Spin-orbit proximity effect in graphene on metallic substrates: decoration vs intercalation with metal adatoms

The so-called spin-orbit proximity effect experimentally realized in graphene (G) on several different heavy metal surfaces opens a new perspective to engineer the spin-orbit coupling (SOC) for new generation spintronics devices. Here, via large-scale density functional theory (DFT) calculations performed for two distinct graphene/metal models, G/Pt(111) and G/Au/Ni(111), we show that the spin-orbit splitting of the Dirac cones (DCs) in these stuctures might be enhanced by either adsorption of adatoms on top of graphene (decoration) or between the graphene and the metal (intercalation). While the decoration by inducing strong graphene-adatom interaction suppresses the linearity of the G's $\pi$ bands, the intercalated structures reveal a weaker adatom-mediated graphene/substrate hybridization which preserves well-defined although broadened DCs. Remarkably, the intercalated G/Pt(111) structure exhibits splittings considerably larger than the defect-free case

Fe/GeTe(111) heterostructures as an avenue towards 'ferroelectric Rashba semiconductors'-based spintronics

By performing density functional theory (DFT) and Green's functions calculations, complemented by X-ray Photoemission Spectroscopy, we investigate the electronic structure of Fe/GeTe(111), a prototypical ferromagnetic/Rashba-ferroelectric interface. We reveal that such system exhibits several intriguing properties resulting from the complex interplay of exchange interaction, electric polarization and spin-orbit coupling. Despite a rather strong interfacial hybridization between Fe and GeTe bands, resulting in a complete suppression of the surface states of the latter, the bulk Rashba bands are hardly altered by the ferromagnetic overlayer. This could have a deep impact on spin dependent phenomena observed at this interface, such as spin-to-charge interconversion, which are likely to involve bulk rather than surface Rashba states.Comment: 8 pages, 4 figure

Giant spin Hall Effect in two-dimensional monochalcogenides

One of the most exciting properties of two dimensional materials is their sensitivity to external tuning of the electronic properties, for example via electric field or strain. Recently discovered analogues of phosphorene, group-IV monochalcogenides (MX with M = Ge, Sn and X = S, Se, Te), display several interesting phenomena intimately related to the in-plane strain, such as giant piezoelectricity and multiferroicity, which combine ferroelastic and ferroelectric properties. Here, using calculations from first principles, we reveal for the first time giant intrinsic spin Hall conductivities (SHC) in these materials. In particular, we show that the SHC resonances can be easily tuned by combination of strain and doping and, in some cases, strain can be used to induce semiconductor to metal transitions that make a giant spin Hall effect possible even in absence of doping. Our results indicate a new route for the design of highly tunable spintronics devices based on two-dimensional materials

Advanced modeling of materials with PAOFLOW 2.0:New features and software design

Recent research in materials science opens exciting perspectives to design novel quantum materials and devices, but it calls for quantitative predictions of properties which are not accessible in standard first principles packages. PAOFLOW, is a software tool that constructs tight-binding Hamiltonians from self consistent electronic wavefunctions by projecting onto a set of atomic orbitals. The electronic structure provides numerous materials properties that otherwise would have to be calculated via phenomenological models. In this paper, we describe recent re-design of the code as well as the new features and improvements in performance. In particular, we have implemented symmetry operations for unfolding equivalent k-points, which drastically reduces the runtime requirements of first principles calculations, and we have provided internal routines of projections onto atomic orbitals enabling generation of real space atomic orbitals. Moreover, we have included models for non-constant relaxation time in electronic transport calculations, doubling the real space dimensions of the Hamiltonian as well as the construction of Hamiltonians directly from analytical models. Importantly, PAOFLOW has been now converted into a Python package, and is streamlined for use directly within other Python codes. The new object oriented design treats PAOFLOW's computational routines as class methods, providing an API for explicit control of each calculation.</p

Ferroelectric control of charge-to-spin conversion in WTe2

This dataset contains the Quantum Espresso input files of both bilayer and bulk ferroelectric structures of WTe2 from which all figures inside the paper can be reproduced

Ab initio study of the relationship between spontaneous polarization and p-type doping in quasi-freestanding graphene on H-passivated SiC surfaces

The recent proposal of a direct equivalence between the p-type doping typically found in quasi-free-standing graphene (QFG) obtained on H-passivated silicon carbide surface and the spontaneous polarization (SP) associated to the particular SiC polytype, opens the possibility of tuning the number of carriers in the Dirac cones without the need of external gate voltages. However, first-principles calculations which could confirm at the atomic scale the effect of the SP are lacking mainly due to the difficulty of combining a bulk property such as the SP with the surface confined graphene doping. Here we develop an approach based on standard density functional theory (DFT) calculations in order to quantify the effect of the SP on the QFG’s doping level. To this end, a double gold layer is attached at the C-terminated bottom of the slab which introduces a metal-induced gap state that pins the chemical potential inside the gap thus allowing a meaningful comparison of the QFG’s dopings among different polytypes. Our model is generalized by performing large-scale DFT calculations where self-doping in the QFG is included via point defects in order to estimate the interplay between both sources of p-type doping (SP- versus defect-induced) which turns out to be essentially additive.This work was supported by the Spanish Ministry of Innovation and Science under contract Nos. MAT2013-47878-C2-R and MAT2012-38045-C04-04. J.S. acknowledges Polish Ministry of Science and Higher Education for financing the postdoctoral stay at the ICMM-CSIC in the frame of the program Mobility Plus

Ferroelectric control of charge-to-spin conversion in WTe2

This dataset contains the Quantum Espresso input files of both bilayer and bulk ferroelectric structures of WTe2 from which all figures inside the paper can be reproduced