arXiv subjects

Francisco Dominguez-Adame

Publications and source records attributed to Francisco Dominguez-Adame.

At least 19 recordsLinked to original sources

arXiv2026

Topological bound states in the continuum

Bound states in the continuum, originally proposed within the framework of quantum mechanics, have since been observed in a variety of physical contexts, including electromagnetism, acoustics, and optics. Of particular interest are those bound states in the continuum that are protected by continuous symmetries, as their stability makes them resistant to structural imperfections and material disorder. In this study, we demonstrate the existence of topologically protected bound states in the continuum by coupling a finite Su-Schrieffer-Heeger (SSH) chain to a metallic lead. These states are characterized by distinct features in the electrical response of the system, serving as a direct indication of their topological origin. The inherent robustness of such topologically protected states highlights their potential applications in fault-tolerant quantum information processing as well as in the design of advanced electronic and photonic devices.

cond-mat.mes-hall↗

arXiv2023

Polarization-tuneable excitonic spectral features in the optoelectronic response of atomically thin ReS2

The low crystal symmetry of rhenium disulphide (ReS2) leads to the emergence of dichroic optical and optoelectronic response, absent in other layered transition metal dichalcogenides, which could be exploited for device applications requiring polarization resolution. To date, spectroscopy studies on the optical response of ReS2 have relied almost exclusively in characterization techniques involving optical detection, such as photoluminescence, absorbance, or reflectance spectroscopy. However, to realize the full potential of this material, it is necessary to develop knowledge on its optoelectronic response with spectral resolution. In this work, we study the polarization-dependent photocurrent spectra of few-layer ReS2 photodetectors, both in room conditions and at cryogenic temperature. Our spectral measurements reveal two main exciton lines at energies matching those reported for optical spectroscopy measurements, as well as their excited states. Moreover, we also observe an additional exciton-like spectral feature with a photoresponse intensity comparable to the two main exciton lines. We attribute this feature, not observed in earlier photoluminescence measurements, to a non-radiative exciton transition. The intensities of the three main exciton features, as well as their excited states, modulate with linear polarization of light, each one acquiring maximal strength at a different polarization angle. We have performed first-principles exciton calculations employing the Bethe-Salpeter formalism, which corroborate our experimental findings. Our results bring new perspectives for the development of ReS2-based nanodevices.

cond-mat.mtrl-sci↗

arXiv2019

Spin-polarized electron transmission in DNA-like systems

The helical distribution of the electronic density in chiral molecules, such as DNA and bacteriorhodopsin, has been suggested to induce a spin-orbit coupling interaction that may lead to the so-called chirality-induced spin selectivity (CISS) effect. Key ingredients for the theoretical modelling are, in this context, the helically shaped potential of the molecule and, concomitantly, a Rashba-like spin-orbit coupling due to the appearance of a magnetic field in the electron reference frame. Symmetries of these models clearly play a crucial role in explaining the observed effect, but a thorough analysis has been largely ignored in the literature. In this work, we present a study of these symmetries and how they can be exploited to enhance chiral-induced spin selectivity in helical molecular systems.

cond-mat.mes-hall↗

arXiv2000

Multiparticle Biased DLA with surface diffusion: a comprehensive model of electrodeposition

We present a complete study of the Multiparticle Biased Diffusion-Limited Aggregation (MBDLA) model supplemented with surface difussion (SD), focusing on the relevance and effects of the latter transport mechanism. By comparing different algorithms, we show that MBDLA+SD is a very good qualitative model for electrodeposition in practically all the range of current intensities {\em provided} one introduces SD in the model in the proper fashion: We have found that the correct procedure involves simultaneous bulk diffusion and SD, introducing a time scale arising from the ratio of the rates of both processes. We discuss in detail the different morphologies obtained and compare them to the available experimental data with very satisfactory results. We also characterize the aggregates thus obtained by means of the dynamic scaling exponents of the interface height, allowing us to distinguish several regimes in the mentioned interface growth. Our asymptotic scaling exponents are again in good agreement with recent experiments. We conclude by discussing a global picture of the influence and consequences of SD in electrodeposition.

cond-mat.stat-mech↗

arXiv1999

Model for crystallization kinetics: Deviations from Kolmogorov-Johnson-Mehl-Avrami kinetics

We propose a simple and versatile model to understand the deviations from the well-known Kolmogorov-Johnson-Mehl-Avrami kinetics theory found in metal recrystallization and amorphous semiconductor crystallization. We analyze the kinetics of the transformation and the grain size distribution of the product material, finding a good overall agreement between our model and available experimental data. The information so obtained could help to relate the mentioned experimental deviations due to preexisting anisotropy along some regions, to certain degree of crystallinity of the amorphous phases during deposition, or more generally to impurities or roughness of the substrate.

