Frequency-dependent current noise through quantum-dot spin valves

Abstract

We study frequency-dependent current noise through a single-level quantum dot connected to ferromagnetic leads with non-collinear magnetization. We propose to use the frequency-dependent Fano factor as a tool to detect single-spin dynamics in the quantum dot. Spin precession due to an external magnetic and/or a many-body exchange field affects the Fano factor of the system in two ways. First, the tendency towards spin-selective bunching of the transmitted electrons is suppressed, which gives rise to a reduction of the low-frequency noise. Second, the noise spectrum displays a resonance at the Larmor frequency, whose lineshape depends on the relative angle of the leads' magnetizations.

The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

“…5(b). With increasing the bias voltage further, the excited states start participating in transport and the system apparently exhibits a normal spin-valve behavior [6,7], with the current in the parallel configuration larger than in the antiparallel one and, thus, with positive TMR, see Fig. 5…”

“…The tunneling current is usually larger in the parallel configuration, when transport occurs between the majority-majority and minority-minority spin bands, than in the antiparallel configuration, where electrons tunnel between majority and minority spin bands, which gives rise to positive TMR effect. The TMR has been analyzed in various systems, including single-electron transistors and quantum dots [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. In fact, a great deal of theoretical and experimental investigations has been devoted to spin-polarized transport through quantum dot structures.…”

“…Furthermore, such systems are also being considered for applications in future spintronic devices as well as for quantum computing [21]. However, most of existing theoretical considerations of spin-dependent transport in quantum dots involved only single and double dot systems [3,4,5,6,7,8,9,10,11,12,13,14,15,16], while experiments were carried out mainly for single dot structures [22,23,24,25,26,27,28,29,30,31]. In particular, it has been shown [7] that the TMR in quantum dots weakly coupled to ferromagnetic leads is generally smaller than the value given by the Julliere model [1], TMR Jull = 2p 2 /(1 − p 2 ), where p is the spin polarization of the leads, which is characteristic of tunneling through a single tunnel junction.…”

Spin effects in single-electron tunnelling

“…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. 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].…”

Controlling spin polarization of a quantum dot via a helical edge state

“…In all these works, no dc backscattering current is found without intrinsic spin relaxation, an anisotropic Kondo coupling or Rashba impurity, due to the necessity to flip the spin in order to scatter between opposite branches of the QSH edge. This characteristic is reminiscent of QDs coupled to bulk (3D) ferromagnetic leads, where the coupling to the leads controls the QD behavior, and virtual exchange of electrons induces an exchange field on the QD parallel to the lead polarization [22][23][24] adding to possible external fields [25,26].…”