Two copies of spin helices with stretching pitch and compensating helicity

Abstract

Persistent spin helix (PSH) manifests itself as an effective knob to tackle spin decay inevitably occurring in disordered two-dimensional electron gases. Here, for ordinary (110)-oriented two-subband GaInAs wells subjected to top and back gate voltages, we theoretically achieve adjusting the Dresselhaus terms of the two bands while meanwhile consistently pinning the system at symmetric configuration [i.e., locking the Rashba spin-orbit (SO) terms to zero], thus enabling simultaneous formation of two copies of PSHs of flexible control. Strikingly, we are able to stretch the pitch---spin density wave length---of PSH by far more than one period, enabling helix-stretch functional spin field-effect transistor (FET), with both on and off states protected by the PSH symmetry. Moreover, we attain a scenario in which the helicities of the two copies of PSHs are sufficiently compensated. This makes possible a new concept: ``orbit (band) filter,'' which resembles spin FET while with novel functionality of orbit filtering, opening up a new route towards spintronic and orbitronic combined applications.