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© 2001 The American Physical Society. A. Mu., F. J. G. de A., and J. E. O. are supported by the Universidad del País Vasco (1/UPV/EHU/00057.240-EA-8078/2000) and the Max Planck Research Award Program. V. R. and S. R. are supported by the CNRS-ULTIMATECH program, the CRIF, and the Université de Paris 7. A. Ma. is supported by a Marie Curie Fellowship of the European Union, under Contract No. HPMF-CT-2000-00565. V. P.-D. is supported by the Comunidad Autónoma de Madrid (Project No. 07N/0042/98) and the DEFICIT (Spain) (Grant No. PB-97-1199). The experiments performed at LURE were funded by the Large Scale Facilities program of the European Union. Critical reading of the manuscript by F. J. Himpsel is acknowledged. Technical support from the Spanish-French beam line staff is gratefully acknowledged., STM images show that vicinal Au(788) surfaces are made up or a uniform array of (111)-oriented terraces of similar width (similar to3.8 nm). This uniformity makes it possible to study the electronic Structure of the resulting step superlattice by angle-resolved photoemission. We show that for this terrace array the surface state appears to be broken up into one-dimensional quantum-well levels, indicating total electron confinement within the terraces. The angular resolution allows the probability density of the terrace quantum well state to be mapped in reciprocal space, complementing nicely the wave function measured in real space by STM., Universidad del País Vasco, CNRS-ULTIMATECH, CRIF, Université de Paris 7, Marie Curie Fellowship of the European Union, Comunidad Autónoma de Madrid, DEFICIT (Spain), Max Planck Research Award Program, Large Scale Facilities program of the European Union, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

The static stress needed to depin a 2D edge dislocation, the lower dynamic stress needed to keep it moving, its velocity, and displacement vector profile are calculated from first principles. We use a simplified discrete model whose far field distortion tensor decays algebraically with distance as in the usual elasticity. Dislocation depinning in the strongly overdamped case (including the effect of fluctuations) is analytically described. N parallel edge dislocations whose average interdislocation distance divided by the Burgers vector of a single dislocation is L≫1 can depin a given one if N=O(L). Then a limiting dislocation density can be defined and calculated in simple cases., Depto. de Análisis Matemático y Matemática Aplicada, Fac. de Ciencias Matemáticas, TRUE, pub

© American Physical Society, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 1999 The American Physical Society. This work was financed by DGES (Spain) (Grants No. PB-97-0031 and No. PB-97-1199). We thank the staff of ESRF for experimental support and X. Torrelles, F. Flores, E. Tosatti, and S. Modesti for fruitful discussions. A. M. thanks Eusko Jaurlaritza for financial support., The structure of the low-temperature 3 X 3 surface phase of Pb/Ge(111) has been determined by surface x-ray diffraction experiments. Analysis of the data reveals that the Pb layer exhibits a vertical corrugation of similar to 0.4 Angstrom, affecting also the two top Ge layers. Significant distortions are found down to the third Ge layer. This structural model supports that the 3 X 3 ground state can be best described as a cooperative distortion stabilized by a gain in electronic energy. [S0031-9007(99)08749-9]., DGES (Spain), Eusko Jaurlaritza, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2015 American Physical Society. Artículo firmado por 11 autores. This work was supported by the French Agence Nationale de la Recherche (ANR) under Contract SurMott, No. NT-09-618999, and by Spanish Ministerio de Economía y Competitividad, Project No. MAT2014-59966-R. W. S. and D. G. T. contributed equally to this work., Dynamical phase transitions are a challenge to identify experimentally and describe theoretically. Here, we study a new reconstruction of Sn on silicon and observe a reversible transition where the surface unit cell divides its area by a factor of 4 at 250 °C. This phase transition is explained by the 24-fold degeneracy of the ground state and a novel diffusive mechanism, where four Sn atoms arranged in a snakelike cluster wiggle at the surface exploring collectively the different quantum mechanical ground states., French Agence Nationale de la Recherche (ANR), Ministerio de Economía y Competitividad, Spain, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2010 The American Physical Society. This research was supported by the Ramón y Cajal program (C. E. C.) and by Spanish MICINN through Grants No. FIS-2007-65723 (C. E. C.) and No. MAT- 2008-02626 (G. P.)., A powerful method of manipulating the dynamics of quantum coherent particles is to control the phase of their tunneling. We consider a system of two electrons hopping on a quasi-one- dimensional lattice in the presence of a uniform magnetic field and study the effect of adding a time-periodic driving potential. We show that the dynamical phases produced by the driving can combine with the Aharonov-Bohm phases to give precise control of the localization and dynamics of the particles, even in the presence of strong particle interactions., Ramón y Cajal program (C. E. C.), MICINN, Spain, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 1996 The American Physical Society. We are greatly indebted to Roland Ketzmerick for very useful discussions and detailed calculations as well as for his good manners in science. It is with great pleasure that we thank Angel Sánchez for illuminating conversations. We also thank Victoria Hernández for interesting comments. This work is supported by CICYT under Project No. MAT95-0325., We report on a new