Erratum: Competition between covalent bonding and charge transfer at complex-oxide interfaces [Physical Review Letters (2014) 112 (196802)]

Corrección de erratas del artículo "Competition between Covalent Bonding and Charge Transfer at Complex-Oxide Interfaces" (Juan Salafranca, Julián Rincón Javier Tornos, Carlos León, Jacobo Santamaria, Elbio Dagotto,Stephen J. Pennycook, Maria Varela)[Phys. Rev. Lett. 112, 196802 (2014)]Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

SmartFIS: utilizando los teléfonos móviles en el aprendizaje de la Física

El Objetivo General del Proyecto de Innovación “SmartFis” se centraba en facilitar el aprendizaje de los contenidos propios de las múltiples asignaturas impartidas en el Laboratorio de Física General de la Facultad de Ciencias Físicas, en varias titulaciones, mediante la utilización de nuevos recursos didácticos, desarrollando nuevas prácticas de laboratorio basadas en el uso de smartphones, nuevos métodos docentes de laboratorio, y nuevos recursos en el Campus Virtual UCM

Ferroionic inversion of spin polarization in a spin-memristor

Magnetoelectric coupling in artificial multiferroic interfaces can be drastically affected by the switching of oxygen vacancies and by the inversion of the ferroelectric polarization. Disentangling both effects is of major importance toward exploiting these effects in practical spintronic or spinorbitronic devices. We report on the independent control of ferroelectric and oxygen vacancy switching in multiferroic tunnel junctions with a La_(0.7)Sr_(0.3)MnO_3 bottom electrode, a BaTiO_3 ferroelectric barrier, and a Ni top electrode. We show that the concurrence of interface oxidation and ferroelectric switching allows for the controlled inversion of the interface spin polarization. Moreover, we show the possibility of a spin-memristor where the controlled oxidation of the interface allows for a continuum of memresistance states in the tunneling magnetoresistance. These results signal interesting new avenues toward neuromorphic devices where, as in practical neurons, the electronic response is controlled by electrochemical degrees of freedom

Controlled sign reversal of electroresistance in oxide tunnel junctions by electrochemical-ferroelectric coupling

The persistence of ferroelectricity in ultrathin layers relies critically on screening or compensation of polarization charges which otherwise destabilize the ferroelectric state. At surfaces, charged defects play a crucial role in the screening mechanism triggering novel mixed electrochemical-ferroelectric states. At interfaces, however, the coupling between ferroelectric and electrochemical states has remained unexplored. Here, we make use of the dynamic formation of the oxygen vacancy profile in the nanometerthick barrier of a ferroelectric tunnel junction to demonstrate the interplay between electrochemical and ferroelectric degrees of freedom at an oxide interface. We fabricate ferroelectric tunnel junctions with a La_0.7Sr_0.3MnO_3 bottom electrode and BaTiO_3 ferroelectric barrier. We use poling strategies to promote the generation and transport of oxygen vacancies at the metallic top electrode. Generated oxygen vacancies control the stability of the ferroelectric polarization and modify its coercive fields. The ferroelectric polarization, in turn, controls the ionization of oxygen vacancies well above the limits of thermodynamic equilibrium, triggering the build up of a Schottky barrier at the interface which can be turned on and off with ferroelectric switching. This interplay between electronic and electrochemical degrees of freedom yields very large values of the electroresistance (more than 10^6% at low temperatures) and enables a controlled switching between clockwise and counterclockwise switching modes in the same junction (and consequently, a change of the sign of the electroresistance). The strong coupling found between electrochemical and electronic degrees of freedom sheds light on the growing debate between resistive and ferroelectric switching in ferroelectric tunnel junctions, and moreover, can be the source of novel concepts in memory devices and neuromorphie computing

Resistive switching in manganite/graphene hybrid planar nanostructures

We report on the fabrication and magnetotransport characterization of hybrid graphene-based nanodevices with epitaxial nanopatterned La_(0.7)Sr_(0.3)MnO_(3) manganite electrodes grown on SrTiO_(3)(100). The few-layer graphene was deposited onto the predefined manganite nanowires by using a mechanical transfer technique. These nanodevices exhibit resistive switching and hysteretic transport as measured by current-voltage curves. The resistance can be reversibly switched between high and low states, yielding a consistent non-volatile memory response. The effect is discussed in terms of changes in the concentration of oxygen vacancies at the space charge region of the Schottky barriers building at the contacts

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Symmetrical interfacial reconstruction and magnetism in La0.7Ca0.3MnO3/YBa2Cu3O7/La0.7Ca0.3MnO3 heterostructures

