Centro Mixto CSIC UPV EHU

Donostia / San Sebastián, Spain

Centro Mixto CSIC UPV EHU

Donostia / San Sebastián, Spain
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Petuya R.,Donostia International Physics Center | Arnau A.,Donostia International Physics Center | Arnau A.,Centro Mixto CSIC UPV EHU
Carbon | Year: 2017

The role of a metallic substrate in the interaction between 3d transition metal magnetic atoms adsorbed on graphene is explored for Ir(111), Cu(111) and Ni(111) surfaces. As a general rule, we find that exchange coupling between impurities is essentially determined by the graphene layer and it varies smoothly along the series of 3d atoms for Ir(111) and Cu(111) surfaces, except when resonances appear close to the Fermi level. This universal behavior is at the heart of our main conclusion: the weak interaction between graphene and the underlaying Ir and Cu metal surfaces does not alter appreciably the coupling between magnetic impurities. Therefore, we dare to speculate that previous results based on calculations with freestanding graphene are physically sound and correct. However, in the case of Ni(111) additional effects appear due to the metal surface magnetization. © 2017 Elsevier Ltd

Kuroda K.,Hiroshima University | Miyahara H.,Hiroshima University | Ye M.,Hiroshima University | Eremeev S.V.,Tomsk State University | And 19 more authors.
Physical Review Letters | Year: 2012

The experimental evidence is presented of the topological insulator state in PbBi 2Te 4. A single surface Dirac cone is observed by angle-resolved photoemission spectroscopy with synchrotron radiation. Topological invariants Z 2 are calculated from the ab initio band structure to be 1;(111). The observed two-dimensional isoenergy contours in the bulk energy gap are found to be the largest among the known three-dimensional topological insulators. This opens a pathway to achieving a sufficiently large spin current density in future spintronic devices. © 2012 American Physical Society.

Albanesi D.,French National Center for Scientific Research | Albanesi D.,National University of Rosario | Reh G.,National University of Rosario | Guerin M.E.,Centro Mixto CSIC UPV EHU | And 9 more authors.
PLoS Pathogens | Year: 2013

The biosynthesis of membrane lipids is an essential pathway for virtually all bacteria. Despite its potential importance for the development of novel antibiotics, little is known about the underlying signaling mechanisms that allow bacteria to control their membrane lipid composition within narrow limits. Recent studies disclosed an elaborate feed-forward system that senses the levels of malonyl-CoA and modulates the transcription of genes that mediate fatty acid and phospholipid synthesis in many Gram-positive bacteria including several human pathogens. A key component of this network is FapR, a transcriptional regulator that binds malonyl-CoA, but whose mode of action remains enigmatic. We report here the crystal structures of FapR from Staphylococcus aureus (SaFapR) in three relevant states of its regulation cycle. The repressor-DNA complex reveals that the operator binds two SaFapR homodimers with different affinities, involving sequence-specific contacts from the helix-turn-helix motifs to the major and minor grooves of DNA. In contrast with the elongated conformation observed for the DNA-bound FapR homodimer, binding of malonyl-CoA stabilizes a different, more compact, quaternary arrangement of the repressor, in which the two DNA-binding domains are attached to either side of the central thioesterase-like domain, resulting in a non-productive overall conformation that precludes DNA binding. The structural transition between the DNA-bound and malonyl-CoA-bound states of SaFapR involves substantial changes and large (>30 Å) inter-domain movements; however, both conformational states can be populated by the ligand-free repressor species, as confirmed by the structure of SaFapR in two distinct crystal forms. Disruption of the ability of SaFapR to monitor malonyl-CoA compromises cell growth, revealing the essentiality of membrane lipid homeostasis for S. aureus survival and uncovering novel opportunities for the development of antibiotics against this major human pathogen. © 2013 Albanesi et al.

Bergeret F.S.,Centro Mixto CSIC UPV EHU | Bergeret F.S.,Donostia International Physics Center | Bergeret F.S.,Carl von Ossietzky University | Tokatly I.V.,University of the Basque Country | Tokatly I.V.,Ikerbasque
Physical Review Letters | Year: 2013

The long-range proximity effect in superconductor-ferromagnet (S/F) hybrid nanostructures is observed if singlet Cooper pairs from the superconductor are converted into triplet pairs which can diffuse into the ferromagnet over large distances. It is commonly believed that this happens only in the presence of magnetic inhomogeneities. We show that there are other sources of the long-range triplet component (LRTC) of the condensate and establish general conditions for their occurrence. As a prototypical example, we consider first a system where the exchange field and spin-orbit coupling can be treated as time and space components of an effective SU(2) potential. We derive a SU(2) covariant diffusive equation for the condensate and demonstrate that an effective SU(2) electric field is responsible for the long-range proximity effect. Finally, we extend our analysis to a generic ferromagnet and establish a universal condition for the LRTC. Our results open a new avenue in the search for such correlations in S/F structures and make a hitherto unknown connection between the LRTC and Yang-Mills electrostatics. © 2013 American Physical Society.