class of critical states in the energy spectrum of general Fibonacci systems. By introducing a transfer matrix renormalization technique, we prove that the charge distribution of these states spreads over the whole system, showing transport properties characteristic of electronic extended states. Our analytical method is a first step to find out the link between the spatial structure of critical wave functions and their related transport properties., CICYT, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2000 The American Physical Society. J. E. O. and A. Mu. are supported by the Universidad del País Vasco (UPV057.240-EA197/97 and 026/98)and the Max Planck Research Award Program. E. G. M. and A. Ma. are funded by the Spanish DGES (PB-970031) and the Comunidad de Madrid (07N/0031/1998). Experiments were performed at Hasylab within the TMR Contract ERBFMGECTP950059 and at the SRC, which is supported by the NSF under Award No. DMR-9531009. F. J. H. is funded by NSF DMR-9815416. Helpful discussions with P. M. Echenique, F. J. García de Abajo, and E. V. Chulkov are acknowledged, The Cu(111) surface state has been mapped for vicinal surfaces with variable step densities by angle-resolved photoemission. Using tunable synchrotron radiation to vary the Ic dependence perpendicular to the surface, as well as the k(\\) dependence, we find a switch between two qualitatively different regimes at a miscut of 7 degrees (17 Angstrom terrace width). For larger miscut angles the step modulation of the wave function dominates, and for smaller miscut angles the terrace modulation dominates. These observations resolve an apparent inconsistency between prior photoemission and STM results., Universidad del País Vasco, Spanish DGES, Comunidad de Madrid, TMR Contract, NSF, Max Planck Research Award Program, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

We report on the magnetic coupling of La0.7Sr0.3MnO3 layers through SrTiO3 spacers in La0.7Sr0.3MnO3/SrTiO3 epitaxial heterostructures. Combined aberration-corrected microscopy and electron-energy-loss spectroscopy evidence charge transfer to the empty conduction band of the titanate. Ti d electrons interact via superexchange with Mn, giving rise to a Ti magnetic moment as demonstrated by x-ray magnetic circular dichroism. This induced magnetic moment in the SrTiO3 controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm., MICINN, CAM, U.S. Department of Energy, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2012 American Physical Society. We thank R. Hulet and A. Dalgarno for helpful discussions. This work has been supported by MICINN (Spain) through Grants No. FIS2007-65723 and No. FIS2010-21372 Comunidad de Madrid through MICROSERES grant, Army Research Office with funding from the DARPA OLE program, Harvard-MIT CUA, NSF Grant No. DMR-07-05472, AFOSR Quantum Simulation MURI, AFOSR MURI on Ultracold Molecules, and the ARO-MURI on Atomtronics. One of us (I. Z.) acknowledges support from Real Colegio Complutense at Harvard., We show that antiparallel triplet pairing correlations are generated in superfluids with purely s-wave interactions whenever population imbalance enforces anisotropic Fulde Ferrell (FF) or inhomogeneous Larkin-Ovchinikov (LO) states. These triplet correlations appear in the Cooper pair wave function, while the triplet part of the gap remains zero. The same set of quasiparticle states contributes to the triplet component and to the polarization, thus spatially correlating them. In the LO case, this set forms a narrow band of Andreev states centered on the nodes of the s-wave order parameter. This picture naturally provides a unifying explanation of previous findings that attractive p-wave interaction stabilizes FFLO states. We also study a similar triplet mixing which occurs when a balanced two-component system displays FFLO-type oscillations due to a spin dependent optical lattice. We discuss how this triplet component can be measured in systems of ultracold atoms using a rapid ramp across a p-wave Feshbach resonance. This should provide a smoking gun signature of FFLO states, Comunidad de Madrid, Ministerio de Ciencia e Innovación (MICINN), Real Colegio Complutense en Harvard, Harvard-MIT CUA, Army Research Office, NSF, AFOSR Quantum Simulation MURI, AFOSR MURI on Ultracold Molecules, ARO-MURI on Atomtronics, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society. We acknowledge financial support from MCyT (Spain) under Grants No. MAT2003-08627-C0201 and No. FIS2005-0747. A. M. thanks the program ‘‘Ramón y Cajal.’’ R. C. thanks ‘‘Comunidad de Madrid’’ and ‘‘Fondo Social Europeo.’’ Part of this work was performed at the Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. STM images have been analyzed using WSxM software from Nanotec., We report an investigation on the properties of 0.33 ML of Sn on Ge(111) at temperatures down to 5 K. Low-energy electron diffraction and scanning tunneling microscopy show that the (3 x 3) phase formed at similar to 200 K, reverts to a new (root 3 x root 3)R30 degrees phase below 30 K. The vertical distortion characteristic of the (3 x 3) phase is lost across the phase transition, which is fully reversible. Angle-resolved photoemission experiments show that, concomitantly with the structural phase transition, a metal-insulator phase transition takes place. The (root 3 x root 3)R30 degrees ground state is interpreted as the formation of a Mott insulator for a narrow half-filled band in a two-dimensional triangular lattice., MCyT (Spain), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2008 The American Physical Society. We thank Martin Holthaus for stimulating discussions. This work was funded by the MEC (Spain) through Grant Nos. FIS2004-05120 and FIS2007-65723. C. E. C. was supported by a Ramón y Cajal Fellowship., We study the effect of a strong, oscillating driving field on the dynamics of ultracold boson held in an optical lattice. Modeling the system as a Bose-Hubbard model, we show how the driving field can be used to produce and maintain a coherent atomic current by controlling the phase of the intersite tunneling processes. We investigate both the stroboscopic and time- averaged behavior using Floquet theory, and demonstrate that this procedure provides a stable and precise method of controlling coherent quantum systems., MEC (Spain), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 1999 The American Physical Society. Work in Italy has been supported by the INFM Network “Fisica e Tecnologia dei Semiconduttori III-V” and in Madrid by the CAM under Project No. 07N/0034/1998. E. D. and F. D.