12 research outputs found
Taming the resistive switching in Fe/MgO/V/Fe magnetic tunnel junctions: An ab initio study
A possible mechanism for the resistive switching observed experimentally in
Fe/MgO/V/Fe junctions is presented. Ab initio total energy calculations within
the local density approximation and pseudopotential theory shows that by moving
the oxygen ions across the MgO/V interface one obtains a metastable state. It
is argued that this state can be reached by applying an electric field across
the interface. In addition, the ground state and the metastable state show
different electric conductances. The latter results are discussed in terms of
the changes of the density of states at the Fermi level and the charge transfer
at the interface due to the oxygen ion motion
Majorana bound states in open quasi-1D and 2D systems with transverse Rashba coupling
We study the formation of Majorana states in quasi-1D and 2D square lattices
with open boundary conditions, with general anisotropic Rashba coupling, in the
presence of an applied Zeeman field and in the proximity of a superconductor.
For systems in which the length of the system is very large (quasi-1D) we
calculate analytically the exact topological invariant, and we find a rich
phase diagram which is strongly dependent on the width of the system. We
compare our results with previous results based on a few-band approximation. We
also investigate numerically open 2D systems of finite length in both
directions. We use the recently introduced generalized Majorana polarization,
which can locally evaluate the Majorana character of a given state. We find
that the formation of Majoranas depends strongly on the geometry of the system
and if the length and the width are comparable no Majorana states can form,
however, one can show the formation of "quasi-Majorana" states that have a
local Majorana character, but no global Majorana symmetry.Comment: 12 pages, 13 figure
Kondo effect in transport through molecules adsorbed on metal surfaces: from Fano dips to Kondo peaks
The Kondo effect observed in recent STM experiments on transport through CoPc
and TBrPP-Co molecules adsorbed on Au(111) and Cu(111) surfaces, respectively,
is discussed within the framework of a simple model (Phys. Rev. Lett. {\bf 97},
076806 (2006)). It is shown that, in the Kondo regime and by varying the
adequate model parameters, it is possible to produce a crossover from a
conductance Kondo peak (CoPc) to a conductance Fano dip (TBrPP-Co). In the case
of TBrPP-Co/Cu(111) we show that the model reproduces the changes in the shape
of the Fano dip, the raising of the Kondo temperature and shifting to higher
energies of the dip minimum when the number of nearest neighbors molecules is
lowered. These features are in line with experimental observations indicating
that our simple model contains the essential physics underlying the transport
properties of such complex molecules.Comment: 4 pages, 3 figures, submitted to PR
Flat Majorana bands in 2-d lattices with inhomogeneous magnetic fields: topology and stability
In this paper we show that for a range of configurations of inhomogeneous
magnetic fields it is possible to create flat bands of Majorana states
localized on the edges of 2-d lattices. Majorana bound states have been
predicted to exist in both one dimensional and two dimensional systems with
Rashba spin-orbit coupling, magnetic fields, and placed in proximity to a
superconductor. For the proposed systems we present the bulk topological phase
diagrams, and we study the conditions for weak topology which predicts the
formation of bands of Majorana states. The Majorana bands are demonstrated to
be relatively stable with respect to a variety of different perturbations on
both square and hexagonal lattices.Comment: 13 pages, 17 figure
Signature of a topological phase transition in long SN junctions in the spin-polarized density of states
7 pages, 8 figuresInternational audienceWe investigate the spin texture of Andreev bound states and Majorana states in long SN junctions. We show that measuring the spin-polarized density of states (SPDOS) allows one to identify the topological transition. In particular, we find that its total component parallel to the wire is non-zero in the topological phase for the lowest-energy state, while vanishing in the trivial one. Also, the component parallel to the Zeeman field is symmetric between positive and negative energies in the topological phase and asymmetric in the trivial phase. Moreover the SPDOS exhibits a moderate accumulation close to the SN boundary which changes sign when crossing the topological transition. We propose that these signatures may allow one to unambiguously test the formation of a topological phase via spin-resolved transport and STM measurements