Stern‐Gerlach effect and spin filtering in the solid state

Abstract

PACS 71.70. Ej, 72.25.Dc, 73.23.Ad Our recent experimental and theoretical works on Stern-Gerlach devices and spin filters built of GaAs and PbTe materials are reviewed. It is shown that for high mobility electrons at the GaAs/(Al,Ga)As interface, the Stern-Gerlach effect can be observed in appropriately designed ballistic nanostructers with in-plane local magnetic field produced by micromagnets of ferromagnetic metals. The spin separation is possible owning to the cancellation of Lorentz force and g-factor enhancement caused by the electron-electron interaction and 1D confinement. Due to a large spin-orbit coupling in PbTe, which results in |g * | ≈ 66, the spinsplitting can become larger than 1D quantization energy in rather weak magnetic fields. Evidences for generation of spin polarised current carried by many 1D subbands in PbTe nanoconstrictions are described.1 Introduction According to the well established quasi-classical arguments [1] the Stern-Gerlach (S-G) effect can not be observed for beams of electrons because of the unavoidable distortions introduced by the Lorentz force. The more recent quantum approaches to this fundamental problem suggested, however, that the (S-G) experiment is difficult but possible for specially prepared electron wave packets [2][3][4]. At the same time it turned out that the physics of electron beams propagating freely in vacuum can provide a sound starting point in the process of developing solid state spintronic devices because of the long spin coherence times in semiconductors [5]. For example, (S-G) effect has been theoretically considered as a possible readout gate in spin-logic processors [6]. The spin filters are also necessary for the Bell inequalities violations tests suggested for the Cooper pair components injected to semiconductor via the Andreev process [7,8]. Also, the progress in fabrication of hybrid ferromagnet-semiconductor microstructures [9, 10] has made it possible to address various aspects of a single-electron motion in the presence of an inhomogeneous magnetic field [11][12][13][14][15][16][17].Such approach, however, should be complemented by taking into account substantial differences between a quasi-classical motion in vacuum and quantum transport in low-dimensional solids, such as the self-consistent nature of a one-electron confining potential, exchange interaction in Fermi liquid, renormalization of the Landé factor and spin-orbit (S-O) effects. In this paper we summarise the outcome of our recent works in which we aimed to take advantage of such differences when developing spin polarizers of semiconductor nanostructures. Experimentally, we studied the effect of a local in-plane magnetic field on ballistic currents in a quantum wire patterned of GaAs/(Al,Ga)As heterostructure. The results are obtained for a ferromagnet-semiconductor hybrid device which is highly optimized in order to toggle between uniform field and field gradient internal spin barriers. The observed effects are attributed to switching between Zeeman and Stern-Gerlach modes -t...

Stern-Gerlach Forces and Spin Splitters

“…On the other hand the so-called "continuous SG effect" has been used for measurements in magnetic traps of the magnetic moment of the free electron [7,8,9] and of electrons bound in atomic ions [10]. Moreover, spin splitting of electron systems by SG forces might be occuring in special materials [11,12]. Some discussion of quantum effects in storage rings can be found in [17,18].…”