-A. thank A. Sánchez for collaboration on these topics during these years., We study the electronic properties of GaAs-AlGaAs superlattices with intentional correlated disorder by means of photoluminescence and vertical de resistance. The results are compared to those obtained in ordered and uncorrelated disordered superlattices. We report the first experimental evidence that spatial correlations inhibit localization of states in disordered low-dimensional systems, as our previous theoretical calculations suggested, in contrast to the earlier belief that all eigenstates are localized., CAM, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2009 The American Physical Society. This work was supported by MICINN (Spain) through Grant No. FIS-2007-65723 and the Ramón y Cajal Program (CEC). The authors thank Ferruccio Renzoni,Tania Monteiro, and Peter Reimann for stimulating discussions., We study the response of a Bose-Einstein condensate to an unbiased periodic driving potential. By controlling the space and time symmetries of the driving we show how a directed current can be induced, producing a coherent quantum ratchet. Weak driving induces a regular behavior, and space and time symmetries must both be broken to produce a current. For strong driving, the behavior becomes chaotic and the resulting effective irreversibility means that it is unnecessary to explicitly break time symmetry. Spatial asymmetry alone is then sufficient to produce the ratchet effect, even in the absence of interactions, and although the system remains completely coherent, MICINN (Spain), Ramón y Cajal Program (CEC), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 1999 The American Physical Society. This work was financed by DGICYT (Spain) (Grants No. PB-97-0031, No. PB-97-1199, and No. PB92–0168C). We thank the European Union (A. M. and E. G. M.) and Eusko Jaurlaritza (A. M.) for financial support., The Sn/Ge(111) interface has been investigated across the 3 x 3 -->, root 3 x root 3 R30 degrees phase transition using core level and valence band photoemission spectroscopies. We find, both above and below the transition, two different components in the Sn 4d core level and a bond splitting in the surface state crossing the Fermi energy. Theoretical calculations show that these two effects are due to the existence of two structurally different kinds of Sn atoms that fluctuate at room temperature between two positions and are stabilized in a 3 x 3 structure at low temperature., DGICYT (Spain), European Union, Eusko Jaurlaritza, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2003 The American Physical Society. V. A. M. acknowledges support from NATO. Work at Madrid was supported by DGI-MCyT (MAT2000-0734). Work at Brazil was supported by CNPq and CAPES (Brazilian research agencies) and FAPEAL (Alagoas State agency)., We study the dynamics of an electron subjected to a uniform electric field within a tight-binding model with long-range-correlated diagonal disorder. The random distribution of site energies is assumed to have a power spectrum S(k)similar to1/k(alpha) with alpha>0. de Moura and Lyra [Phys. Rev. Lett. 81, 3735 (1998)10.1103/Phys. Rev. Lett.81.3735] predicted that this model supports a phase of delocalized states at the band center, separated from localized states by two mobility edges, provided alpha>2. We find clear signatures of Bloch-like oscillations of an initial Gaussian wave packet between the two mobility edges and determine the bandwidth of extended states, in perfect agreement with the zero-field prediction., DGI-MCyT, CNPq, CAPES, FAPEAL, NATO, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2009 The American Physical Society. Travel between Bayreuth and Madrid is supported by the DAAD-MEC joint program Acciones Integradas. Work at Madrid was supported by MEC (Project MOSAICO) and BSCH-UCM (Project No. PR34/07-15916). R. P. A. L. ac knowledges support by MEC through the Juan de la Cierva program and G. Rowlands for helpful discussions. C. G. acknowledges support by DFG and DAAD, and C. M. acknowledges helpful discussions with Y. Gaididei, We investigate Bloch oscillations of interacting cold atoms in a mean-field framework. In general, atom-atom interaction causes dephasing and destroys Bloch oscillations. Here we show that Bloch oscillations are persistent if the interaction is modulated harmonically with suitable frequency and phase. For other modulations, Bloch oscillations are rapidly damped. We explain this behavior in terms of collective coordinates whose Hamiltonian dynamics permits one to predict a whole family of stable solutions. In order to describe also the unstable cases, we carry out a stability analysis for Bogoliubov excitations. Using Floquet theory, we are able to predict the unstable modes as well as their growth rate, found to be in excellent agreement with numerical simulations., MEC, BSCH-UCM, DFG, DAAD, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society. This work was supported by UCM (Program BCSH), MEC (Project No. MAT2003-01533) and