Spin transport in dangling-bond wires on doped H-passivated Si(100)

New advances in single-atom manipulation are leading to the creation of atomic structures on H passivated Si surfaces with functionalities important for the development of atomic and molecular based technologies. We perform total-energy and electron-transport calculations to reveal the properties and understand the features of atomic wires crafted by H removal from the surface. The presence of dopants radically change the wire properties. Our calculations show that dopants have a tendency to approach the dangling-bond wires, and in these conditions, transport is enhanced and spin selective. These results have important implications in the development of atomic-scale spintronics showing that boron, and to a lesser extent phosphorous, convert the wires in high-quality spin filters.Comment: 11 pages, 4 figure

Electronic surface states and dielectric self-energy profiles in colloidal nanoscale platelets of CdSe

International audienceThe electronic surface states and dielectric self-energy profiles in CdSe colloidal nanoscale platelets are explored by means of an original ab initio approach. In particular, we show how the different coatings deeply modify the quantum and dielectric confinement in CdSe nanoscale platelets. Molecular coating leads to an electronic band gap free of electronic surface states as well as an optimal surface coverage. The reduced blinking in CdSe nanoscale platelets is discussed. The theoretical method here proposed allows one to go beyond the popular empirical description of abrupt dielectric interfaces by explicitly describing the nanoplatelet surface morphology and polarisability at the atomic level. This theoretical study open the way toward more precise description of the dielectric confinement effect in any hybrid system exhibiting 2D electronic properties

Rashba and Dresselhaus Effects in Hybrid Organic-Inorganic Perovskites: From Basics to Devices

J.E. and C.K. thank R. Winkler for fruitful discussions. We gratefully acknowledge Prof. R.-G.Xiong for providing Bz2PbCl4 crystallographic data.International audienceWe use symmetry analysis, density functional theory calculations, and k·p modeling to scrutinize Rashba and Dresselhaus effects in hybrid organic-inorganic halide perovskites. These perovskites are at the center of a recent revolution in the field of photovoltaics but have also demonstrated potential for optoelectronic applications such as transistors and light emitters. Due to a large spin-orbit coupling of the most frequently used metals, they are also predicted to offer a promising avenue for spin-based applications. With an in-depth inspection of the electronic structures and bulk lattice symmetries of a variety of systems, we analyze the origin of the spin splitting in two- and three-dimensional hybrid perovskites. It is shown that low-dimensional nanostructures made of CH3NH3PbX3 (X = I, Br) lead to spin splittings that can be controlled by an applied electric field. These findings further open the door for a perovskite-based spintronics

Solid-State Physics Perspective on Hybrid Perovskite Semiconductors

International audienceIn this review we examine recent theoretical investigations on 2D and 3D hybrid perovskites (HOP) that combine classical solid-state physics concepts and density functional theory (DFT) simulations as a tool for studying their optoelectronic properties. Such an approach allows one to define a new class of semiconductors, where the pseudocubic high temperature perovskite structure plays a central role. Bloch states and k.p Hamiltonians yield new insight into the influence of lattice distortions, including loss of inversion symmetry, as well as spin-orbit coupling. Electronic band folding and degeneracy, effective masses and optical absorption are analyzed. Concepts of Bloch and envelope functions, as well as confinement potential are discussed in the context of layered HOP and 3D HOP heterostructures. Screening and dielectric confinements are important for room temperature optical properties of 3D and layered HOP, respectively. Non-radiative Auger effects are analyzed for the first time close to the electronic band gap of 3D hybrid perovskites

Elastic transport through dangling-bond silicon wires on H passivated Si(100)

We evaluate the electron transmission through a dangling-bond wire on Si(100)-H (2x1). Finite wires are modelled by decoupling semi-infinite Si electrodes from the dangling-bond wire with passivating H atoms. The calculations are performed using density functional theory in a non-periodic geometry along the conduction direction. We also use Wannier functions to analyze our results and to build an effective tight-binding Hamiltonian that gives us enhanced insight in the electron scattering processes. We evaluate the transmission to the different solutions that are possible for the dangling-bond wires: Jahn-Teller distorted ones, as well as antiferromagnetic and ferromagnetic ones. The discretization of the electronic structure of the wires due to their finite size leads to interesting transmission properties that are fingerprints of the wire nature

