Holes in Silicon Hold On to Their Spin

Abstract

In spintronic devices [1–3], digital information is represented by the direction of the quantum-mechanical spin of the charge carriers. A spin pointing in one direction denotes a logical 0, whereas a spin pointing in the opposite direction represents the logical 1. Spintronic devices are almost exclusively fabricated out of n-type semiconductors (electrons carry the current) as opposed to p-type semiconductors (holes carry the current), which may seem surprising since both electrons and holes have spin. The reason is that holes have been assumed to be unable to preserve their spin polarization over distances longer than a few tens of nanometers. This perspective is changing, as several recent experiments have shown that hole spins in p-type silicon can be polarized and retain their polarization for a surprisingly long time. However, experiments that directly probe the spin of the holes as they travel through the material have been lacking.