CAM (Project No. GR/MAT/0039/2004)., UCM, MEC, CAM, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2008 The American Physical Society. The authors thank J.E. Ortega for providing us the Au(788) sample. Financial support from the Spanish MEC, Project No. MAT2006-13149-C02-01 and from the CAM Projects Nos. CAM-S-0505/PPQ/0316 and GR/ MAT/0632/2004 are gratefully acknowledged. V. N. thanks MEC through No. MAT2003-08627-C02-01., Gold vicinal surfaces (788), with a high density of steps, along with (111) flat surfaces taken as a reference, have been nanoindented and their resulting penetration curves and related defect structure comparatively analyzed by AFM and atomistic simulations. Stepped surfaces are shown to yield at smaller loads than (111) ones in agreement with calculations of the critical resolved shear stress needed to nucleate a dislocation. In the stepped surfaces, a novel intermediate state is identified in which the penetration curves depart from a Hertzian behavior prior to the appearance of pop-ins. This state is shown to result from heterogeneous nucleation at preexisting surface steps of dislocation loops, most of which retract and vanish when the indenter load is removed., Spanish MEC, CAM, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2003 The American Physical Society. V. A. M. acknowledges support from MECyD (Project No. SAB2000-0103). A. R. and F. D-A. were supported by DGI-MCyT (Project No. MAT2000-0734) and CAM (Project No. 07N/0075/2001). G. S. and M. A. M-D. acknowledge support from PGC (Project No. BFM2000-1320-C02-01)., The single-parameter scaling hypothesis predicts the absence of delocalized states for noninteracting quasiparticles in low-dimensional disordered systems. We show analytically, using a supersymmetric method combined with a renormalization group analysis, as well as numerically that extended states may occur in the one- and two-dimensional Anderson model with a nonrandom hopping falling off as some power of the distance between sites. The different size scaling of the bare level spacing and the renormalized magnitude of the disorder seen by the quasiparticles finally results in the delocalization of states at one of the band edges of the quasiparticle energy spectrum., MECyD, DGI-MCyT, CAM, PGC, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2010 The American Physical Society. A. B. and S. B. are supported by the EPSRC. J. G. C. was supported by the QIPIRC. S. B. acknowledges the Royal Society and the Wolfson Foundation. C. E. C. was supported by the MICINN (Spain) through Grant No. FIS- 2007-65723, and the Ramón y Cajal Program. J. H. J. acknowledges support from the UK Ministry of Defence., We exploit the nondissipative dynamics of a pair of electrons in a large square quantum dot to perform singlet-triplet spin measurement through a single charge detection and show how this may be used for entanglement swapping and teleportation. The method is also used to generate the Affleck-Kennedy-LiebTasaki ground state, a further resource for quantum computation. We justify, and derive analytic results for, an effective charge-spin Hamiltonian which is valid over a wide range of parameters and agrees well with exact numerical results of a realistic effective-mass model. Our analysis also indicates that the method is robust to the choice of dot-size and initialization errors, as well as decoherence., MICINN, Spain, EPSRC, UK, QIPIRC, Ramón y Cajal Program, Ministry of Defence, UK, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©2006 The American Physical Society. This work was supported by the EPSRC. We thank Shmuel Fishman and Antonio Garcia-Garcia for helpful comments and advice., The quantum dynamics of atoms subjected to pairs of closely spaced delta kicks from optical potentials are shown to be quite different from the well-known paradigm of quantum chaos, the single delta-kick system. We find the unitary matrix has a new oscillating band structure corresponding to a cellular structure of phase space and observe a spectral signature of a localization-delocalization transition from one cell to several. We find that the eigenstates have localization lengths which scale with a fractional power L similar to h(-0.75) and obtain a regime of near-linear spectral variances which approximate the "critical statistics" relation Sigma(2)(L)similar or equal to chi L approximate to 1/2(1-nu)L, where nu approximate to 0.75 is related to the fractal classical phase-space structure. The origin of the nu approximate to 0.75 exponent is analyzed., EPSRC (UK), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2006 The American Physical Society., We study the time-dependent dynamics of a Bose-Einstein condensate trapped in an optical lattice. Modeling the system as a Bose-Hubbard model, we show how applying a periodic driving field can induce coherent destruction of tunneling. In the low-frequency regime, we obtain the novel result that the destruction of tunneling displays extremely sharp peaks when the driving frequency is resonant with the depth of the trapping potential (‘‘multi-photon resonances’’), which allows the quantum phase transition between the Mott insulator and the superfluid state to be controlled with high precision. We further show how the waveform of the field can be chosen to maximize this effect., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2011 American Physical Society. A. S. acknowledges discussions with I. Gruzberg and V. Kagalovsky and the hospitality of the Universidad Complutense de Madrid, where the major part of the work has been done. A. V. M. and F. D.