Long-range current-induced spin accumulation in chiral crystals

Abstract

The chirality-induced spin selectivity (CISS) refers to a conversion between charge and spin currents occurring in chiral molecules and solids, which reveals a great potential for applications in various areas of technology. Nevertheless, after two decades of studies, the understanding of its microscopic origin remains elusive. Here, the CISS effect in materials with strong spin-orbit coupling is explained in terms of the unconventional current-induced spin accumulation, an analog of the Rashba-Edelstein effect that may manifest in systems with a radial spin texture reversing the sign for opposite enantiomers. The calculations of spin accumulation based on the density functional theory, performed for the first time for Te and TaSi2, provide a rationale for the experimental studies reporting CISS in these materials. The analysis of a general Weyl-type spin-orbit coupling locally describing the spin texture at specific momentum vectors, reveals that a quasi-persistent spin helix emerges in the real space as a consequence of the crystal symmetries, and prevents the spins from decoherence, which qualitatively supports the observation of the long-range spin transport in CISS experiments. These results open the perspectives for DFT calculations of CISS for any chiral crystals and represent a step forward to its understanding in general systems.

Ferroelectric control of charge-to-spin conversion in WTe$_{2}$

“…The magnitude at E F , χ xy (E F ) = 0.55 ×10 10 e 1 eVcm means that a charge current of 100 A/cm 2 , will generate the spin accumulation of 0.55 × 10 12 /cm 3 . Although the values of REE reported for different materials are very scarce, we can still compare the result with the previously calculated spin accumulation for Te (∼ 10 13 /cm 3 ) and the Weyl semimetal TaSi 2 (0.4 × 10 12 /cm 3 ) [27]. It is evident that CSC in WTe 2 resembles more the latter, which can be attributed to the presence of states with opposite spin polarization around the Fermi level, that generate the opposite contribution to the spin accumulation.…”

“…The Brillouin zones (BZ) were sampled on the Monkhorst-Pack k-point grids of 16×10×4 and 16×10×1. The post-processing calculations of REE were performed in the framework of semi-classical Boltzmann transport theory using the paoflow code [25,26], following the details given elsewhere [27]. The ultra-dense k-grids of 216 × 144 × 6 and 176 × 96 × 1 were employed to interpolate the Hamiltonian for the accurate convergence of REE.…”

“…The two ground states with opposite ferroelectricity can be switched under an out-of-plane electrical bias, which additionally leads to the sign reversal of spin texture, similarly as in ferroelectric Rashba semiconductors [37][38][39]. Because the Rashba-Edelstein effect directly depends on the spin operator [27], one can expect that the sign of spin accumulation could be externally manipulated via the changes in electric polarization. Such mechanism is pictorially explained in Fig.…”

Ferroelectric control of charge-to-spin conversion in WTe2

“…The Brillouin zones (BZ) were sampled on the Monkhorst-Pack k-point grids of 16 × 10 × 4 and 16 × 10 × 1. The postprocessing calculations of REE were performed in the framework of semi-classical Boltzmann transport theory using the PAOFLOW code [25,26], following the details given elsewhere [27]. The ultra-dense k-grids of 216 × 144 × 6 and 176 × 96 × 1 were employed to interpolate the Hamiltonian for the accurate convergence of REE.…”

“…The two ground states with opposite ferroelectricity can be switched under an outof-plane electrical bias, which additionally leads to the sign reversal of spin texture, similarly as in ferroelectric Rashba semiconductors [37][38][39]. Because the Rashba-Edelstein effect directly depends on the spin operator [27], one can expect that the sign of spin accumulation could be externally manipulated via the changes in electric polarization. Such a mechanism is pictorially explained in Fig.…”