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Search Results: 1 - 10 of 550175 matches for " J. Sánchez-Barriga "
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Massless Dirac fermions in epitaxial graphene on Fe(110)
A. Varykhalov,J. Sánchez-Barriga,P. Hlawenka,O. Rader
Physics , 2012,
Abstract: Graphene grown on Fe(110)by chemical vapor deposition using propylene is investigated by means of angle-resolved photoemission. The presence of massless Dirac fermions is clearly evidenced by the observation of a fully intact Dirac cone. Unlike Ni(111) and Co(0001), the Fe(110) imposes a strongly anisotropic quasi-one-dimensional structure on the graphene. Certain signatures of a superlattice effect appear in the dispersion of its \sigma-bands but the Dirac cone does not reveal any detectable superlattice or quantum-size effects although the graphene corrugation is twice as large as in the established two-dimensional graphene superlattice on Ir(111).
Rashba splitting of 100 meV in Au-intercalated graphene on SiC
D. Marchenko,A. Varykhalov,J. Sánchez-Barriga,Th. Seyller,O. Rader
Physics , 2015,
Abstract: Intercalation of Au can produce giant Rashba-type spin-orbit splittings in graphene but this has not yet been achieved on a semiconductor substrate. For graphene/SiC(0001), Au intercalation yields two phases with different doping. Here, we report the preparation of an almost pure p-type graphene phase after Au intercalation. We observe a 100 meV Rashba-type spin-orbit splitting at 0.9 eV binding energy. We show that this giant splitting is due to hybridization and much more limited in energy and momentum space than for Au-intercalated graphene on Ni.
Ferrimagnetic nanostructures for magnetic memory bits
A. A. ünal,S. Valencia,D. Marchenko,K. J. Merazzo,F. Radu,M. Vázquez,J. Sánchez-Barriga
Physics , 2015,
Abstract: Increasing the magnetic data recording density requires reducing the size of the individual memory elements of a recording layer as well as employing magnetic materials with temperature-dependent functionalities. Therefore, it is predicted that the near future of magnetic data storage technology involves a combination of energy-assisted recording on nanometer-scale magnetic media. We present the potential of heat-assisted magnetic recording on a patterned sample; a ferrimagnetic alloy composed of a rare earth and a transition metal, DyCo$_5$, which is grown on a hexagonal-ordered nanohole array membrane. The magnetization of the antidot array sample is out-of-plane oriented at room temperature and rotates towards in-plane upon heating above its spin-reorientation temperature (T$_R$) of ~350 K, just above room temperature. Upon cooling back to room temperature (below T$_R$), we observe a well-defined and unexpected in-plane magnetic domain configuration modulating with ~45 nm. We discuss the underlying mechanisms giving rise to this behavior by comparing the magnetic properties of the patterned sample with the ones of its extended thin film counterpart. Our results pave the way for novel applications of ferrimagnetic antidot arrays of superior functionality in magnetic nano-devices near room temperature.
High spin polarization and circular dichroism of topological surface states on Bi2Te3
M. R. Scholz,J. Sánchez-Barriga,D. Marchenko,A. Varykhalov,A. Volykhov,L. V. Yashina,O. Rader
Physics , 2011,
Abstract: Topological insulators have been successfully identified by spin-resolved photoemission but the spin polarization remained low (~20%). We show for Bi2Te3 that the in-gap surface state is much closer to full spin polarization with measured values reaching 80% at the Fermi level. When hybridizing with the bulk it remains highly spin polarized which may explain recent unusual quantum interference results on Bi2Se3. The topological surface state shows a large circular dichroism in the photoelectron angle distribution with an asymmetry of ~20% the sign of which corresponds to that of the measured spin.
