Spin-dependent Andreev reflection tunneling through a quantum dot with intradot spin-flip scattering

Abstract

We study Andreev reflection (AR) tunneling through a quantum dot (QD) connected to a ferromagnet and a superconductor, in which the intradot spin-flip interaction is included. By using the nonequibrium-Green-function method, the formula of the linear AR conductance is derived at zero temperature. It is found that competition between the intradot spin-flip scattering and the tunneling coupling to the leads dominantes resonant behaviours of the AR conductance versus the gate voltage. A weak spin-flip scattering leads to a single peak resonance. However, with the spin-flip scattering strength increasing, the AR conductance will develop into a double peak resonannce implying a novel structure in the tunneling spectrum of the AR conductance.Besides, the effect of the spin-dependent tunneling couplings, the matching of Fermi velocity, and the spin polarization of the ferromagnet on the AR conductance is eximined in detail.

Andreev Reflection in Transport through a Quantum Dot Coupled to Ferromagnetic and Superconducting Electrodes

“…2 of Ref. [3], and is a consequence of the fact that the dot states taking part in transport are then superpositions of spin-up and spin-down states. When the coupling strength Γ f0 increases, then for the specic case of Γ f0 = Γ s0 one observes perfect AR tunneling processes at ε d = 0, as shown by the solid line for B = 0 in the middle part in Fig.…”

“…The Andreev reection in transport through a QD coupled to two ferromagnetic electrodes and a superconductor revealed some interesting properties associated with the matching condition for maximum (4e 2 /h) linear conductance and the magnetoresistance effect. It has been also predicted that for strong enough spin-ip interaction in the dot, the interplay of spin properties of the AR processes and spin dependent electronic transport leads to a double-peak structure in the linear conductance [3]. Moreover, it has been shown that when the electronphonon interactions in the dot are taken into account, new peaks appear on both sides of the main AR conductance peak [4].…”

“…Making use of the nonequilibrium Green-function technique in the 4 × 4 Nambu representation [5], one can calculate the current due to the Andreev reection from the formula [3,5]:…”

“…The main objective of this paper is to extend previous studies of the hybrid FQDS systems [3] where the eect of intradot spin-ip processes on the AR linear conductance was examined in detail by considering the Andreev reection phenomenon in the context of the interplay between tunneling processes, intradot spin-ip transitions and Zeeman spin-splitting of the discrete energy level of the dot. Moreover, both linear as well as nonlinear transport regimes are considered.…”

Phonon-assisted Andreev reflection in a hybrid junction based on a quantum dot

“…The symbol P in equation (28) is the spin polarization factor, the quantity Γ f 0 (Γ s0 ) determines the coupling strength between the dot and the ferromagnetic (superconducting) lead, while the symbol ρ s denotes the BCS density of states [18]:…”