Fig. 4: NLO spin current on the (0 0 1) surface of SnTe.
From: Pure spin photocurrent in non-centrosymmetric crystals: bulk spin photovoltaic effect
a The atomic structure of SnTe. In the left panel the {0 0 1} face is painted in light green, which possesses double mirror symmetries \({{\mathcal{M}}}^{x}\,\) and \({{\mathcal{M}}}^{y}\). The dashed box in the right panel indicates the primitive cell on the surface. b The surface spectrum function \(A({\boldsymbol{k}},\omega )\) on high-symmetry lines in the BZ. The gapless surface states can be observed. c The surface spectrum function \(A({\boldsymbol{k}},\omega )\) over the BZ for selected \(\omega =-0.2,\;0,\) and \(0.2\,{\mathrm{eV}}\). \({k}_{x}\) and \({k}_{y}\) are in the unit of reciprocal lattices. The surface spin textures are indicated by the black arrows. Color scheme (red to blue) in (b, c) represents surface state contribution. The color bars are in logarithmic scale, and the energy is offset to the valence band maximum. d The NLO spin current conductivity with \(x\) and \(y\) spin polarizations. Note that all charge and spin-\(z\) current components are vanishing due to \({{\mathcal{M}}}^{x}\,\) and \({{\mathcal{M}}}^{y}\).