Artículo firmado por 15 autoresWe have analyzed the interface structure and composition of La0.7Ca0.3MnO3/YBa2Cu3O7/La0.7Ca0.3MnO3 trilayers by combined polarized neutron reflectometry, aberration-corrected microscopy, and atomic column resolution electron-energy-loss spectroscopy and x-ray absorption with polarization analysis. We find the same stacking sequence at both top and bottom cuprate interfaces. X-ray magnetic circular dichroism experiments show that both cuprate interfaces are magnetic with a magnetic moment induced in Cu atoms as expected from symmetric Mn-O-Cu superexchange paths. These results supply a solid footing for the applicability of recent theories explaining the interplay between magnetism and superconductivity in this system in terms of the induced Cu spin polarization at both interfaces [J. Salafranca and S. Okamoto, Phys. Rev. Lett. 105, 256804 (2010)].Ministerio de Ciencia e Innovación (España)Consejo Europeo de Investigación (ERC)United States Department of Energy (DOE)Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

Equal-spin Andreev reflection and long range coherent transport in hightemperature superconductor/half-metallic ferromagnet junctions

Está depositada la versión postprint del artículoConventional superconductivity is incompatible with ferromagnetism, because the magnetic exchange field tends to spin-polarize electrons and breaks apart the opposite-spin singlet Cooper pairs(1). Yet, the possibility of a long-range penetration of superconducting correlations into strong ferromagnets has been evinced by experiments that found Josephson coupling between superconducting electrodes separated afar by a ferromagnetic spacer(2-7). This is considered a proof of the emergence at the superconductor/ferromagnetic (S/F) interfaces of equal-spin triplet pairing, which is immune to the exchange field and can therefore propagate over long distances into the F (ref. 8). This effect bears much fundamental interest and potential for spintronic applications(9). However, a spectroscopic signature of the underlying microscopic mechanisms has remained elusive. Here we do show this type of evidence, notably in a S/F system for which the possible appearance of equal-spin triplet pairing is controversial(10-12): heterostructures that combine a half-metallic F (La0.7Ca0.3MnO3) with a d-wave S (YBa2Cu3O7). We found quasiparticle and electron interference effects in the conductance across the S/F interfaces that directly demonstrate the long-range propagation across La0.7Ca0.3MnO3 of superconducting correlations, and imply the occurrence of unconventional equal-spin Andreev reflection. This allows for an understanding of the unusual proximity behaviour observed in this type of heterostructures(12,13).Agence Nationale de la Recherche (ANR)RTRA grant 'Supraspin'Union Europea (Programa FP 7)Ministerio de Ciencia e Innovación (España)Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

Characterization of surface metallic states in SrTiO_(3) by means of aberration corrected electron microscopy

El texto completo de este trabajo no se encuentra disponible por no haber sido facilitado aún por su autor, por restricciones de copyright, o por no existir una versión digitalAn unusual conducting surface state can be produced in SrTiO3 substrates by irradiation with Argon ions from a plasma source, at low energy and high doses. The effects of irradiation are analyzed here by atomic force microscopy (AFM) and aberration corrected scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). Depth sensitive studies demonstrate the existence of a heavily damaged surface layer and an oxygen vacancy rich layer immediately underneath, both induced during the irradiation process. We find a clear dependence of the Ti oxidation state with the depth, with a very intense Ti3+ component near the surface. Oxygen vacancies act as n-type doping by releasing electrons into the lattice and producing an insulator-to-metal transition, which explains the unusual metallic behavior of these samples.Materials Sciences and Engineering Division of the US Department of Energy (DOE)ORNL’s Shared Research Equipment (ShaRE) User ProgramERC starting Investigator AwardDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

Interface magnetism in La0.7Ca0.3MnO3/PrBa2Cu3O7 epitaxial heterostructures

All oxide magnetic tunnel junctions based on epitaxial La0.7Ca0.3MnO3 (LCMO)(8nm)/PrBa2Cu3O7 (PBCO) (3-8nm)/LCMO(25-50nm) heterostructures grown on (100) SrTiO3 are examined. Manganite electrodes show large (bulk-like) magnetic moments and exhibit different magnetic anisotropies with different easy axes directions. A form of low dimensional magnetism is induced at the interfaces by the superexchange interaction across the reconstructed bonds. It acts as an exchange spring, driving ferromagnetic coupling between the electrodes. Resistance versus magnetic field loops demonstrate that the interfacial coupling strength depends on electric field through its effect on electronic reconstruction and orbital hierarchy at the interface. The electrically controlled magnetic coupling between the magnetic moments of the electrodes signals a new path toward low dissipation spintronics.Ministerio de Economía y Competitividad (España)Comunidad de MadridDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu