Ferri-chiral compounds with potentially switchable Dresselhaus spin splitting

This is the authors' abstract. We don't add key points for this paper.

Spin splitting of energy bands can be induced by relativistic spin-orbit interactions in materials without inversion symmetry. Whereas polar space-group symmetries permit Rashba (R-1) spin splitting with helical spin textures in momentum space, which could be reversed upon switching a ferroelectric polarization via applied electric fields, the ordinary Dresselhaus effect (D-1A) is active in materials exhibiting nonpolar noncentrosymmetric crystal classes with atoms occupying exclusively nonpolar lattice sites. Consequently, the spin-momentum locking induced by D-1A is not electric field switchable. Here we find a type of ferri-chiral materials with an alternative type of Dresselhaus symmetry, referred to as D-1B, exhibiting crystal class constraints similar to D-1A (all dipoles add up to zero), but unlike D-1A, at least one polar site is occupied. The spin splitting is associated with the crystalline chirality, which in principle could be reversed upon a change in chirality. Focusing on alkali metal chalcogenides, we identify NaCu₅S₃ in the nonenantiomorphic ferri-chiral structure, which exhibits CuS₃ chiral units differing in the magnitude of their Cu displacements. We then synthesize NaCu₅S₃ (space group P6₃22) and confirm its ferri-chiral structure with powder x-ray diffraction. Our electronic structure calculations demonstrate it exhibits D-1B spin splitting as well as a ferri-chiral phase transition, revealing spin splitting interdependent on chirality. Our electronic structure calculations show that a few percent biaxial tensile strain can reduce (or nearly quench) the switching barrier separating the monodomain ferri-chiral P6₃22 states. We compute the circular dichroism absorption spectrum of the two ferri-chiral orientations and discuss what type of external stimuli might switch the chirality so as to reverse the (nonhelical) Dresselhaus D-1B spin texture. Our study suggests the design of ferri-chiral crystals as potential spintronic and optoelectronic materials.