Tolerance of topological surface states towards magnetic moments: Fe on Bi2Te3 and Bi2Se3
M. R. Scholz,J. Sánchez-Barriga,D. Marchenko,A. Varykhalov,A. Volykhov,L. V. Yashina,O. Rader
Physics , 2011, DOI: 10.1103/PhysRevLett.108.256810
Abstract: Topological insulators(1-8) are a novel form of matter which features metallic surface states with quasirelativistic dispersion similar to graphene(9). Unlike graphene, the locking of spin and momentum and the protection by time-reversal symmetry(1-8) open up tremendous additional possibilities for external control of transport properties(10-18). Here we show by angle-resolved photoelectron spectroscopy that the topological sur-face states of Bi2Te3 and Bi2Se3 are stable against the deposition of Fe without opening a band gap. This stability extends to low submonolayer coverages meaning that the band gap reported recently(19) for Fe on Bi2Se3 is incorrect as well as to complete monolayers meaning that topological surface states can very well exist at interfaces with ferromagnets in future devices.
Ultrafast spin polarization control of Dirac fermions in topological insulators
J. Sánchez-Barriga,E. Golias,A. Varykhalov,J. Braun,L. V. Yashina,R. Schumann,J. Minár,H. Ebert,O. Kornilov,O. Rader
Physics , 2015,
Abstract: Three-dimensional topological insulators (TIs) are characterized by spin-polarized Dirac-cone surface states that are protected from backscattering by time-reversal symmetry. Control of the spin polarization of topological surface states (TSSs) using femtosecond light pulses opens novel perspectives for the generation and manipulation of dissipationless surface spin currents on ultrafast timescales. Using time-, spin-, and angle-resolved spectroscopy, we directly monitor for the first time the ultrafast response of the spin polarization of photoexcited TSSs to circularly-polarized femtosecond pulses of infrared light. We achieve all-optical switching of the transient out-of-plane spin polarization, which relaxes in about 1.2 ps. Our observations establish the feasibility of ultrafast optical control of spin-polarized Dirac fermions in TIs and pave the way for novel optospintronic applications at ultimate speeds.
Angle-resolved and core-level photoemission study of interfacing the topological insulator Bi1.5Sb0.5Te1.7Se1.3 with Ag, Nb and Fe
N. de Jong,E. Frantzeskakis,B. Zwartsenberg,Y. K. Huang,D. Wu,P. Hlawenka,J. Sánchez-Barriga,A. Varykhalov,E. van Heumen,M. S. Golden
Physics , 2015, DOI: 10.1103/PhysRevB.92.075127
Abstract: Interfaces between a bulk-insulating topological insulator (TI) and metallic adatoms have been studied using high-resolution, angle-resolved and core-level photoemission. Fe, Nb and Ag were evaporated onto Bi1.5Sb0.5Te1.7Se1.3 (BSTS) surfaces both at room temperature and 38K. The coverage- and temperature-dependence of the adsorption and interfacial formation process have been investigated, highlighting the effects of the overlayer growth on the occupied electronic structure of the TI. For all coverages at room temperature and for those equivalent to less than 0.1 monolayer at low temperature all three metals lead to a downward shift of the TI's bands with respect to the Fermi level. At room temperature Ag appears to intercalate efficiently into the van der Waals gap of BSTS, accompanied by low-level substitution of the Te/Se atoms of the termination layer of the crystal. This Te/Se substitution with silver increases significantly for low temperature adsorption, and can even dominate the electrostatic environment of the Bi/Sb atoms in the BSTS near-surface region. On the other hand, Fe and Nb evaporants remain close to the termination layer of the crystal. On room temperature deposition, they initially substitute isoelectronically for Bi as a function of coverage, before substituting for Te/Se atoms. For low temperature deposition, Fe and Nb are too immobile for substitution processes and show a behaviour consistent with clustering on the surface. For both Ag and Fe/Nb, these differing adsorption pathways leads to the qualitatively similar and remarkable behavior for low temperature deposition that the chemical potential first moves upward (n-type dopant behavior) and then downward (p-type behavior) on increasing coverage.
