Person: Domínguez-Adame Acosta, Francisco
Universidad Complutense de Madrid
Faculty / Institute
Física de Materiales
Física de la Materia Condensada
Now showing 1 - 10 of 180
PublicationDelocalized vibrations in classical random chains(American Physical Society, 1993-09-01) Domínguez-Adame Acosta, Francisco; Maciá Barber, Enrique Alfonso; Sánchez, AngelNormal modes of one-dimensional disordered chains with two couplings, one of them assigned at random to pairs in an otherwise perfect chain, are investigated. We diagonalize the dynamical matrix to find the normal modes and to study their spatial extent. Multifractal analysis is used to discern clearly the localized or delocalized character of vibrations. In constrast to the general viewpoint that all normal modes in one dimensional random chains are localized, we find a set of extended modes close to a critical frequency, whose number increases with the system size and becomes independent of the defect concentration. PublicationComposition dependence of cathodoluminescence emission of Al_xGa_(1−x)P(Pergamon-Elsevier Science LTD, 1990-10) Fernández Sánchez, Paloma; Domínguez-Adame Acosta, Francisco; Piqueras de Noriega, Javier; Armelles, G.Cathodoluminescence of AlxGa1−xP has been investigated for x between 0.10 and 0.53. A band corresponding to the 610 nm band of pure GaP has been found to shift to higher energies with increasing x. The position of a red band centred at 690 nm is independent of x. PublicationSuper Bloch oscillations in the Peyrard-Bishop-Holstein model(Elsevier, 2012-01-09) Herrero-Gomez, C.; Díaz García, Elena; Domínguez-Adame Acosta, FranciscoRecently, polarons in the Peyrard-Bishop-Holstein model under DC electric fields were established to perform Bloch oscillations, provided the charge-lattice coupling is not large. In this work, we study this model when the charge is subjected to an applied field with both DC and AC components. Similarly to what happens in the rigid lattice, we find that the carrier undergoes a directed motion or coherent oscillations when the AC field is resonant or detuned with respect to the Bloch frequency, respectively. The electric density current and its Fourier spectrum are also studied to reveal the frequencies involved in the polaron dynamics. PublicationLinear optical properties of one-dimensional Frenkel exciton systems with intersite energy correlations(American Physical Society, 1999-11-15) Malyshev, Andrey; Rodriguez, A.; Domínguez-Adame Acosta, FranciscoWe analyze the effects of intersite energy correlations on the linear optical properties of one-dimensional disordered Frenkel exciton systems. The absorption linewidth and the factor of radiative rate enhancement are studied as a function of the correlation length of the disorder. Thr absorption line width monotonously approaches the seeding degree of disorder on increasing the correlation length. On the contrary, the factor of radiative rate enhancement shows a nonmonotonous trend, indicating a complicated scenario of the exciton localization in correlated systems. The concept of coherently bound molecules is exploited to explain the numerical results, showing good agreement with theory. Some recent experiments are discussed in the light of the present theory. [S0163-1829(99)07343-9]. PublicationBias driven coherent carrier dynamics in a two-dimensional aperiodic potential(Elsevier, 2008-10-27) Moura, F. A. B. F., de; Viana, L. P.; Lyra, M. L.; Malyshev, Andrey; Domínguez-Adame Acosta, FranciscoWe study the dynamics of an electron wave-packet in a two-dimensional square lattice with an aperiodic site potential in the presence of an external uniform electric field. The aperiodicity is described by epsilon(m) = V cos(pi alpha m(x)(nu x)) cos(pi alpha m(y)(nu y)) at lattice sites (m(x),m(y)), with pi alpha being a rational number, and v(x) and v(y) tunable parameters. controlling the aperiodicity. Using an exact diagonalization procedure and a finite-size scaling analysis, we show that in the weakly aperiodic regime (nu(x), nu(y) < 1), a phase of extended states emerges in the center of the band at zero field giving support to a macroscopic conductivity in the thermodynamic limit. Turning on the field gives rise to Bloch oscillations of the electron wave-packet. The spectral density of these oscillations may display a double peak structure signaling the spatial anisotropy of the potential landscape. The frequency of the oscillations can be understood using a