Ballistic spin field-effect transistors: Multichannel effects

TL;DR

This paper investigates how multi-channel effects influence the conductance modulation in ballistic spin field-effect transistors, revealing rapid decay of modulation ratio with increasing channels and the impact of coherence and nonideal structures.

Contribution

It provides a detailed numerical analysis of multi-channel effects on conductance modulation in SFETs, including coherence and nonideal contact influences, which were not thoroughly explored before.

Findings

Conductance modulation ratio decays rapidly with more channels.

Larger Rashba coupling accelerates the decay of modulation.

Resonance peaks from electron confinement affect conductance in nonideal structures.

Abstract

We study a ballistic spin field-effect transistor (SFET) with special attention to the issue of multi-channel effects. The conductance modulation of the SFET as a function of the Rashba spin-orbit coupling strength is numerically examined for the number of channels ranging from a few to close to 100. Even with the ideal spin injector and collector, the conductance modulation ratio, defined as the ratio between the maximum and minimum conductances, decays rapidly and approaches one with the increase of the channel number. It turns out that the decay is considerably faster when the Rashba spin-orbit coupling is larger. Effects of the electronic coherence are also examined in the multi-channel regime and it is found that the coherent Fabry-Perot-like interference in the multi-channel regime gives rise to a nested peak structure. For a nonideal spin injector/collector structure, which consists of a conventional metallic ferromagnet-thin insulator-2DEG heterostructure, the Rashba-coupling-induced conductance modulation is strongly affected by large resonance peaks that arise from the electron confinement effect of the insulators. Finally scattering effects are briefly addressed and it is found that in the weakly diffusive regime, the positions of the resonance peaks fluctuate, making the conductance modulation signal sample-dependent.