We demonstrate clear weak anti-localization (WAL) effect arising from induced Rashba spin-orbit coupling (SOC) in WS2-covered single-layer and bilayer graphene devices. Contrary to the uncovered region of a shared single-layer graphene flake, WAL in WS2-covered graphene occurs over a wide range of carrier densities on both electron and hole sides. At high carrier densities, we estimate the Rashba SOC relaxation rate to be ∼ 0.2ps −1 and show that it can be tuned by transverse electric fields. In addition to the Rashba SOC, we also predict the existence of a'valley-Zeeman' SOC from first-principles calculations. The interplay between these two SOC's can open a non-topological but interesting gap in graphene; in particular, zigzag boundaries host four sub-gap edge states protected by time-reversal and crystalline symmetries. The graphene/WS2 system provides a possible platform for these novel edge states.

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Proximity effects induced in the 2D Dirac material graphene potentially open access to novel and intriguing physical phenomena. Thus far, the coupling between graphene and ferromagnetic insulators has been experimentally established. However, only very little is known about graphene's interaction with antiferromagnetic insulators. Here, we report a low temperature study of the electronic properties of high quality van der Waals heterostructures composed of a single graphene layer proximitized with -RuCl 3 . The latter is known to become antiferromagnetically ordered below 10 K. Shubnikov de Haas oscillations in the longitudinal resistance together with Hall resistance measurements provide clear evidence for a band realignment that is accompanied by a transfer of electrons originally occupying the graphene's spin degenerate Dirac cones into -RuCl 3 band states with in-plane spin polarization. Left behind are holes in two separate Fermi pockets, only the dispersion of one of which is distorted near the Fermi energy due to spin selective hybridization with these spin polarized -RuCl 3 band states. This interpretation is supported by our DFT calculations. An unexpected damping of the quantum oscillations as well as a zero field resistance upturn close to the Néel temperature of -RuCl 3 suggests the onset of additional spin scattering due to spin fluctuations in the -RuCl 3 .

We report a discovery, through first-principles calculations, that crystalline Ge-Sb-Te ͑GST͒ phase-change materials exhibit the topological insulating property. Our calculations show that the materials become topological insulator or develop conducting surfacelike interface states depending on the layer stacking sequence. It is shown that the conducting interface states originate from topological insulating Sb 2 Te 3 layers in GSTs and can be crucial to the electronic property of the compounds. These interface states are found to be quite resilient to atomic disorders but sensitive to the uniaxial strains. We presented the mechanisms that destroy the topological insulating order in GSTs and investigated the role of Ge migration that is believed to be responsible for the amorphorization of GSTs.Topological insulator ͑TI͒ has a bulk-phase energy gap but contains conducting surface states that have linear energy-momentum dispersions near time-reversal invariant momenta ͑TRIM͒. 1-4 These surface states are chiral and robust to external perturbations because they are protected by time-reversal symmetry. Finding new TI materials and exploring implications to device applications have been the primary focus of current research on TI. 5-8 Also the change in topological insulating property and detailed emergent behaviors of the surface states when the composition and structure of TI are tailored are still yet to be investigated.Phase-change materials such as Ge-Sb-Te ͑GST͒ compounds are considered the best candidates for nextgeneration nonvolatile memories because of their rapid, and reversible cycles between the crystalline and amorphous structures. 9-12 Detailed atomic and electronic structures associated with the structural transition of GST compounds have been extensively studied 13-15 but the mechanism and factors responsible for the very fast atomic rearrangement are still unknown. Nor is the electronic structure of GST understood sufficiently to explain the conducting properties. Movement of Ge atoms from octahedral to tetrahedral sites has been proposed as the mechanism of structural transitions from metastable rocksalt or stable hexagonal structures to nonconducting amorphous phase. 11,13 Several candidate models have been suggested for ͑meta-͒ stable crystalline phases. Petrov proposed the layer sequence of Te-Sb-Te-Ge-Te-Te-Ge-Te-Sb ͑Ref. 16͒ ͑the Petrov sequence͒. Kooi and De Hosson ͑KH͒ proposed a different layer sequence of Te-Ge-Te-Sb-Te-Te-Sb-Te-Ge ͑Ref. 17͒ ͑the KH sequence͒. In firstprinciples calculations, the Petrov sequence is slightly less stable than the KH sequence. 18 GeTe and Sb 2 Te 3 are the main components of GSTs ͑Refs. 11, 12, and 19͒ and have finite band gaps in the bulk phase. Sb 2 Te 3 is topological insulator that has gapless edge states protected by time-reversal symmetry while maintaining bulk energy gap. 20,21 GeTe does not have such properties. For gapless edge states to exist, strong spin-orbit coupling ͑SOC͒ is needed to produce a parity inversion at TRIM. 4,20 Since the crystallin...