Modulating Unpolarized Current in Quantum Spintronics: Visibility of Spin-Interference Effects in Multichannel Aharonov-Casher Mesoscopic Rings

摘要

The conventional unpolarized current injected into a {\em quantum-coherent}semiconductor ring attached to two external leads can be modulated from perfectconductor to perfect insulator limit via Rashba spin-orbit (SO) coupling. Thisrequires that ballistic propagation of electrons, whose spin precession isinduced by the Aharonov-Casher phase, takes place through a single conductingchannel ensuring that electronic quantum state remains a pure separable one inthe course of transport. We study the fate of such spin interference effects asmore than one orbital conducting channel becomes available for quantumtransport. Although the conductance of multichannel rings, in general, does notgo all the way to zero at any value of the SO coupling, some degree of currentmodulation survives. We analyze possible scenarios that can lead to reducedvisibility of spin interference effects that are responsible for the zeroconductance at particular values of the Rashba interaction: (i) the transmittedspin states remain fully coherent, but conditions for destructive interferenceare different in different channels; (ii) the transmitted spins end up inpartially coherent quantum state arising from entanglement to the environmentcomposed of orbital degrees of freedom of the same particle to which the spinis attached.