Nonequilibrium Kondo effect in a quantum dot coupled to ferromagnetic leads

Abstract

We study the Kondo effect in the electron transport through a quantum dot coupled to ferromagnetic leads, using a real-time diagrammatic technique which provides a systematic description of the nonequilibrium dynamics of a system with strong local electron correlations. We evaluate the theory in an extension of the 'resonant tunneling approximation', introduced earlier, by introducing the self-energy of the off-diagonal component of the reduced propagator in spin space. In this way we develop a charge and spin conserving approximation that accounts not only for Kondo correlations but also for the spin splitting and spin accumulation out of equilibrium. We show that the Kondo resonances, split by the applied bias voltage, may be spin polarized. A left-right asymmetry in the coupling strength and/or spin polarization of the electrodes significantly affects both the spin accumulation and the weight of the split Kondo resonances out of equilibrium. The effects are observable in the nonlinear differential conductance. We also discuss the influence of decoherence on the Kondo resonance in the frame of the real-time formulation.

Spin effects in single-electron tunnelling

“…Spin-polarized transport in the cotunneling regime has also been addressed for collinear systems [154,155,156,157], as well as for systems magnetized non-collinearly [158,159,160,161]. Furthermore, the resonant tunnelling was also considered [142,162].…”

“…The real-time diagrammatic technique [104,167] enables one to construct a systematic approach, where the effect of ferromagnetic electrodes can be analyzed without any additional assumptions. Recently the resonant tunnelling approximation (RTA) was extended by Utsumi et al [142] to account for influence of the electrodes' ferromagnetism on the Kondo phenomenon. This technique gives more reasonable results and allows for further systematic insight into the physics of the transport through quantum dots in the Kondo regime.…”

“…spin accumulation, parity effect on tunnel magnetoresistance, zero-bias anomaly in the Coulomb blockade regime, exchange field, splitting of the Kondo anomaly, and others. Most of the works concerned theoretical description of spin-polarized transport in the weak coupling regime, as well as in the strong coupling regime, where the Kondo physics emerges [137,138,139,140,141,142,143,144,145]. Sequential transport through a single-level quantum dot coupled to ferromagnetic leads was studied for both collinear [146,147] and non-collinear [148,149,150,151,152,153] configurations of the electrodes' magnetic moments.…”

Thermoelectric effects in strongly interacting quantum dot coupled to ferromagnetic leads

“…Recently we observe growing interest in electronic * Electronic address: krawiec@kft.umcs.lublin.pl † Electronic address: karol@tytan.umcs.lublin.pl transport properties of the Kondo correlated quantum dots coupled to ferromagnetic electrodes [16]- [30]. In such geometry the Kondo resonance splits in parallel configuration [17,23,24,25] (however, some of the works [19,22] predict no splitting), while in the anti-parallel configuration the Kondo effect remains virtually the same as for nonmagnetic electrodes.…”

Dimensionality effects in the local density of states of ferromagnetic hosts probed via STM: Spin-polarized quantum beats and spin filtering

“…24 In the condensed-matter literature on scanning microscopy, there is a profusion of work discussing spin-dependent phenomena employing ferromagnetic leads coupled to quantum dots or adatoms in the Kondo regime. 4,6,7,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] Here, we mention those with metallic samples and buried impurities in which the anisotropy of the Fermi surface plays an important role in electron tunneling. [45][46][47][48][49][50] According to the experiment of Prüser et al, 45 such anisotropy allows atoms of Fe and Co beneath the Cu(100) surface to scatter electrons in preferential directions of the material due to an effect called "electron focusing."…”