Large spin splittings due to the orbital degree of freedom and spin textures in a ferroelectric nitride perovskite

Abstract

First-principles simulations are conducted to predict that ferroelectric nitride perovskite LaWN 3 not only exhibits large spin splittings (2.7 eV Å) but also possesses unique spin textures for some of its conduction levels. Such spin splittings around the and L points cannot be interpreted as a typical mixture of Rashba or Dresselhaus configurations but rather require the development of four-band k • p models with high-order terms. We further identify that, for some bands, spin splittings can be greatly contributed by the pure orbital degree of freedom (PODF), a unique character of our four-band Hamiltonian compared to the traditional two-band version. The concept of PODF-enhanced spin splittings paves a way for designing materials with large spin splittings. Moreover, the energy levels possessing such large splittings and complex spin textures can be brought close to the conduction-band minimum by applying epitaxial strain.

Purely Cubic Spin Splittings with Persistent Spin Textures

“…Symmetry analysis of the two-band Hamiltonian.-Let us recall that our target is to find possible candidates with SEPCSS, limiting ourselves within the two-band effective Hamiltonian [32] incorporating only the spin degree of freedom (i.e., the degeneracy of orbital degree of freedom, albeit important in some cases [56], is not considered). Our strategy is to derive the possible symmetry-allowed lowest order in k spin-splitting terms, case by case by exhausting all the 32 crystallographic point groups.…”

Full-plane persistent spin textures with cubic order intrinsic and anisotropic band splitting in bulk Lead-free materials

“…By fitting the DFT calculated band structure and spin texture around the M point, we find that γ = 3.1 eVÅ. This splitting is significantly larger as compared to other bulk systems such as BiTeCl (α R = 1.2 eVÅ) 42 , BiAlO 3 (α R = 0.74 eVÅ) 12 and LaWN 3 (α R = 2.7 eVÅ) 21,43 .…”

Rashba spin splitting and anomalous spin textures in the bulk ferroelectric oxide perovskite KIO3

“…We have used normal distribution for f (k x , k y , k z ) centered at (k x , k y , k z ) point to get better fit near HSP as used in Ref. 47,48 The range of k x and k y used for fitting the DFT band structures is -0.125 to 0.125 Å −1 . The coordinate convention used for calcu-…”

“…The Rashba coefficients calculated using k.p model are fairly close to the DFT predictions and shown in Table3. For splitting near A, we have used the four-band model derived using method of invariants satisfying the C 3v point group symmetry47 (see section V of SI)…”