Ab-initio transport across Bismuth Selenide surface barriers

We investigate the effect of potential barriers in the form of step edges on the scattering properties of Bi$_2$Se$_3$(111) topological surface states by means of large-scale ab-initio transport simulations. Our results demonstrate the suppression of perfect backscattering, while all other scattering processes, which do not entail a complete spin and momentum reversal, are allowed. Furthermore, we find that the spin of the surface state develops an out of plane component as it traverses the barrier. Our calculations reveal the existence of quasi-bound states in the vicinity of the surface barriers, which appear in the form of an enhanced density of states in the energy window corresponding to the topological state. For double barriers we demonstrate the formation of quantum well states. To complement our first-principles results we construct a two-dimensional low-energy effective model and show that band bending plays a significant role in the scattering process. Our findings are discussed in the context of a number of recent experimental works.Comment: Updated text, published versio

Oxygen doping and polaron magnetic coupling in Alq3_3 films

The understanding of the Physics underlying the performances of organic spin-valve devices is still incomplete. According to some recent models, spin transport takes place in an impurity band inside the fundamental gap of organic semiconductors. This seems to be confirmed by recent experiments performed with La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/AlO$_x$/Co devices. The reported results suggest a possible correlation between the magnetoresistance and the variable oxygen doping in the Alq$_3$ spacer. In this paper we investigate by means of first-principles calculations the electronic and magnetic properties of O$_2$ molecules and ions in Alq$_3$ films to establish whether oxygen plays any important role for spin transport in La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/AlO$_x$/Co devices. The conclusion is that it does not. In fact, we show that O$_2$ molecules do not form an impurity band and there is no magnetic interaction between them. In contrast, we suggest that spin-transport may be enabled by the direct exchange coupling between Alq$_3^-$ ions.Comment: 6 pages, 2 figure

Electron doping and magnetic moment formation in N- and C-doped MgO

The formation of the magnetic moment in C- and N-doped MgO is the result of a delicate interplay between Hund's coupling, hybridization and Jahn-Teller distortion. The balance depends on a number of environmental variables including electron doping. We investigate such a dependence by self-interaction corrected density functional theory and we find that the moment formation is robust with respect to electron doping. In contrast, the local symmetry around the dopant is more fragile and two different geometries can be stabilized. Crucially the magnetic moment is always extremely localized, making any carrier mediated picture of magnetism in d^0 magnets unlikely

Current-induced spin polarization in chiral Tellurium: a first-principles quantum transport study

Te is a naturally p-doped semiconductor with a chiral structure, where an electrical current causes the conduction electrons to become spin polarized parallel to the transport direction. In this paper, we present a comprehensive theoretical study of this effect by employing density functional theory (DFT) combined with the non-equilibrium Green's functions (NEGF) technique for quantum transport. We suggest that the spin polarization can quantitatively be estimated in terms of two complementary quantities, namely the non-equilibrium magnetic moments and the spin current density. The calculated magnetic moments are directly compared with the values from previous theoretical studies obtaining overall consistent results. On the other hand, the inspection of the spin current density provides insights of the magnetotransport properties of the material. Specifically, we predict that the resistance along a Te wire changes when an external magnetic field is applied parallel or antiparallel to the charge current direction. The computed magnetoresistance is however quite small (~ 0.025%). Finally, we show that the description of the current-induced spin polarization in terms of the spin current establishes a straightforward connection with the phenomenon called chiral-induced spin selectivity, recently observed in several nano-junctions

Current-induced spin polarization at metallic surfaces from first-principles

We present the results of first-principles calculations based on density functional theory estimating the magnitude of the current-induced spin polarization (CISP) at the surfaces of the $5d$ transition metals with fcc and bcc crystal structures. We predict that the largest surface CISP occurs for W and Ta, whereas CISP is considerably weaker for Pt and Au surfaces. We then discuss how CISP emerges over a length scale equal to few atomic layers as opposed to the spin accumulation characteristic of the SHE, which is related to the materials' spin diffusion length. Finally, using our estimates for the CISP magnitude, we suggest that the spin density appearing near W surfaces in experiments is mostly due to CISP, whereas that at Pt surfaces stems from the Hall effect

A redox-active radical as an effective nanoelectronic component: stability and electrochemical tunnelling spectroscopy in ionic liquids

A redox-active persistent perchlorotriphenylmethyl (PTM) radical chemically linked to gold exhibits stable electrochemical activity in ionic liquids. Electrochemical tunnelling spectroscopy in this medium demonstrates that the PTM radical shows a highly effective redox-mediated current enhancement, demonstrating its applicability as an active nanometer-scale electronic component.We acknowledge the financial support from the EU projects ACMOL (FET Young Explorers, GA no. 618082), ERC StG 2012-306826 e-GAMES, ITN iSwitch (GA no. 642196), COST Action TD1002, the Swiss National Science Foundation (Grant No. 200020-144471), the Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) with project BE-WELL CTQ2013-40480-R, the Generalitat de Catalunya with project 2014-SGR-17, and the Severo Ochoa program. N. C acknowledges the RyC program. C. F. is enrolled in the Materials Science PhD program of UAB. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). Editoria

ERAS in General Thoracic Surgery

Enhanced recovery after surgery (ERAS®) is a strategy that seeks to reduce patients’ perioperative stress response, thereby reducing potential complications, decreasing hospital length of stay and enabling patients to return more quickly to their baseline functional status. This programme results from the union of several perioperative clinical elements that have individually proved to be beneficial to the patient and have showed, when used together, a synergy that results in a significant outcome improvement. The term was coined at the end of the 1990s and originally used to refer to a complex fast-track programme in open colorectal surgery. Subsequently, the practice has spread to other surgical specialties centralising the interest of clinicians and researchers. The objective of this chapter is to analyse the key elements of an ERAS protocol applicable to minimally invasive thoracic surgery

A theoretical perspective on the modification of the magnetocrystalline anisotropy at molecule-cobalt interfaces

We study the modification of the magnetocrystalline anisotropy (MCA) of Co slabs induced by several different conjugated molecular overlayers, i.e., benzene, cyclooctatetraene, naphthalene, pyrene and coronene. We perform first-principles calculations based on Density Functional Theory and the magnetic force theorem. Our results indicate that molecular adsorption tends to favour a perpendicular MCA at surfaces. A detailed analysis of various atom-resolved quantities, accompanied by an elementary model, demonstrates that the underlying physical mechanism is related to the metal-molecule interfacial hybridization and, in particular, to the chemical bonding between the molecular C $p_z$ and the out-of-plane Co $d_{z^2}$ orbitals. This effect can be estimated from the orbital magnetic moment of the surface Co atoms, a microscopic observable accessible to both theory and experiments. As such, we suggest a way to directly assess the MCA modifications at molecule-decorated surfaces, overcoming the limitations of experimental studies that rely on fits of magnetization hysteresis loops. Finally, we also study the interface between Co and both C$_{60}$ and Alq$_3$, two molecules that find widespread use in organic spintronics. We show that the modification of the surface Co MCA is similar upon adsorption of these two molecules, thereby confirming the results of recent experiments.Comment: 10 figures in main text and 3 in the SM, 20 page