The presence of both inversion (P ) and time-reversal (T ) symmetries in solids leads to well-known double degeneracy of electronic bands (Kramers degeneracy). When the degeneracy is lifted, spin textures can be directly observed in momentum space, as in topological insulators or in strong Rashba materials. The existence of spin textures with Kramers degeneracy, however, is very difficult to observe directly. Here, we use quantum interference measurements combined with first-principle band structure calculations to provide evidence for the existence of hidden entanglement between spin and momentum in antiperovskite-type 3D Dirac material Sr3SnO. We find robust weak antilocalization (WAL) independent of the position of EF, whereas clear signature of weak localization (WL) develops only when EF shifts away from the Dirac node by doping. The observed WAL signal at low doping is fitted using a single interference channel which implies that the different Dirac valleys are mixed by disorder. Notably, this mixing does not suppress WAL, suggesting contrasting interference physics compared to graphene. We identify scattering among axially spin-momentum locked states as a key process that leads to a spin orbital entanglement, giving rise to robust WAL. Our work sheds light on the subtle role of spin and pseudospin when both could contribute to the same quantum effect. arXiv:1806.08712v1 [cond-mat.mes-hall]

The class of antiperovskite compounds A3BO (A = Ca, Sr, Ba; B = Sn, Pb) has attracted interest as a candidate 3D Dirac system with topological surface states protected by crystal symmetry. A key factor underlying the rich electronic structure of A3BO is the unusual valence state of B, i.e., a formal oxidation state of −4. Practically, it is not obvious whether anionic B can be stabilized in thin films, due to its unusual chemistry, as well as the polar surface of A3BO, which may render the growth-front surface unstable. We report X-ray photoelectron spectroscopy (XPS) measurements of single-crystalline films of Sr3SnO and Sr3PbO grown by molecular beam epitaxy (MBE). We observe shifts in the core-level binding energies that originate from anionic Sn and Pb, consistent with density functional theory (DFT) calculations. Near the surface, we observe additional signatures of neutral or cationic Sn and Pb, which may point to an electronic or atomic reconstruction with possible impact on putative topological surface states. * d.huang@fkf.mpg.de † hnakamur@uark.edu; Present address:

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We report a first-principles investigation of the atomic and electronic properties at the perfect and defective (001) surfaces of the antiperovskite Sr3SnO. We first performed a thermodynamical study of the atomic structure terminations and demonstrated that SrSn-terminated surfaces should be the most stable one, either with a perfect (1 × 1) structure or with a (2 × 1) reconstruction induced by the formation of Sn vacancies. We detailed the surface gap states obtained for these surfaces, which we compare with those of other surface terminations, also having relatively low energies. These gap states, located near the Fermi level, could have a major contribution to the transport properties. Due to the lack of inversion symmetry associated with the surface, we predict that they also experience spin splittings, an important property for spinorbitronic applications. Finally, we found that Sr2O-terminated surfaces could display a ferromagnetic ordering resulting from the population of 4d orbitals of Sr atoms at the surface and that this could lead to the formation of a spin-polarized two-dimensional electron gas.

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