Advances and promises of layered halide hybrid perovskite semiconductors

Layered halide hybrid organic-inorganic perovskites (HOP) have been the subject of intense investigation before the rise of three-dimensional (3D) HOP and their impressive performance in solar cells. Recently, layered HOP have also been proposed as attractive alternatives for photostable solar cells and revisited for light-emitting devices. In this review, we combine classical solid-state physics concepts with simulation tools based on density functional theory to overview the main features of the optoelectronic properties of layered HOP. A detailed comparison between layered and 3D HOP is performed to highlight differences and similarities. In the same way as the cubic phase was established for 3D HOP, here we introduce the tetragonal phase with D symmetry as the reference phase for 2D monolayered HOP. It allows for detailed analysis of the spin-orbit coupling effects and structural transitions with corresponding electronic band folding. We further investigate the effects of octahedral tilting on the band gap, loss of inversion symmetry and possible Rashba effect, quantum confinement, and dielectric confinement related to the organic barrier, up to excitonic properties. Altogether, this paper aims to provide an interpretive and predictive framework for 3D and 2D layered HOP optoelectronic properties.The work at FOTON is supported by Agence Nationale pour la Recherche (SNAP and SuperSansPlomb projects) and was performed using HPC resources from GENCI-CINES/IDRIS Grant 2016-c2012096724. The work at ISCR is supported by Agence Nationale pour la Recherche (TRANSHYPERO project). J.E.’s work is supported by the Fondation d’entreprises banque Populaire de l’Ouest under Grant PEROPHOT 2015. The work at Los Alamos National Laboratory (LANL) was supported by LANL LDRD program and was partially performed at the Center for Nonlinear Studies and at the Center for Integrated Nanotechnologies, a U.S. Department of Energy, Office of Science user facility. The Groningen team would like to acknowledge funding from European Research Council (ERC Starting Grant “Hy-SPOD” No. 306983) and by the Foundation for Fundamental Research on Matter (FOM), which is part of The Netherlands Organization for Scientific Research (NWO), under the framework of the FOM Focus Group “Next Generation Organic Photovoltaics”. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295). This project received funding from the European Union's Horizon 2020 research and innovation programme under the grant agreement no. 687008.Peer Reviewe

Cover Picture: Giant spin–orbit coupling in halide perovskites opens the door to spintronics and spin–orbitronics. (J. Phys. Chem. Lett. 8(14), 2017)

The Journal of Physical Chemistry Letters 8(14) cover picture (ACS Publication / e-ISSN: 1948-7185

Inspections ab initio des hystereses magnetiques et redox

Les systèmes bistables connaissent un intérêt croissant motivé, entre autres, par la perspective d'applications en électronique moléculaire. Parmi ces systèmes certains possèdent la capacité d'exister sous deux états électroniques dans les mêmes conditions, Le. présentant une hystérèse. Deux propriétés sont couramment associées à l'hystérèse, le magnétisme et l'activité rédox. Si ces phénomènes sont connus de longues dates, des zones d'ombre demeurent dans leur mécanisme. Par l'application de calculs ab initio basés sur la fonction d'onde, l'objet de ce travail est de dégager les phénomènes physiques sous-jacents à l'ouverture de boucle d'hystérésis dans les composés à transition de spin (bistabilité magnétique) et dans des complexes de porphyrine (bistabilité rédox). Les ingrédients microscopiques ainsi récoltés sont utilisés pour remonter au comportement macroscopique des matériaux par le biais de modèles thermodynamiques ou de hamiltoniens modèles.Bistable systems are more and more present; part of the reason is to be found in the possible applications in molecular electronics. Sorne of those systems can exist under two different electronic states under the same conditions. As a consequence its present an hysteresis. Two properties are commonly associated with the hysteresis response, magnetism and redox activity. Even though these phenomena are not new, parts of the mechanisms remains unknown. Thanks to wavefunction-based ab initio calculations, this work aims at shedding sorne light on the physics behind the hysteretic behavior in spin-crossover compounds (magnetic bistability) and porphyrin-based complexes (redox bistability). These previous microscopie elements are then collect into thermodynamic models or model Hamiltonian in order to retrieve the macroscopic behaviour of the materials.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF