Abstract
Semiconductors with strong spin–orbit interaction as the underlying mechanism for the generation of spin-polarized electrons are showing potential for applications in spintronic devices. Unveiling the full spin texture in momentum space for such materials and its relation to the microscopic structure of the electronic wave functions is experimentally challenging and yet essential for exploiting spin–orbit effects for spin manipulation. Here we employ a state-of-the-art photoelectron momentum microscope with a multichannel spin filter to directly image the spin texture of the layered polar semiconductor BiTeI within the full two-dimensional momentum plane. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the valence and conduction band electrons in BiTeI have spin textures of opposite chirality and of pronounced orbital dependence beyond the standard Rashba model, the latter giving rise to strong optical selection-rule effects on the photoelectron spin polarization. These observations open avenues for spin-texture manipulation by atomic-layer and charge carrier control in polar semiconductors.
Highlights
Semiconductors with strong spin–orbit interaction as the underlying mechanism for the generation of spin-polarized electrons are showing potential for applications in spintronic devices
Strong spin–orbit effects can be achieved in these compounds by incorporation of heavy atoms, such as in Bi2Te3 and Bi2Se3 that realize topological insulators with non-trivial spin-polarized surface states[3]
This implies the possibility to modify the spin texture through control of the charge carrier type, which, in BiTeI, could be realized through n-type and p-type band bending in dependence of surface termination[18]
Summary
Semiconductors with strong spin–orbit interaction as the underlying mechanism for the generation of spin-polarized electrons are showing potential for applications in spintronic devices. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the valence and conduction band electrons in BiTeI have spin textures of opposite chirality and of pronounced orbital dependence beyond the standard Rashba model, the latter giving rise to strong optical selection-rule effects on the photoelectron spin polarization These observations open avenues for spin-texture manipulation by atomic-layer and charge carrier control in polar semiconductors. Our measurements reveal opposite spin chiralities for electronic states at the valence band top and at the conduction band bottom, despite the fixed polar electric field vector determined by the (BiTe) þ -I À stacking sequence This implies the possibility to modify the spin texture through control of the charge carrier type, which, in BiTeI, could be realized through n-type and p-type band bending in dependence of surface termination[18]. This manifests itself in pronounced changes of the measured photoelectron spin textures depending on the polarization of the exciting light, which are in sharp contrast to the metallic Rashba system Au(111)[22,26] but in remarkable correspondence to recent findings in the topological insulator Bi2Se3 (refs 26,27)
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