Okuda T.,Hiroshima University | Maegawa T.,Hiroshima University | Ye M.,Hiroshima University | Shirai K.,Hiroshima University | And 16 more authors.
Physical Review Letters | Year: 2013

A topological surface state that is protected physically under the Bi 2Te3-like five-layer block has been revealed on the Pb-based topological insulator (TI) PbBi4Te7 by bulk sensitive angle-resolved photoelectron spectroscopy (ARPES). Furthermore, conservation of the spin polarization of the hidden topological surface states is directly confirmed by bulk-sensitive spin ARPES observation. This finding paves the way to realize the real spintronics devices by TIs that are operable in the real environment. © 2013 American Physical Society.

Hofer U.,University of Marburg | Hofer U.,Donostia International Physics Center | Echenique P.M.,Donostia International Physics Center | Echenique P.M.,Centro Mixto CSIC UPV EHU
Surface Science | Year: 2015

A theory of image-potential states is presented for the general case where these surface electronic states are resonant with a bulk continuum. The theory extends the multiple scattering approach of Echenique and Pendry into the strong coupling regime while retaining independence from specific forms of surface and bulk potentials. The theory predicts the existence of a well-resolved series of resonances for arbitrary coupling strengths. Surprisingly, distinct image-potential resonances are thus expected to exist on almost any metal surface, even in the limiting case of jellium. © 2015 Elsevier B.V.

Caprara S.,Donostia International Physics Center | Caprara S.,University of Rome La Sapienza | Tugushev V.V.,RAS Research Center Kurchatov Institute | Chulkov E.V.,Donostia International Physics Center | Chulkov E.V.,Centro Mixto CSIC UPV EHU
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We discuss a model which is apt to describe the appearance of a spin-polarized half-metallic state around a single δ layer of a magnetic transition metal embedded into a nonmagnetic semiconductor host. We show that ferromagnetism in this system can be attributed to the intrinsic physical properties of the δ layer. The relevant physical effects described by our model are the hybridization of the electron states of the metal and semiconductor atoms, the charge redistribution around the δ layer, and the electron-electron correlation on a metal atom, which is the driving force of ferromagnetism. We obtain the mean-field phase diagram of the model at zero and finite temperature, both in the case when the chemical potential is fixed, and when the density of particles on the δ layer is fixed. The relevance of our results in connection with numerical and experimental results on the so-called digital magnetic heterostructures, in the absence and in the presence of a quantum-well carrier channel, is eventually discussed. © 2011 American Physical Society.

Kazansky A.K.,Donostia International Physics Center | Echenique P.M.,Donostia International Physics Center | Echenique P.M.,Centro Mixto CSIC UPV EHU
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The energy loss by an electron ejected from a deep level of an atom adsorbed on Ag(110) surface is considered. It is shown that the dynamical effects in screening of the external field by a metal have to be taken into account and the energy loss by the ejected electron depends on the surface-plasmon dispersion and on the excitation energy. This effect can be observed with contemporary light sources. © 2010 The American Physical Society.

Zhukov V.P.,Donostia International Physics Center | Tyuterev V.G.,Tomsk State Pedagogical University | Chulkov E.V.,Donostia International Physics Center | Chulkov E.V.,Centro Mixto CSIC UPV EHU
Journal of Physics Condensed Matter | Year: 2012

We propose a first-principles method for evaluations of the time-dependent electron distribution function of excited electrons in the conduction band of semiconductors. The method takes into account the excitations of electrons by an external source and the relaxation to the bottom of the conduction band via electron-phonon coupling. The methods permit calculations of the non-equilibrium electron distribution function, the quasi-stationary distribution function with a steady-in-time source of light, the time of setting of the quasi-stationary distribution and the time of energy loss via relaxation to the bottom of the conduction band. The actual calculations have been performed for titanium dioxide in the anatase structure and zinc oxide in the wurtzite structure. We find that the quasi-stationary electron distribution function has a peak near the bottom of the conduction band and a tail whose maximum energy rises linearly with increasing energy of excitation. The calculations demonstrate that the relaxation of excited electrons and the setting of the quasi-stationary distribution occur within a time of no more than 500fs for ZnO and 100fs for anatase. We also discuss the applicability of the effective phonon model to energy-independent electron-phonon transition probability. We find that the model only reproduces the trends in the change of the characteristic times whereas the precision of such calculations is not high. The rate of energy transfer to phonons at the quasi-stationary electron distribution also have been evaluated and the effect of this transfer on the photocatalysis has been discussed. We found that for ZnO this rate is about five times less than in anatase. © 2012 IOP Publishing Ltd.

Borisova S.D.,Tomsk State University | Rusina G.G.,Tomsk State University | Eremeev S.V.,Tomsk State University | Chulkov E.V.,Centro Mixto CSIC UPV EHU
JETP Letters | Year: 2016

Equilibrium lengths and binding energies, vibrational frequencies, width of the HOMO–LUMO gap, and the magnetic anisotropy energies for one- and two-component dimers of heavy p elements of Groups IV (Sn, Pb), V (Sb, Bi), and VI (Se, Te) with a pronounced relativistic effect have been calculated with the use of the formalism of the density functional theory. It has been shown that it is necessary to take into account the spin–orbit coupling, which significantly affects the energy parameters of clusters. The analysis of the data obtained has revealed that the Pb–Te, Pb–Se, Sn–Te, and Sn–Se dimers have the widest gap at the Fermi level and the lowest reactivity. The magnetic anisotropy energy has been calculated for all single- and doublecomponent dimers and the direction of the easy magnetization axis has been determined. © 2016, Pleiades Publishing, Inc.

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