cond-mat.mtrl-sci↗

arXiv1998

Finite temperature dynamics of vortices in the two dimensional anisotropic Heisenberg model

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.

cond-mat.stat-mech↗

arXiv1998

Coherent carrier dynamics in semiconductor superlattices

We investigate the coherent dynamics of carriers in semiconductor superlattices driven by ac-dc electric fields. We solve numerically the time-dependent effective-mass equation for the envelope function. We find that carriers undergo Rabi oscillations when the driving frequency is close to the separation between minibands.

cond-mat.mes-hall↗

arXiv1996

Electric field effects in Fibonacci superlaticces

We present a throughout study of transmission and localization properties of Fibonacci superlattices, both in flat band conditions and subject to homogeneous electric fields perpendicular to the layers. We use the transfer matrix formalism to determine the transmission coefficient and the degree of localization of the electronic states. We find that the fragmentation pattern of the electronic spectrum is strongly modified when the electric field is switched on, this effect being more noticeable as the system length increases. We relate those phenomena to field-induced localization of carriers in Fibonacci superlattices.

cond-mat.mes-hall↗

arXiv1996

Suppresion of Bloch oscillations by weak disorder in semiconductor superlattices

We investigate the dephasing dynamics of Bloch oscillations in semiconductor superlattices by means of a very simple model including disorder and applied electric fields. A thorough numerical study of our model allows us to claim that small, unintentional well width fluctuations can be responsible for fast dephasing of Bloch oscillations at low temperatures. We show that the lifetime of Bloch oscillations is controlled by a characteristic time which depends on the degree of disorder and is independent of the electric field. This result is further supported by the excellent agreement between our model calculations and several recent experiments, and leads to specific new predictions.

cond-mat.mes-hall↗

arXiv1996

Dynamical phenomena in Fibonacci Semiconductor Superlattices

We present a detailed study of the dynamics of electronic wavepackets in Fibonacci semiconductor superlattices, both in flat band conditions and subject to homogeneous electric fields perpendicular to the layers. Coherent propagation of electrons is described by means of a scalar Hamiltonian using the effective-mass approximation. We have found that an initial Gaussian wavepacket is filtered selectively when passing through the superlattice. This means that only those components of the wavepacket whose wavenumber belong to allowed subminibands of the fractal-like energy spectrum can propagate over the entire superlattice. The Fourier pattern of the transmitted part of the wavepacket presents clear evidences of fractality reproducing those of the underlying energy spectrum. This phenomenon persists even in the presence of unintentional disorder due to growth imperfections. Finally, we have demonstrated that periodic coherent-field induced oscillations (Bloch oscillations), which we are able to observe in our simulations of periodic superlattices, are replaced in Fibonacci superlattices by more complex oscillations displaying quasiperiodic signatures, thus sheding more light onto the very peculiar nature of the electronic states in these systems.

cond-mat.mes-hall↗

arXiv1996

Electron dynamics in intentionally disordered semiconductor superlattices

We study the dynamical behavior of disordered quantum-well-based semiconductor superlattices where the disorder is intentional and short-range correlated. We show that, whereas the transmission time of a particle grows exponentially with the number of wells in an usual disordered superlattice for any value of the incident particle energy, for specific values of the incident energy this time increases linearly when correlated disorder is included. As expected, those values of the energy coincide with a narrow subband of extended states predicted by the static calculations of Dom\'ınguez-Adame {\em et al.} [Phys. Rev. B {\bf 51}, 14 ,359 (1994)]; such states are seen in our dynamical results to exhibit a ballistic regime, very close to the WKB approximation of a perfect superlattice. Fourier transform of the output signal for an incident Gaussian wave packet reveals a dramatic filtering of the original signal, which makes us confident that devices based on this property may be designed and used for nanotechnological applications. This is more so in view of the possibility of controllingthe outp ut band using a dc electric field, which we also discuss. In the conclusion we summarize our results and present an outlook for future developments arising from this work.

cond-mat.mes-hall↗

arXiv1996

Long-range effects on optical absorption in quasiperiodic lattices

We consider exciton optical absorption in quasiperiodic lattices, focusing our attention on the Fibonacci case as typical example. The absorption spectrum is evaluated by solving numerically the equation of motion of the Frenkel-exciton problem on the lattice, in which on-site energies take on two values according to the Fibonacci sequence. We find that the quasiperiodic order causes the occurrence of well-defined characteristic features in the absorption spectra. We also develop an analytical method that relates satellite lines with the Fourier pattern of the lattice. Our predictions can be used to determine experimentally the long-range quasiperiodic order from optical measurements.

cond-mat↗

arXiv1996

Can fractal-like spectra be experimentally observed in aperiodic superlattices?