-A. thank K. Slevin, T. Ohtsuki, and R. Römer for fruitful discus- sions. Part of the calculations were performed at the Aula Sun Cluster and the Clúster de Ca´lculo de Alta Capacidad para Técnicas Físicas, funded by the UCM and the EU under the FEDER program. Work in Madrid was supported by MICINN (Projects Mosaico and MAT2010-17180), We calculate numerically the localization length critical index within the Chalker-Coddington model of the plateau-plateau transitions in the quantum Hall effect. We report a finite-size scaling analysis using both the traditional power-law corrections to the scaling function and the inverse logarithmic ones, which provided a more stable fit resulting in the localization length critical index v = 2.616 +/- 0.014. We observe an increase of the critical exponent v with the system size, which is possibly the origin of discrepancies with early results obtained for smaller systems., UCM, EU-FEDER program, MICINN, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2008 The American Physical Society. We thank J. M. Rojo for fruitful discussions. This work was supported by MEC and CAM (Spain) (Grants No. FIS2006-04552, No. FIS2005-00747, and No. and European Social Fund). Part of this work was performed at the Swiss Light Source, Villigen, Switzerland., High-resolution photoemission of the Sn 4d core level of Sn/Ge(111)-(3x3) resolves three main components in the line shape, which are assigned to each of the three Sn atoms that form the unit cell. The line shape found is in agreement with an initial state picture and supports that the two down atoms are inequivalent. In full agreement with these results, scanning tunnel microscopy images directly show that the two down atoms are at slightly different heights in most of the surface, giving rise to an inequivalent-down-atoms (3x3) structure. These results solve a long-standing controversy on the interpretation of the Sn 4d core-level line shape and the structure of Sn/Ge(111)-(3x3)., MEC (Spain), Comunidad de Madrid, European Social Fund, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2007 The American Physical Society. This research was supported by the EPSRC. The author acknowledges the hospitality of the University of Edinburgh where this work was completed, and thanks Sougato Bose for stimulating conversations., We propose a scheme for producing directed motion in a lattice system by applying a periodic driving potential. By controlling the dynamics by means of the effect known as coherent destruction of tunneling, we demonstrate a novel ratchetlike effect that enables particles to be coherently manipulated and steered without requiring local control. Entanglement between particles can also be controllably generated, which points to the attractive possibility of using this technique for quantum information processing., EPSRC (UK), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2019 American Physical Society This work has been supported by the European Research Council (ERC) Consolidator Grant MINT under the Contract No. 615759. Calculations took advantage of the Occigen machines through the DARI project EPOC No. A0020910084 and of the DECI resource FIONN in Ireland at Irish Centre for High-End Computing (ICHEC) through the PRACE project FiPSCO. J. V. acknowledges technical help from Adam Ralph from ICHEC., In transition-metal perovskites (ABO_3) most physical properties are tunable by structural parameters such as the rotation of the BO_6 octahedra. Examples include the Neel temperature of orthoferrites, the conductivity of mixed-valence manganites, or the band gap of rare-earth scandates. Since oxides often hold large internal electric dipoles and can accommodate heavy elements, they also emerge as prime candidates to display Rashba spin-orbit coupling, through which charge and spin currents may be efficiently interconverted. However, despite a few experimental reports in SrTiO_3-based interface systems, the Rashba interaction has been little studied in these materials, and its interplay with structural distortions remains unknown. In this Letter, we identify a bismuth-based perovskite with a large, electrically switchable Rashba interaction whose amplitude can be controlled by both the ferroelectric polarization and the breathing mode of oxygen octahedra. This particular structural parameter arises from the strongly covalent nature of the Bi-O bonds, reminiscent of the situation in perovskite nickelates. Our results not only provide novel strategies to craft agile spin-charge converters but also highlight the relevance of covalence as a powerful handle to design emerging properties in complex oxides., Unión Europea. FP7, DARI project EPOC, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2019 American Physical Society Artículo firmado por más de once autores. Authors acknowledge received funding from the project Quantox of QuantERA ERA-NET Cofund in Quantum Technologies (Grant Agreement No. 731473) implemented within the European Union's Horizon 2020 Programme. This work was supported by Spanish MINECO through Grants No. MAT2014-52405-C02, No. MAT2017-87134-C02, No. MAT2015-72795-EXP, and by Comunidad de Madrid through S2013/336 MIT-2740. Work at Argonne National Laboratory (PNR experiments and analysis) was supported by the U.S. DOE, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. The neutron scattering experiment was conducted at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Beam time support provided at Alice (BMBF Project No. 05K10PC2) is acknowledged. Financial support for developing and building the PM2-VEKMAG beam line and VEKMAG end station was provided by HZB and BMBF (05K10PC2, 05K10WR1, 05K10KE1), respectively. Steffen Rudorff is acknowledged for technical support. J. S. thanks Scholarship program Alembert funded by the IDEX Paris-Saclay, ANR-11-IDEX-0003-02., The electronic reconstruction occurring at oxide interfaces may be the source of interesting device concepts for future oxide electronics. Among oxide devices, multiferroic