semi-classical approach. PublicationComment on "Sequencing-independent delocalization in a DNA-like double chain with base pairing"(American Physical Society, 2006-02-10) Sedrakyan, A.; Domínguez-Adame Acosta, Francisco PublicationTailoring topological states of core-shell nanoparticles(Elsevier Science BV, 2022-02) Martínez Strasser, Carolina; Baba, Yuriko; Díaz Fernández, Álvaro; Domínguez-Adame Acosta, FranciscoIn this work we investigate novel spherical core-shell nanoparticles with band inversion. The core and the embedding medium are normal semiconductors while the shell material is assumed to be a topological insulator. The envelope functions are found to satisfy a Dirac-like equation that can be solved in a closed form. The core-shell nanoparticle supports midgap bound states located at both interfaces due to band inversion. These states are robust since they are topologically protected. The energy spectrum presents mirror symmetry due to the chiral symmetry of the Dirac-like Hamiltonian. As a major result, we show that the thickness of the shell acts as an additional parameter for the fine tuning of the energy levels, which paves the way for electronics and optoelectronics applications. PublicationFinite temperature dynamics of vortices in the two dimensional anisotropic Heisenberg model(Springer, 1998) Kamppeter, Till; Mertens, Franz G.; Sánchez, Angel; Bishop, A. R.; Domínguez-Adame Acosta, Francisco; Grønbech-Jensen, N.We study the effects of finite temperature on the dynamics of non-planar vortices in the classical, two-dimensional anisotropic Heisenberg model with XY- or easy-plane symmetry. To this end, we analyze a generalized Landau-Lifshitz equation including additive white noise and Gilbert damping. Using a collective variable theory with no adjustable parameters we derive an equation of motion for the vortices with stochastic forces which are shown to represent white noise with an effective diffusion constant linearly dependent on temperature. We solve these stochastic equations of motion by means of a Green's function formalism and obtain the mean vortex trajectory and its variance. We find a non-standard time dependence for the variance of the components perpendicular to the driving force. We compare the analytical results with Langevin dynamics simulations and find a good agreement up to temperatures of the order of 25% of the Kosterlitz-Thouless transition temperature. Finally, we discuss the reasons why our approach is not appropriate for higher temperatures as well as the discreteness effects observed in the numerical simulations. PublicationExplanation of delocalization in the continuous random-dimer model(American Physical Society, 1995-03-01) Sánchez, Angel; Domínguez-Adame Acosta, Francisco; Berman, Gennady P.; Izrailev, FelixWe propose an explanation of the bands of extended states appearing in random one-dimensional models with correlated disorder, focusing on the continuous random-dimer model [A. Sanchez, E. Macia, and F. Dominguez-Adame, Phys. Rev. B 49, 147 (1994)].We show exactly that the transmission coefficient at the resonant energy is independent of the number of host sites between two consecutive dimers. This allows us to understand why there are bands of extended states for every realization of the model as well as the dependence of the bandwidths on the concentration. We carry out a perturbative calculation that sheds more light on the above results. In the conclusion we discuss generalizations of our results to other models and possible applications which arise from insight into this problem. PublicationLocalisation and finite-size effects in graphene flakes(EPL Association, European Physical Society, 2013-10) González-Santander de la Cruz, Clara; Domínguez-Adame Acosta, Francisco; Hilke, M.; Roemer, R. A.We show that electron states in disordered graphene, with an onsite potential that induces inter-valley scattering, are localised for all energies at disorder as small as 1/6 of the band width of clean graphene. We clarify that, in order for this Anderson-type localisation to be manifested, graphene flakes of size approximate to 200 x 200 nm(2) or larger are needed. For smaller samples, due to the surprisingly large extent of the electronic wave functions, a regime of apparently extended (or even critical) states is identified. Our results complement earlier studies of macroscopically large samples and can explain the divergence of results for finite-size graphene flakes.