Ubiquitous Spin-Orbit Coupling in a Screw Dislocation with High Spin Coherency

We theoretically demonstrate that screw dislocation (SD), a 1D topological defect widely present in semiconductors, exhibits ubiquitously a new form of spin-orbit coupling (SOC) effect. Differing from the widely known conventional 2D Rashba-Dresselhaus (RD) SOC effect that typically exists at surfaces or interfaces, the deep-level nature of SD-SOC states in semiconductors readily makes it an ideal SOC. Remarkably, the spin texture of 1D SD-SOC, pertaining to the inherent symmetry of SD, exhibits a significantly higher degree of spin coherency than the 2D RD-SOC. Moreover, the 1D SD-SOC can be tuned by ionicity in compound semiconductors to ideally suppress spin relaxation, as demonstrated by comparative first-principles calculations of SDs in $\mathrm{Si}/\mathrm{Ge}$, GaAs, and SiC. Our findings therefore open a new door to manipulating spin transport in semiconductors by taking advantage of an otherwise detrimental topological defect.

Figure 1

(a) The orientations of the effective electrical field (light gray shaded circle) and spins (red and blue arrows) for the conventional Rashba SOC effect at surfaces or interfaces. (b) Same as (a) for the linear Dresselhaus effect in an asymmetry QW or a strained zinc-blende film. (c) Combined effect of (a) and (b). (d) The orientations of the effective electrical field (gray arrows) and spins (red and blue arrows) for the 1D SD-SOC effect as found in Ge. (e) Same as (d) as found in GaAs. (f) Combined effect of (d) and (e) as found in SiC.

Figure 2

(a)–(c) The atomic structures of a SD in bulk Ge, GaAs, and SiC, respectively. (d)–(f) Band structures of a SD in Ge, GaAs, and SiC with SOC effect, respectively. The Fermi level is set to zero. The red and blue lines represent SD-SOC bands with different spin projections.

Figure 3

(a),(c),(e) The spin textures of SD-SOC bands obtained from DFT calculations for Ge, GaAs, and SiC, respectively. The red and blue arrows show orientations of two spin projections. The dashed-line spin textures are obtained from TB results. (b),(d),(f) Data points (dots) show $\theta$, the angle between the spin and the $+k_x$ axis, as a function of $k_z$ obtained from DFT calculations for Ge, GaAs, and SiC, respectively. The lines are drawn according to Eqs. (3b), (4b), and (5), respectively.