CSIC - Institute of Materials Science

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Ricote J.,CSIC - Institute of Materials Science
Nature Nanotechnology | Year: 2017

The peculiar features of domain walls observed in ferroelectrics make them promising active elements for next-generation non-volatile memories, logic gates and energy-harvesting devices. Although extensive research activity has been devoted recently to making full use of this technological potential, concrete realizations of working nanodevices exploiting these functional properties are yet to be demonstrated. Here, we fabricate a multiferroic tunnel junction based on ferromagnetic La0.7Sr0.3MnO3 electrodes separated by an ultrathin ferroelectric BaTiO3 tunnel barrier, where a head-to-head domain wall is constrained. An electron gas stabilized by oxygen vacancies is confined within the domain wall, displaying discrete quantum-well energy levels. These states assist resonant electron tunnelling processes across the barrier, leading to strong quantum oscillations of the electrical conductance. © 2017 Nature Publishing Group

Guinea F.,CSIC - Institute of Materials Science | Katsnelson M.I.,Radboud University Nijmegen | Geim A.K.,University of Manchester
Nature Physics | Year: 2010

Among many remarkable qualities of graphene, its electronic properties attract particular interest owing to the chiral character of the charge carriers, which leads to such unusual phenomena as metallic conductivity in the limit of no carriers and the half-integer quantum Hall effect observable even at room temperature. Because graphene is only one atom thick, it is also amenable to external influences, including mechanical deformation. The latter offers a tempting prospect of controlling graphenes properties by strain and, recently, several reports have examined graphene under uniaxial deformation. Although the strain can induce additional Raman features, no significant changes in graphenes band structure have been either observed or expected for realistic strains of up to ∼15% (refs9, 10, 11). Here we show that a designed strain aligned along three main crystallographic directions induces strong gauge fields that effectively act as a uniform magnetic field exceeding 10 T. For a finite doping, the quantizing field results in an insulating bulk and a pair of countercirculating edge states, similar to the case of a topological insulator. We suggest realistic ways of creating this quantum state and observing the pseudomagnetic quantum Hall effect. We also show that strained superlattices can be used to open significant energy gaps in graphenes electronic spectrum. © 2010 Macmillan Publishers Limited. All rights reserved.

Garcia R.,CSIC - Institute of Materials Science | Knoll A.W.,IBM | Riedo E.,Georgia Institute of Technology
Nature Nanotechnology | Year: 2014

The nanoscale control afforded by scanning probe microscopes has prompted the development of a wide variety of scanning-probe-based patterning methods. Some of these methods have demonstrated a high degree of robustness and patterning capabilities that are unmatched by other lithographic techniques. However, the limited throughput of scanning probe lithography has prevented its exploitation in technological applications. Here, we review the fundamentals of scanning probe lithography and its use in materials science and nanotechnology. We focus on robust methods, such as those based on thermal effects, chemical reactions and voltage-induced processes, that demonstrate a potential for applications. © 2014 Macmillan Publishers Limited.

Garcia-Frutos E.M.,CSIC - Institute of Materials Science
Journal of Materials Chemistry C | Year: 2013

1D π-conjugated organic micro- or nanostructures keep all the advantages found in organic single crystals, e.g. high crystallinity, but without the tricky growth associated with large-sized crystals. They also present low-cost processing, solution processable materials, and large-area fabrication, and are compatible with flexible substrates. Electronic and optical properties of 1D π-conjugated organic micro- and nanomaterials can be tuned by changing their size at the central core or chemical modification of the aromatic substituents, among other alternatives. Current challenges are to find and develop an accurate control of the morphology, size, degree of uniformity, and alignment of the micro- and nanometer-sized organic single crystals, for future applications in miniaturized devices. © 2013 The Royal Society of Chemistry.

The in situ formation of sub-100 nm solid frameworks stabilized against dissolution by the addition of nanoseeds allows the facile and controllable synthesis of TiO2 (anatase) mesocrystalline structures with spherical shape, mesoporosity and sizes between 50 and 70 nm. As an example of their multifunctionality, these structures show good capabilities for enzyme immobilization and adequate photocatalytic properties. © 2011 The Royal Society of Chemistry.

Fuertes A.,CSIC - Institute of Materials Science
Journal of Materials Chemistry | Year: 2012

Oxynitride perovskites of early transition metals and rare earth or alkaline earth elements have been reported in the last decade as non-toxic pigments, colossal magnetoresistive materials, high permittivity dielectrics and photocatalysts. Nitride and oxide may occupy the same sites in the perovskite structure, forming solid solutions with ratios that are adjusted by synthesis. The valence states of cations, the bond covalency and the energy of the electronic states can be tuned by the introduction of nitrogen as a consequence of its lower electronegativity, higher electronic polarisability and higher formal anion charge relative to oxygen. This feature article will discuss the influence of the above factors on the crystal chemistry and properties of this group of materials that have emerged as a result of the development of new and controlled synthetic methodologies. © 2012 The Royal Society of Chemistry.

Stengel M.,CSIC - Institute of Materials Science
Physical Review Letters | Year: 2011

Macroscopically, confined electron gases at polar oxide interfaces are rationalized within the simple "polar catastrophe" model. At the microscopic level, however, many other effects such as electric fields, structural distortions and quantum-mechanical interactions enter into play. Here, we show how to bridge the gap between these two length scales, by combining the accuracy of first-principles methods with the conceptual simplicity of model Hamiltonian approaches. To demonstrate our strategy, we address the equilibrium distribution of the compensating free carriers at polar LaAlO3/SrTiO3 interfaces. Remarkably, a model including only calculated bulk properties of SrTiO3 and no adjustable parameters accurately reproduces our full first-principles results. Our strategy provides a unified description of charge compensation mechanisms in SrTiO 3-based systems. © 2011 American Physical Society.

Rurali R.,Autonomous University of Barcelona | Rurali R.,CSIC - Institute of Materials Science
Reviews of Modern Physics | Year: 2010

In this Colloquium the theory of silicon nanowires is reviewed. Nanowires with diameters below 10 nm are the focus, where quantum effects become important and the properties diverge significantly from those of bulk silicon. These wires can be treated within electronic structure simulation methods and will be among the most important functional blocks of future nanoelectronic devices. First, the structural properties of silicon nanowires are reviewed, emphasizing the close connection between the growth orientation, the cross section, and the bounding facets. Second, the electronic structure of pristine and doped nanowires is discussed, which holds the ultimate key for their applicability in novel electronic devices. Finally, transport properties are reviewed where some important limitations in the performances of nanowire-based devices can lay. Many unique properties of these systems are at the same time defying challenges and opportunities for technological advances. © 2010 The American Physical Society.

Grushin A.G.,CSIC - Institute of Materials Science
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

In Lorentz violating quantum electrodynamics (QED) it is known that a radiatively induced Chern-Simons term appears in the effective action for the gauge field, which is finite but undetermined. This ambiguity is shown to be absent in a condensed matter realization of such a theory in Weyl semi-metals due to the existence of a full microscopic model from which this effective theory emerges. Physically observable consequences such as birefringence are also discussed in this scenario. © 2012 American Physical Society.

Nieto-Vesperinas M.,CSIC - Institute of Materials Science
Optics Letters | Year: 2015

We establish the equations for the time-averaged optical torque on dipolar bi-isotropic particles. Due to the interference of the scattered fields, it has a term additional to the one that is commonly employed in theory and experiments. Its consequences for conservation of energy, angular momentum, and effects like negative torques are discussed. © 2015 Optical Society of America.

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