Anisotropic effect of warping on the lifetime broadening of topological surface states in angle-resolved photoemission from Bi$_2$Te$_3$
J. Sánchez-Barriga,M. R. Scholz,E. Golias,E. Rienks,D. Marchenko,A. Varykhalov,L. V. Yashina,O. Rader
Physics , 2015, DOI: 10.1103/PhysRevB.90.195413
Abstract: We analyze the strong hexagonal warping of the Dirac cone of Bi$_2$Te$_3$ by angle-resolved photoemission. Along $\overline{\Gamma}$$\overline{\rm M}$, the dispersion deviates from a linear behavior meaning that the Dirac cone is warped outwards and not inwards. We show that this introduces an anisotropy in the lifetime broadening of the topological surface state which is larger along $\overline{\Gamma}$$\overline{\rm K}$. The result is not consistent with nesting. Based on the theoretically predicted behavior of the ground-state spin texture of a strongly warped Dirac cone, we propose spin-dependent scattering processes as explanation for the anisotropic scattering rates. These results could help paving the way for optimizing future spintronic devices using topological insulators and controlling surface-scattering processes via external gate voltages.
Mortality trends from diabetes mellitus in the seven socioeconomic regions of Mexico, 2000-2007
Sánchez-Barriga,Juan Jesús;
Revista Panamericana de Salud Pública , 2010, DOI: 10.1590/S1020-49892010001100007
Abstract: objective: to determine trends in mortality from diabetes mellitus nationwide according to federative entity, socioeconomic region, and sex and to establish the association between education level, federation entity of residence, and socioeconomic region and mortality from diabetes in mexico during the years 2000-2007. methods: records of mortality associated with diabetes for 2000-2007 were obtained from the national information system of the secretariat of health. this information is generated by the national institute of statistics, geography and informatics through death certificates. codes of international classification of diseases, 10th revision, that correspond to the basic cause of death from diabetes mellitus were identified. rates of mortality by federative entity and socioeconomic region were calculated, along with the strength of association (obtained by poisson regression) between federative entity of residence, socioeconomic region, and education level and mortality from diabetes. the seven socioeconomic regions elaborated by the national institute of statistics, geography and informatics include the 32 federative entities according to indicators related to well-being such as education, occupation, health, housing, and employment. results: individuals who did not complete elementary school had a higher risk of dying from diabetes (relative risk [rr] 2.104, 95% confidence interval [ci] 2.089-2.119). the federative entity and socioeconomic region with the strongest association with mortality from diabetes were mexico city (rr 2.5, ci 2.33-2.68 for 2000; rr 2.06, ci 1.95-2.18 for 2007) and region 7 (rr 2.47, ci 2.36-2.57 for 2000; rr 2.05, ci 1.98-2.13 for 2007). conclusions: mortality rates increased from 77.9 to 89.2 per 100 000 inhabitants in the period 2000-2007. women had higher mortality than men. individuals who did not complete elementary school had a higher risk of dying from diabetes (rr 2.104, ci 2.089-2.119). mexico city as federative entity
Photoemission of Bi$_2$Se$_3$ with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?
J. Sánchez-Barriga,A. Varykhalov,J. Braun,S. -Y. Xu,N. Alidoust,O. Kornilov,J. Minár,K. Hummer,G. Springholz,G. Bauer,R. Schumann,L. V. Yashina,H. Ebert,M. Z. Hasan,O. Rader
Physics , 2013, DOI: 10.1103/PhysRevX.4.011046
Abstract: Topological insulators are characterized by Dirac cone surface states with electron spins aligned in the surface plane and perpendicular to their momenta. Recent theoretical and experimental work implied that this specific spin texture should enable control of photoelectron spins by circularly polarized light. However, these reports questioned the so far accepted interpretation of spin-resolved photoelectron spectroscopy. We solve this puzzle and show that vacuum ultraviolet photons (50-70 eV) with linear or circular polarization probe indeed the initial state spin texture of Bi$_2$Se$_3$ while circularly polarized 6 eV low energy photons flip the electron spins out of plane and reverse their spin polarization. Our photoemission calculations, considering the interplay between the varying probing depth, dipole selection rules and spin-dependent scattering effects involving initial and final states explain these findings, and reveal proper conditions for light-induced spin manipulation. This paves the way for future applications of topological insulators in opto-spintronic devices.
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