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]

A series of anti-perovskites including Sr3PbO are recently predicted to be a three-dimensional Dirac material with a small mass gap, which may be a topological crystalline insulator. Here, we report the epitaxial growth of Sr3PbO thin films on LaAlO3 using molecular beam epitaxy. X-ray diffraction indicates (001) growth of Sr3PbO, where [110] of Sr3PbO matches [100] of LaAlO3. Measurements of the Sr3PbO films with parylene/Al capping layers reveal a metallic conduction with p-type carrier density of ∼1020 cm−3. The successful growth of high quality Sr3PbO film is an important step for the exploration of its unique topological properties.

Purely cubic spin splittings in the band structure of bulk insulators have not been extensively investigated yet despite the fact that they may pave the way for novel spin-orbitronic applications and can also result in a variety of promising spin phenomena. By symmetry analysis and first-principles simulations, we report symmetry-enforced purely cubic spin splittings (SEPCSS) that can even lead to persistent spin textures. In particular, these SEPCSS can be thought to be complementary to the cubic Rashba and cubic Dresselhaus types of spin splittings. Strikingly, the presently discovered SEPCSS are expected to exist in the large family of materials crystallizing in the 6m2 and 6 point groups, including the Ge

We present the electronic and structural properties of monolayer WSe2 grown by pulsed-laser deposition on monolayer graphene (MLG) on SiC. The spin splitting in the WSe2 valence band at K was ∆SO = 0.469 ± 0.008 eV by angle-resolved photoemission spectroscopy (ARPES). Synchrotron-based grazing-incidence inplane X-ray diffraction (XRD) revealed the in-plane lattice constant of monolayer WSe2 to be aWSe 2 = 3.2757 ± 0.0008Å. This indicates a lattice compression of −0.19% from bulk WSe2. By using experimentally determined graphene lattice constant (aMLG = 2.4575 ± 0.0007Å), we found that a 3×3 unit cell of the slightly compressed WSe2 is perfectly commensurate with a 4×4 graphene lattice with a mismatch below 0.03%, which could explain why the monolayer WSe2 is compressed on MLG. From XRD and first-principles calculations, however, we conclude that the observed size of strain is negligibly small to account for a discrepancy in ∆SO found between exfoliated and epitaxial monolayers in earlier ARPES. In addition, angle-resolved, ultraviolet and X-ray photoelectron spectroscopy shed light on the band alignment between WSe2 and MLG/SiC and indicate electron transfer from graphene to the WSe2 monolayer. As further revealed by atomic force microscopy, the WSe2 island size depends on the number of carbon layers on top of the SiC substrate. This suggests that the epitaxy of WSe2 favors the weak van der Waals interactions with graphene while it is perturbed by the influence of the SiC substrate and its carbon buffer layer. arXiv:1912.04770v1 [cond-mat.mtrl-sci]

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: