Papers by Catalina Lopez-Bastidas
Using the recently proposed definition of a conserved spin-current operator [J. Shi et al., Phys.... more Using the recently proposed definition of a conserved spin-current operator [J. Shi et al., Phys. Rev. Lett. 96, 076604 (2006)] we explore the frequency dependent spin Hall conductivity for a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interaction in response to an oscillating electric field. We show that the optical spectrum of the spin Hall conductivity exhibit remarkable changes when the new definition of spin current is applied. Such behavior is mainly due to a significant contribution of the spin torque term which is absent in the conventional form of the spin current. In addition, it is observed that the magnitude and direction of the dynamic spin Hall current strongly depends on the electric field frequency as with the interplay of the spin-orbit coupling strengths.
SPIE Proceedings, 2004
Nonlinear optical nanoscope with depth resolution. [Proceedings of SPIE 5622, 524 (2004)]. W. Lui... more Nonlinear optical nanoscope with depth resolution. [Proceedings of SPIE 5622, 524 (2004)]. W. Luis Mochan, Catalina Lopez-Bastidas, Jesus A. Maytorena, Bernardo S. Mendoza, Vera L. Brudny. Abstract. Existing optical scanning ...
At a certain energy interval the collective surface excitations play an important role in the die... more At a certain energy interval the collective surface excitations play an important role in the dielectric response of metal interfaces. These phenomena are frequently invoked as energy dispersing channels to be considered in the calculation of optical properties, excited state relaxation times or other dynamic quantities. The physical mechanisms that affect the dispersion relation include band structure effects on the s-electron response as well as d-electron polarization. The spatial distribution of the d-electron density has been shown to contribute to the crystal face orientation dependence of the surface plasmon dispersion relation. In this work we compare the theoretical excitation spectra of Ag single crystal surfaces obtained by different models. We identify the mechanisms present in each approach and discuss their final effect on the dispersion relation of collective modes within it. A comparison with available experimental data is also presented.
Submitted for the MAR09 Meeting of The American Physical Society Size dependent thermalization ti... more Submitted for the MAR09 Meeting of The American Physical Society Size dependent thermalization time of Ag nanoparticles and the surface density profile CATALINA LOPEZ
Physica B: Condensed Matter, 2003
The bulk macroscopic dielectric response of a disordered composite is calculated employing a larg... more The bulk macroscopic dielectric response of a disordered composite is calculated employing a large finite sample instead of an infinite one obtained by replicating a unit cell, as has usually been done. We explicitly account for boundary effects through the macroscopic depolarization field, and finite size corrections are minimized by the large size of the system. The generation of the composite and the calculation of the interactions between the great number of particles become feasible using a newly developed hierarchical multi-resolution scheme. The dielectric response of a composite made up of Ag spheres embedded in glass and the composition independent spectral density agree with those from previous simulations and we discuss their differences with analytical theories based on a renormalized polarizability. Confinement effects due to inhomogeneities close to the boundary of the system are also investigated. r
The spin Hall effect in spin-orbit coupled systems has lately attracted great attention. Since th... more The spin Hall effect in spin-orbit coupled systems has lately attracted great attention. Since the electron spin is not a conserved quantity in spin-orbit coupled systems, the conventional form for the spin current operator turn out to be ill-defined. A fundamental issue is then a proper definition of spin current in such systems. Recently J. Shi et. al. [1] introduced
Journal of Nanophotonics, 2015
Physical Review B, 2001
The surface plasmon dispersion relation of Ag is calculated for different single-crystal orientat... more The surface plasmon dispersion relation of Ag is calculated for different single-crystal orientations. To describe the dynamical response properties of both delocalized 5s electrons and more tightly bound 4d electrons, the jellium model is combined with the so-called dipolium model, in which the occupied Ag d bands are represented in terms of polarizable spheres located at the sites of a semi-infinite fcc lattice. The nonlocal susceptibility characterizing the s electron response in the surface region is derived using density functional theory. The screening of the Coulomb interaction between conduction electrons via the lattice of dipoles, and of the dipole interaction via the surrounding sea of conduction electrons, is treated self-consistently. Electron energy loss spectra are calculated for all three low-index faces. The surface plasmon energy is found to increase with parallel wave vector for all cases. The magnitude of the positive slope depends on the crystal orientation and, for Ag͑110͒, on the propagation direction. These results are in qualitative agreement with electron energy loss measurements.
We calculate the dielectric response of a two-dimensional electron gas with both Rashba and Dress... more We calculate the dielectric response of a two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit (SO) coupling within the self-consistent-field approach. We obtain the dispersion relations of the collective modes and the regions of single-particle excitations, related with intra- and inter-spin-split transitions. The interplay of both types of SO couplings give rise to an angular anisotropy of the spin-splitting
Applied Surface Science, 2014
ABSTRACT Gold nanoparticles supported on Y-zeolite were prepared using the [Au(NH3)4](NO3)3 compl... more ABSTRACT Gold nanoparticles supported on Y-zeolite were prepared using the [Au(NH3)4](NO3)3 complex as gold precursor. The differences in the formation of gold nanoparticles in the presence of various co-cations (Na, Cu, Ni or Fe) were discussed in this work. The shift in the plasmon peak observed in the UV-vis spectra for different sample compositions was linked with variation in Au nanoparticle size, as well as changes in the sample chemical composition under thermal treatment. Theoretical spectra for Au nanoparticles supported on modified zeolites were obtained applying an average field model. Qualitative comparison of the data with the theoretical spectra yields insight into the role of distinct co-cations in the system.
Physical Review B, 2001
The dynamics of excited electronic states at Ag surfaces is studied by evaluating the quasipartic... more The dynamics of excited electronic states at Ag surfaces is studied by evaluating the quasiparticle selfenergy within the GW approximation. The screened Coulomb interaction W is shown to be sensitive to the spatial variation of s-d screening near the surface. In the region of s-electron spill-out electronic damping is stronger than in the bulk due to the reduced s-d polarization, giving rise to shorter surface-state lifetimes. The lifetime of Ag image states is expected to be strongly reduced due to decay into surface plasmons.
Plasmonics: Metallic Nanostructures and Their Optical Properties XII, 2014
Plasmonics: Metallic Nanostructures and Their Optical Properties XII, 2014
Plasmonics, 2013
ABSTRACT The plasmonic features in the optical response of coinage metal nanoparticles supported ... more ABSTRACT The plasmonic features in the optical response of coinage metal nanoparticles supported on different type of zeolites were studied. The shifts in the plasmon frequency were analyzed for Cu, Ag, and Au nanoparticles in mordenite, β-zeolite, and Y-zeolite. It was shown experimentally that the resonance energy is sensitive both to type of zeolite structure and counter-cation of zeolite, as well as to annealing temperature and chemical composition of zeolite, their SiO2/Al2O3 molar ratio. A theoretical framework was employed to identify physical mechanism for this sensitivity. Within a simple model, the width of the absorption window identified in the imaginary part of the bulk dielectric function of the different metals was seen to play the important role in establishing the range of the plasmon energies available. In terms of an effective dielectric function, the composite medium was fully described by the complex dielectric function of the metal involved, the dissipation-free dielectric function of the zeolite matrix, and the filling fraction which relates the volume of metal inclusions as a fraction of the total sample volume. The sensitivity of the optical spectra is understood in terms of variations in both the dielectric response of the zeolite matrix as well as nanoparticle size.
Physical Review B, 1999
... Sci. 377-379, 388 (1997) [INSPEC]. PHYSICAL REVIEW B VOLUME 60, NUMBER 11 15 SEPTEMBER 1999-I... more ... Sci. 377-379, 388 (1997) [INSPEC]. PHYSICAL REVIEW B VOLUME 60, NUMBER 11 15 SEPTEMBER 1999-I Surface plasmon dispersion at silver single-crystal surfaces ?Catalina Lopez-Bastidas* ? Facultad de Ciencias, Universidad ...
physica status solidi (b), 2003
An electromagnetic field forced to vary along a plane with a spatial scale d much smaller than it... more An electromagnetic field forced to vary along a plane with a spatial scale d much smaller than its free space wavelength λ decays exponentially along its normal with a decay length ¡ d. This decay, similar to that of the wavefunction of tunneling electrons, has allowed the development of scanning near-field optical microscopes (SNOMs), reminiscent of scanning tunneling and atomic force microscopes, which have been able to resolve structures in the nanometer scale. However, existing SNOMs are unable to determine the depth below the surface from which the optical signals arise due to the monotonic decay of the optical evanescent probe fields. In this paper we study the optical second harmonic generation (SHG) produced by mixing of the evanescent fields produced by a SNOM tip. We show that employing an appropriately spatially-patterned tip, a non-monotonic non-linear probing field may be produced which has a maximum at a given distance beyond the tip, yielding a novel microscopy which may attain depth resolution with nanometric lengthscales. We estimate the size of the optical signal and we compare it with that arising in the usual SHG-based surface spectroscopy of centrosymmetric materials.
Physical Review B, 2006
We study the frequency dependent spin-and charge-conductivity tensors of a two-dimensional electr... more We study the frequency dependent spin-and charge-conductivity tensors of a two-dimensional electron gas (2DEG) with Rashba and Dresselhaus spin-orbit interaction. We show that the angular anisotropy of the spin-splitting energy induced by the interplay between the Rashba and Dresselhaus couplings gives rise to a characteristic spectral behavior of the spin and charge response which is significantly different from that of pure Rashba or Dresselhaus case. Such new spectral structures open the possibility for control of the optical response by applying an external bias and/or by adjusting the light frequency. In addition, it is shown that the relative strength of the spin-orbit coupling parameters can be obtained through optical probing.
Physical Review B, 2008
Using the recently proposed definition of a conserved spin-current operator [J. Shi et al., Phys.... more Using the recently proposed definition of a conserved spin-current operator [J. Shi et al., Phys. Rev. Lett. 96, 076604 (2006)] we explore the frequency dependent spin Hall conductivity for a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interaction in response to an oscillating electric field. We show that the optical spectrum of the spin Hall conductivity exhibit remarkable changes when the new definition of spin current is applied. Such behavior is mainly due to a significant contribution of the spin torque term which is absent in the conventional form of the spin current. In addition, it is observed that the magnitude and direction of the dynamic spin Hall current strongly depends on the electric field frequency as with the interplay of the spin-orbit coupling strengths.
physica status solidi (c), 2007
Published online zzz PACS 73.63. Kv, 73.21.La, 72.25.Dc We present calculations of the frequency-... more Published online zzz PACS 73.63. Kv, 73.21.La, 72.25.Dc We present calculations of the frequency-dependent spin susceptibility tensor of a two-dimensional electron gas with competing Rashba and Dresselhaus spin-orbit interaction. It is shown that the interplay between both types of spin-orbit coupling gives rise to an anisotropic spectral behavior of the spin density response function which is significantly different from that of vanishing Rashba or Dresselhaus case. Strong resonances are developed in the spin susceptibility as a consequence of the angular anisotropy of the energy spin-splitting. This characteristic optical modulable response may be useful to experimentally probe spin accumulation and spin density currents in such systems.
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Papers by Catalina Lopez-Bastidas