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Interference Effect on a Josephson Junction with Magnetic Interfaces
최치훈 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.9
We study the proximity effect in a superconductor-normal-superconductor (SNS) layer with spinactive interfaces, paying particular attention to the effect of interference on the transition between 0and π states of a Josephson junction. We compute the supercurrent density in the ballistic limit by using the Green’s function formalism without making the quasiclassical approximation to study the interference effect due to coherent scattering of quasiparticles from the interfaces. The supercurrent is strongly influenced by various factors such as the thickness of the normal layer, the strength of the interface potential, and the orientation of the interface spin. We also discuss the symmetry of the induced superconducting pair amplitude for the 0 and the π states. The detailed features of the effect of interference on the Josephson junction can be important for applications of quantum devices.
최치훈 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.9
We study the proximity effect in a multilayer composed of a normal metal and a superconductor with spin-active interfaces. The symmetry of the induced pair amplitude is analyzed while varying the interface distance and the direction of the interface spins. We apply the general Green’s function formalism without making the quasiclassical approximation in order to study the interference effect from the surrounding interfaces of the superconducting layer. By utilizing the formalism developed by A. Millis <i>et al.</i>, we compute the Keldysh Green’s function while incorporating the general boundary condition for magnetic interfaces of a superconducting heterostructure. The interference can have a profound effect on the proximity phenomena in the ballistic limit when the interface distance becomes less than the superconducting coherence length. We also discuss the effect of the direction of the interface spins on the induction of the odd-frequency equal-spin pairing state, which is important for applications of ferromagnetic quantum devices.
Josephson Effect in a Singlet Superconductor-Ferromagnet-Triplet Superconductor Junction
최치훈 한국물리학회 2017 New Physics: Sae Mulli Vol.67 No.12
We study the current-phase relation of a ballistic SIFIT junction, consisting of a spin-singlet superconductor (S), an insulating ferromagnetic interface (I), a weak ferromagnetic metal (F), another insulating ferromagnetic interface (I), and a spin-triplet superconductor (T). We use the generalized quasiclassical formalism developed by Millis $et al.$ to compute the current density and the free energy of the junction for arbitrary orientations of the magnetizations of the junction barrier. We investigate in detail the effect of the distribution of magnetization on the various harmonics of the current-phase relation and the transition of the ground state of the junction. A magnetization parallel to the d-vector of the triplet superconductor can lead to an anomalous Josephson current and a transition of the ground state from the $\pi/2$-state to the $3 \pi/2$-state. The $\phi$-state junction can be realized for a noncollinear orientation of the barrier magnetizations in the plane perpendicular to the d-vector.