Zeeman ratchets for ballistic spin currents

TL;DR

This paper explores how Zeeman ratchets in a 2DEG can generate directed, spin-polarized currents without charge flow by using asymmetric magnetic fields and adiabatic driving, extending quantum charge ratchet concepts to spin.

Contribution

It introduces a novel method to produce pure spin currents in ballistic 2DEG systems using magnetic field asymmetry and adiabatic modulation, expanding the scope of quantum ratchet mechanisms.

Findings

Net spin currents can be achieved without charge currents.

Magnetic field asymmetry enables spin-selective transport.

Ballistic, coherent transport is essential for the effect.

Abstract

We investigate the possiblity of creating directed spin-polarized currents in a two-dimensional electron gas (2DEG) subject to an asymmetric magnetic field and an external adiabatic driving. We thereby generalize concepts of quantum charge ratchets to the case with spin. Due to the Zeeman term in the Hamiltonian, spin-up and -down electrons experience different effective potentials, which can be tailored to achieve net spin currents without corresponding charge currents. We consider ballistic, coherent transport in waveguides defined in a 2DEG, where the magnetic field modulation is induced by ferromagnetic stripes on top of the 2DEG.