillation is similar to that of FuldeFerrell-Larkin-Ovchinnikov (FFLO) state.…”

Theoretical Study of Magnetism Induced by Proximity Effect in a Ferromagnetic Josephson Junction with a Normal Metal

“…[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.…”

“…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]…”

Theory of Josephson effect in junctions with complex ferromagnetic/normal metal weak link region

“…First, typical values of Fermi velocities in ferromagnetic materials (see e.g. the analysis of experimental data done in [39], [40]) are of the order of 2 × 10 5 m/s, about an order of magnitude smaller than in high conductivity metals. The second factor is the rather small electron mean free path in ferromagnets, especially alloys like CuNi, PtNi, etc.…”