tunnel junctions are being actively investigated as they offer the possibility to modulate the junction current by independently controlling the switching of the magnetization of the electrodes and of the ferroelectric polarization of the barrier. In this Letter, we show that the spin reconstruction at the interfaces of a La_0.7Sr_0.3MnO_3/BaTiO_3/La_0.7Sr_0.3MnO_3 multiferroic tunnel junction is the origin of a spin filtering functionality that can be turned on and off by reversing the ferroelectric polarization. The ferroelectrically controlled interface spin filter enables a giant electrical modulation of the tunneling magnetoresistance between values of 10% and 1000%, which could inspire device concepts in oxides-based low dissipation spintronics., Union Europea. H2020, Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Bundesministerium für Bildung und Forschung (BMBF), Université Paris-Saclay, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2018 American Physical Society. We thank Diego Alcala, Daniel Jaschke, and Marie Mclain for their useful discussions. This material is based in part upon work supported by the U.S. National Science Foundation under Grants No. PHY-1520915, No. OAC1740130, the U.S. Air Force Office of Scientific Research Grant No. FA9550-14-1-0287, and the U.K. Engineering and Physical Sciences Research Council (EPSRC) through the “Quantum Science with Ultracold Molecules” Programme (Grant No. EP/P01058X/1). This work was performed in part at the Aspen Center for Physics, which is supported by the U.S. National Science Foundation Grant No. PHY-1607611. This work has also been supported by Spain’s MINECO through Grants No. FIS2010-21372 and No. FIS2013-41716-P. L. D. C. thanks Complutense University for hosting his visit to support the work contained in this Letter. The calculations in this Letter were executed on the high performance computing cluster maintained by the Golden Energy Computing Organization at the Colorado School of Mines., We uncover signatures of quantum chaos in the many-body dynamics of a Bose-Einstein condensate-based quantum ratchet in a toroidal trap. We propose measures including entanglement, condensate depletion, and spreading over a fixed basis in many-body Hilbert space, which quantitatively identify the region in which quantum chaotic many-body dynamics occurs, where random matrix theory is limited or inaccessible. With these tools, we show that many-body quantum chaos is neither highly entangled nor delocalized in the Hilbert space, contrary to conventionally expected signatures of quantum chaos., Ministerio de Economía y Competitividad (MINECO), U.S. National Science Foundation, U.S. Air Force Office of Scientific Research Grant, U.K. Engineering and Physical Sciences Research Council (EPSRC) through the "Quantum Science with Ultracold Molecules" Programme, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2017 American Physical Society. This work was supported by the Spanish MA2014- 56063-C2-1-RT, Severo Ochoa SEV-2015-0496 grant, the RyC-2012–11709 contract of J. G., and the Generalitat de Catalunya (2014 SGR 734) project. Electron microscopy observations at ORNL were supported by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Materials Sciences and Engineering Division. M. S. acknowledges the support of MINECO through Grants No. MAT2016-77100-C2-2-P and No. FIS2013- 48668-C2-2-P and of Generalitat de Catalunya (Grant No. 2014 SGR301). Calculations were performed at the Supercomputing Center of Galicia (CESGA). The authors are also grateful to Nico Dix for his collaboration in the growth of the films. Research at UCM sponsored by Fundación BBVA and Spanish MINECO MAT2015- 66888-C3-3-R., Two basic lattice distortions permeate the structural phase diagram of oxide perovskites: antiferrodistortive (AFD) rotations and tilts of the oxygen octahedral network and polar ferroelectric modes. With some notable exceptions, these two order parameters rarely coexist in a bulk crystal, and understanding their competition is a lively area of active research. Here we demonstrate, by using the LaAlO₃/SrTiO₃ system as a test case, that quantum confinement can be a viable tool to shift the balance between AFD and polar modes and selectively stabilize one of the two phases. By combining scanning transmission electron microscopy (STEM) and first-principles-based models, we find a crossover between a bulklike LaAlO₃ structure where AFD rotations prevail, to a strongly polar state with no AFD tilts at a thickness of approximately three unit cells; therefore, in addition to the celebrated electronic reconstruction, our work unveils a second critical thickness, related not to the electronic properties but to the structural ones. We discuss the implications of these findings, both for the specifics of the LaAlO₃/SrTiO₃ system and for the general quest towards nanoscale control of material properties., Ministerio de Economía y Competitividad (MINECO), Severo Ochoa, Generalitat de Catalunya, U.S. Department of Energy (DOE), Fundación BBVA, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2015 American Physical Society. This work was supported by the French Agence Nationale de la Recherche (ANR) under Contract SurMott, No. NT-09-618999, and by Spanish Ministerio de Economía y Competitividad, Project No. MAT2014-59966-R. W. S. and D. G. T. contributed equally to this work. Articulo firmado por más de 10 autores., Dynamical phase transitions are a challenge to identify experimentally and describe theoretically. Here, we study a new reconstruction of Sn on silicon and observe a reversible transition where the surface unit cell divides its area by a factor of 4 at 250 degrees C. This phase transition is explained by the 24-fold degeneracy of the ground state and a novel diffusive mechanism, where