Evidence for the ballistic intrinsic spin Hall effect in HgTe nanostructures

In the spin Hall effect, a current passed through a spin-orbit coupled electron gas induces a spin accumulation of inverse sign on either side of the sample. A number of possible mechanisms have been described, extrinsic as well as intrinsic ones, and they may occur in the ballistic as well as the diffusive transport regime. A central problem for experimentalists in studying the effect is the very small signals that result from the spin accumulation. Electrical measurements on metals have yielded reliable signatures of the spin Hall effect, but in semiconductors the spin accumulation could only be detected by optical techniques. Here we report experimental evidence for electrical manipulation and detection of the ballistic intrinsic spin Hall effect (ISHE) in semiconductors. We perform a non-local electrical measurement in nanoscale H-shaped structures built on high-mobility HgTe/(Hg, Cd)Te quantum wells. When the samples are tuned into the p-regime, we observe a large non-local resistance signal due to the ISHE, several orders of magnitude larger than in metals. In the n-regime, where the spin-orbit splitting is reduced, the signal is at least one order of magnitude smaller and vanishes for narrower quantum wells. We verify our experimental observations by quantum transport calculations.