Spin pumping through quantum dots

Abstract

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.We propose schemes for generating spin currents into a semiconductor by adiabatic or non-adiabatic pumping of electrons through interacting quantum dots. The appeal of such schemes lies in the possibility to tune the pumping characteristics via gate voltages that control the properties of the quantum dot. The calculations are based on a systematic perturbation expansion in the tunnel-coupling strength and the pumping frequency, expressed within a diagrammatic real-time technique. Special focus is put on the possibility of pure spin pumping, i.e., of pumping spin currents without charge currents.Setup of a device for generating a spin current into a semiconductor by adiabatic or non-adiabatic pumping of electrons through an interacting quantum dot.1 Introduction A substantial aspect of semiconductor spintronics [1][2][3] is the controlled generation and manipulation of spin-polarized carriers in semiconductors. Both in the context of nanoscopic spintronic devices and quantum computation, it is highly desirable to coherently manipulate a few or even individual spins. The main objective of this article is to review some recent studies of adiabatic charge and spin pumping from a spin-polarized lead (e.g., a ferromagnetic metal, a diluted magnetic semiconductor, or a spin-polarized edge channel of a quantum Hall system) through a quantum dot with large charging energy into a (nonmagnetic) semiconductor. The ferromagnet and the semiconductor are considered as electron reservoirs. For the ferromagnet, the density of states is spin dependent. In the case in which the average single-particle level spacing in the quantum dot exceeds all other energy scales relevant to transport, such as bias voltage and temperature, only one or a few orbital levels in the quantum dot participate in transport. Coulomb interaction is accounted for by a charging energy, which typically dominates over all other energy scales in the system. Transport can occur by tunneling between quantum dot and leads. For establishing pumping through the quantum dot, some

Time-local master equation connecting the Born and Markov approximations

“…This inversion yields a changing sign of the principal value part in Eq. (36) and therefore vanishing imaginary part of the self-energy. For one contraction only the real part with one delta distribution δ(ω − E) remains.…”

Gauge freedom in observables and Landsberg's nonadiabatic geometric phase: Pumping spectroscopy of interacting open quantum systems

“…We now compute the observable as in most cited AR works [43,55,[68][69][70][133][134][135][136][137] by assuming thatX r has no parametric time dependence to begin with: setting ∂X r /∂t = 0 in Eq. (41),…”

“…II A. This approach was formulated in [55] and subsequently analyzed in detail in [68][69][70][133][134][135][136][137] and systematic higher-order corrections, beyond the Born-Markov approximation, were computed in [55,140].…”

Thermodynamics and Steady State of Quantum Motors and Pumps Far from Equilibrium

“…A suitable methodology is given by the real-time diagrammatic theory [ 78 ], which allows for an effective treatment of the quantum dot dynamics by performing a double expansion in both the tunnel coupling between the dot and the leads and the frequency associated with the external driving parameters. Since then, many extensions and application examples appeared in the context of quantum pumps [ 12 , 57 , 58 , 59 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 ] and quantum motors [ 42 ].…”