four Sn atoms arranged in a snakelike cluster wiggle at the surface exploring collectively the different quantum mechanical ground states., Ministerio de Economía y Competitividad (MINECO), French Agence Nationale de la Recherche (ANR) under Contract SurMott, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2004 The American Physical Society., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©American Physical Society. This work was supported by the programs Ramón y Cajal (Ministerio de Ciencia y Tecnología de España) and NanoNed (Dutch Ministry of Economic Affairs)., We argue that the time-resolved spectrum of selectively-excited resonance fluorescence at low temperature provides a tool for probing the quantum-mechanical level repulsion in the Lifshits tail of the electronic density of states in a wide variety of disordered materials. The technique, based on detecting the fast growth of a fluorescence peak that is redshifted relative to the excitation frequency, is demonstrated explicitly by simulations on linear Frenkel exciton chains., program Ramón y Cajal (Ministerio de Ciencia y Tecnología de España), NanoNed (Dutch Ministry of Economic Affairs), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© American Physical Society. The author is grateful to F. Domínguez-Adame, E. Maciá, R. Gutierrez, and V. Malyshev for fruitful discussions, V. M.’s constant encouragement throughout the study and comments on the manuscript are appreciated. This study was supported by MEC under projects Ramón y Cajal and MOSAICO., The combination of self-assembly and electronic properties as well as its true nanoscale dimensions make DNA a promising candidate for a building block of single molecule electronics. We argue that the intrinsic double helix conformation of the DNA strands provides a possibility to drive the electric current through the DNA by the perpendicular electric (gating) field. The transistor effect in the poly(G)-poly(C) synthetic DNA is demonstrated within a simple model approach. We put forward experimental setups to observe the predicted effect and discuss possible device applications of DNA. In particular, we propose a design of the single molecule analog of the Esaki diode., MEC under projects Ramón y Cajal, MOSAICO, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society. A. H. is indebted to Dr. J. M. Rojo and Dr. F. Briones for critical and helpful discussions., The origin of orbital magnetism recently observed in different nanostructured films and particles is discussed as a consequence of spin-orbit coupling. It is shown that contact potentials induced at the thin film surface by broken symmetries, as domain boundaries in self-assembled monolayers, lead to orbital states that in some cases are of large radius. The component of the angular momentum normal to the surface can reach very high values that decrease the total energy by decreasing spin-orbit interaction energy. Intraorbital ferromagnetic spin correlations induce orbital momenta alignment. The estimated values of the magnetic moments per atom are in good agreement with the experimental observations in thiol capped gold films and nanoparticles., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society. Support by Spanish MEyC Projects Nos. NAN2004-09125-C07 and MAT2005-06119 is acknowledged., In this Letter, we report on a crucial experiment showing that magnetic impurities reduce the ferromagnetic order temperature in thiol-capped Au glyconanoparticles (GNPs). The spontaneous magnetization of AuFe GNPs exhibits a fast decrease with temperature that contrasts with the almost constant value of the magnetization observed in Au NPs. Moreover, hysteresis disappears below 300 K. Both features indicate that Fe impurities reduce the high local anisotropy field responsible for the ferromagnetic behavior in Au GNPs. As a consequence, the amazing ferromagnetism in Au NPs should not be associated with the presence of magnetic impurities., Spanish MEC, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© American Physical Society, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2005 The American Physical Society. This work has been partially supported by the University Complutense Project No. PR1/05-13325. Partial support from the EU Network of Excellence SANDIE is also acknowledged., In this Letter, we experimentally show that the room temperature ferromagnetism in the Mn-Zn-O system recently observed is associated with the coexistence of Mn^(3+) and Mn^(4+) via a double-exchange mechanism. The presence of the ZnO around MnO_2 modifies the kinetics of MnO_2 →Mn_2O_3 reduction and favors the coexistence of both Mn oxidation states. The ferromagnetic phase is associated with the interface formed at the Zn diffusion front into Mn oxide, corroborated by preparing thin film multilayers that exhibit saturation magnetization 2 orders of magnitude higher than bulk samples., University Complutense de Madrid, EU Network of Excellence SANDIE, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2004 American Physical Society. XAS facilities at BM29 in ESRF and the technical support from O. Mathon are acknowledged. The authors thank J. Llopis and I. Rosa for helping with optical measurements and sample preparation, respectively. Financial support from the Spanish MCyT under Projects No. MAT2002-04246-C05-05 and No. BQU2002-03734 is acknowledged., We report on the experimental observation of magnetic hysteresis up to room temperature in thiol-capped Au nanoparticles with 1.4 nm size. The coercive field ranges from 860 Oe at 5 K to 250 Oe at 300 K. It is estimated that the Au atoms exhibit a magnetic moment of mu=0.036mu(B). However, Au nanoparticles with similar size but stabilized by means of a surfactant, i.e., weak interaction between protective molecules and Au