We numerically investigate the effects of inhomogeneities in the energy spectrum of aperiodic semiconductor superlattices, focusing our attention on Thue-Morse and Fibonacci sequences. In the absence of disorder, the corresponding electronic spectra are self-similar. The presence of certain degree of randomness, due to imperfections occurring during the growth processes, gives rise to a progressive loss of quantum coherence, smearing out the finer details of the energy spectra predicted for perfect aperiodic superlattices and spurring the onset of electron localization. However, depending on the degree of disorder introduced, a critical size for the system exists, below which peculiar transport properties, related to the pre-fractal nature of the energy spectrum, may be measured.

cond-mat↗

arXiv1996

Fluorescence decay in aperiodic Frenkel lattices

We study motion and capture of excitons in self-similar linear systems in which interstitial traps are arranged according to an aperiodic sequence, focusing our attention on Fibonacci and Thue-Morse systems as canonical examples. The decay of the fluorescence intensity following a broadband pulse excitation is evaluated by solving the microscopic equations of motion of the Frenkel exciton problem. We find that the average decay is exponential and depends only on the concentration of traps and the trapping rate. In addition, we observe small-amplitude oscillations coming from the coupling between the low-lying mode and a few high-lying modes through the topology of the lattice. These oscillations are characteristic of each particular arrangement of traps and they are directly related to the Fourier transform of the underlying lattice. Our predictions can be then used to determine experimentally the ordering of traps.

cond-mat↗

arXiv1996

Effective Nonlinear Model of Resonant Tunneling Nanostructures

We introduce a model of a nonlinear double-barrier structure, to describe in a simple way the effects of electron-electron scattering while remaining analytically tractable. The model is based on a generalized effective-mass equation where a nonlinear local field interaction is introduced to account for those inelastic scattering phenomena. Resonance peaks seen in the transmission coefficient spectra for the linear case appear shifted to higher energies depending on the magnitude of the nonlinear coupling. Our results are in good agreement with self-consistent solutions of the Schrödinger and Poisson equations. The calculation procedure is seen to be very fast, which makes our technique a good candidate for rapid approximate analysis of these structures.

cond-mat↗

arXiv1995

Physical nature of critical wave functions in Fibonacci systems

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 these critical wave functions and the quasiperiodic order of the underlying lattice.

cond-mat↗

arXiv1995

ELECTRONIC STATES IN GRADED-GAP JUNCTIONS WITH BAND INVERSION

We theoretically study electronic states in graded-gap junctions of IV-VI compounds with band inversion. Using a two-band model within the ${\bf k}\cdot{\bf p}$ approximation and assuming that the gap and the gap centre present linear profiles, we demonstrate the existence of a set of localized states along the growth direction with a discrete energy spectrum. The envelope functions are found to be combination of harmonic oscillator eigenfunctions, and the corresponding energy levels are proportional to the square root of the quantum number. The level spacing can be directly controlled by varying the structure thickness.

cond-mat↗

arXiv1994

Nonlinear treatment of many-body effects in double-barrier resonant tunneling structures

We introduce a simple, solvable model of double-barrier resonant tunneling structure which includes the effects of electron-electron and electron-phonon scattering. The model is based on a generalized effective-mass equation where a nonlinear coupling is introduced to account for those inelastic scattering phenomena. The nonlinear term depends on one parameter which is the only constant in the model to be determined phenomenologically from experimental data. As an example of the application of the model, we discuss GaAs-Ga$_{1-x}$Al$_x$As double-barrier structures. When the nonlinear term is considered, a sideband is observed at an energy of the order of the LO phonon energy in GaAs in addition to and below the main transmission peak. Fitting of the computed spectrum to known experimental results allows to find the value of the nonlinear coupling. As a consequence, we can estimate the electron-phonon coupling from the shift of the main transmission peak in comparison to the linear resonant tunneling. We obtain good agreement with values coming from more sophisticated treatments, which supports our claim that the nonlinear term consistently includes electron-phonon effects. Finally, we use our simple model to study magnitudes of interest for applications, namely $I-V$ characteristics, which are shown to present two negative differential resistance peaks arising from the main transmission peak and the sideband.

cond-mat↗