surface atoms, are diamagnetic, as bulk Au samples are. The apparent ferromagnetism is consequently associated with 5d localized holes generated through Au-S bonds. These holes give rise to localized magnetic moments that are frozen in due to the combination of the high spin-orbit coupling (1.5 eV) of gold and the symmetry reduction associated with two types of bonding: Au-Au and Au-S., Spanish MCyT, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2003 The American Physical Society., We address the relation between long-range correlations and charge transfer efficiency in aperiodic artificial or genomic DNA sequences. Coherent charge transfer through the highest occupied molecular orbital states of the guanine nucleotide is studied using the transmission approach, and the focus is on how the sequence-dependent backscattering profile can be inferred from correlations between base pairs., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2003 The American Physical Society., The onset of ferromagnetism has been experimentally observed in small Pd particles of average diameter 2.4 nm. High-resolution studies reveal that a high percentage of the fcc particle exhibits single and multiple twinning boundaries. The spontaneous magnetization close to 0.02 emu/g seems to indicate that only a small fraction of atoms holds a permanent magnetic moment and contributes to ferromagnetism. The possible origin of ferromagnetism is briefly discussed according to different models recently reported., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2002 The American Physical Society. This work was supported by CONICET, ANPCyT, F. Antorchas (Argentina), and DFG (Germany). M. R. is indebted to J.-P. Dallas (CECM, Vitry) for the single crystals orientation and to A. Traverse (LURE) for valuable support on this project. We thank R. Vianden (ISKP) and A. F. Pasquevich (UNLP) for critical comments., We present an ab initio study of the relaxations introduced in TiO₂ when a Cd impurity substitutes a Ti atom and an experimental test of this calculation by a perturbed-angular-correlation (PAC) measurement of the orientation of the electric-field gradient (EFG) tensor at the Cd site. The ab initio calculation predicts strong anisotropic relaxations of the nearest oxygen neighbors of the impurity and a change of the orientation of the largest EFG tensor component, V_(33) , from the [001] to the [110] direction upon substitution of a Ti atom by a Cd impurity. The last prediction is confirmed by the PAC experiment that shows that V_(33) at the Cd site is parallel to either the [110] or the [1͞10] crystal axis., CONICET, Argentina, ANPCyT, Argentina, Fu. Antorchas, Argentina, DFG, Alemania, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 1997 The American Physical Society., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 1995 The American Physical Society. We thank J. Jefferson, A. Bratkovsky, D. Edwards, D. Sivia, and P. Kornilovitch for stimulating discussions. This work was supported by SERC Grant NO. GR/JI8675 and our general development of SVD techniques by the U.S. Army Research ONce, Agreement No. DAAL03-92- G-0142., The singular value decomposition technique is used to reconstruct the electronic spectral weight function for a half-filled Hubbard model with on-site repulsion U = 4t from quantum Monte Carlo data. A two-band structure for the single-particle excitation spectrum is found to persist as the lattice size exceeds the spin-spin correlation length. The observed bands are flat in the vicinity of the (0, pi), (pi, 0) points in the Brillouin zone, in accordance with experimental data for high-temperature superconducting compounds., SERC, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 1993 The American Physical Society. We acknowledge discussions with A. R. Yavari., In conclusion we have proven that the fact that both fcc FeCu and bcc Fe magnetization agree at 300 K is simply an accident and our data at low temperature show clearly that the Fe contribution after precipitation from the metastable phase has a deficiency in magnetization of at least 20% with respect to the Fe state in fcc FeCu metastable solid solution., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

The authors acknowledge received funding from the project Quantox of QuantERA ERA-NET Cofund in Quantum Technologies (Grant Agreement No. 731473) implemented within the European Union's Horizon 2020 Programme. Work supported by Spanish MINECO through Grants No. MAT2014-52405-C02, No. MAT2017-87134-C02, No. MAT2015-066888-C3-1-3-R, and No. RTI2018-097895-B-C41 (-C43), Grant No. Santander-UCM PR87/19-22603, and computational support from Grant No. FI-2019-1-0012. J. S. thanks for the scholarship program Alembert funded by the IDEX Paris-Saclay, Grant No. ANR-11-IDEX-0003-02., 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., Unión Europea, Ministerio de Economía, Comercio y Empresa (España), Ministerio de Ciencia, Innovación y Universidades (España), Universidad Complutense de Madrid/Banco de Santander, Universidad París-Saclay/ IDEX, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

We study slow-light performance of molecular aggregates arranged in nanofilms by means of coherent population oscillations. The molecular cooperative behavior inside the aggregate enhances the delay of input signals in the gigahertz range in comparison with other coherent population oscillation-based devices. Moreover, the problem of residual absorption present in coherent population oscillation processes is removed. We also propose an optical switch between different delays by exploiting the optical bistability of these aggregates., Ministerio de Educación, Formación Profesional y Deportes (España), Depto. de Física de Materiales, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub