Person:
Maciá Barber, Enrique Alfonso

First Name

Enrique Alfonso

Last Name

Maciá Barber

URI

https://hdl.handle.net/20.500.14352/75005

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de Materiales

Area

Física de la Materia Condensada

Identifiers

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Search Results

Now showing 1 - 10 of 60

Suppression of localization in kronig-penney models with correlated disorder
(Physical Review B, 1994) Sáchez, A.; Maciá Barber, Enrique Alfonso; Domínguez-Adame Acosta, Francisco
We consider the electron dynamics and transport properties of one-dimensional continuous models with random, short-range correlated impurities. We develop a generalized Poincare map formalism to cast the Schrodinger equation for any potential into a discrete set of equations, illustrating its application by means of a specific example. We then concentrate on the case of a Kronig-Penney model with dimer impurities. The previous technique allows us to show that this model presents infinitely many resonances (zeroes of the reflection coefficient at a single dimer) that give rise to a band of extended states, in contradiction with the general viewpoint that all one-dimensional models with random potentials support only localized states. We report on exact transfer-matrix numerical calculations of the transmission coefFicient, density of states, and localization length for various strengths of disorder. The most important conclusion so obtained is that this kind of system has a very large number of extended states. Multifractal analysis of very long systems clearly demonstrates the extended character of such states in the thermodynamic limit. In closing, we brieBy discuss the relevance of these results in several physical contexts.
Codon thermoelectric signature in molecular junctions
(Physical review B, 2010) Maciá Barber, Enrique Alfonso
The thermoelectric power of trimer oligonucleotides connected in between metallic contacts at different temperatures is theoretically studied. The obtained analytical expressions reveal the existence of important resonance effects leading to a significant thermopower enhancement for certain characteristic energies which depend on the specific electronic structure of considered codons. This result suggests the existence of a thermoelectric signature for different triplet associations of biological interest.
Electronic structure and transport properties of double-stranded Fibonacci DNA
(Physical review B, 2006) Maciá Barber, Enrique Alfonso
We consider a class of synthetic DNA molecules based on a quasiperiodic arrangement of their constituent nucleotides. Making use of a two-step renormalization scheme the double-stranded DNA molecule is modeled in terms of a one-dimensional effective Hamiltonian, which includes contributions from the nucleobase system, the sugar-phosphate backbone, and the environment. Analytical results for the energy spectrum structure and Landauer conductance of Fibonacci DNA approximants are derived and compared with those corresponding to periodic polyGACT-polyCTGA chains. The main effect of quasiperiodic order is the emergence of a highly fragmented energy spectrum, introducing a characteristic low-energy scale in the electronic structure of aperiodic DNA chains. The presence of a series of high-conductance peaks in the transmission spectra of Fibonacci approximants indicates the existence of extended states in these systems. These results open perspectives for experimental work in nanodevices based on synthetic DNA.
Excitation optical-absorption in self-similar aperiodic lattices
(Physical Review B, 1994) Maciá Barber, Enrique Alfonso; Domínguez-Adame Acosta, Francisco
Exciton optical absorption in self-similar aperiodic one-dimensional systems is considered, focusing our attention on Thue-Morse and Fibonacci lattices as canonical examples. The absorption line shape is evaluated by solving the microscopic equations of motion of the Frenkel-exciton problem on the lattice, in which on-site energies take on two values, according to the Thue-Morse or Fibonacci sequences. Results are compared to those obtained in random lattices with the same stoichiometry and size. We find that aperiodic order causes the occurrence of well-de6ned characteristic features in the absorption spectra, which clearly di8'er from the case of random systems, indicating a most peculiar exciton dynamics. The origin of all the absorption lines is assigned by considering the self-similar aperiodic lattices as composed of two-center blocks, within the same spirit of the renormalization group ideas.
Electrical conductance in duplex DNA: Helical effects and low-frequency vibrational coupling
(Physical review B, 2007) Maciá Barber, Enrique Alfonso
In this work we consider the combined effect of helical structure and base-pair twist motion on charge transfer through duplex DNA at low temperatures. We present a fully analytical treatment of charge-lattice coupled dynamics in terms of nearest-neighbor tight-binding equations describing the propagation of the charge through an effective linear lattice for certain frequency values. The corresponding effective hopping terms include both helicoidal and dynamical effects in a unified way. Although base-pair motion generally reduces pi-pi stack overlapping, the coupling to certain normal modes gives rise to a significant improvement of the Landauer conductance.
Thermal conductivity of one-dimensional Fibonacci quasicrystals
(Physical review B, 2000) Maciá Barber, Enrique Alfonso
We consider a general Fibonacci quasicrystal (FQC) in which both the masses and the elastic constants are aperiodically arranged. Making use of a suitable decimation scheme, inspired by real-space renormalization-group concepts, we obtain closed analytical expressions for the global transfer matrix and transmission coefficient for several resonant critical normal modes. The fractal structure of the frequency spectrum significantly influences both the cumulative contribution of the different normal modes to the thermal transport and the dependence of the thermal conductivity with the temperature over a wide temperature range. The role of resonant effects in the heat transport through the FQC is numerically and analytically discussed.
Three-dimensional effects on the electronic structure of quasiperiodic systems
(Physica B, 1995) Maciá Barber, Enrique Alfonso; Domínguez-Adame Acosta, Francisco
We report on a theoretical study of the electronic structure of quasiperiodic, quasi-one-dimensional systems where fully three-dimensional interaction potentials are taken into account. In our approach, the actual physical potential acting upon the electrons is replaced by a set of nonlocal separable potentials, leading to an exactly solvable Schrodinger equation. By choosing an appropriate trial potential, we obtain a discrete set of algebraic equations that can be mapped onto a general tight-binding-like equation. We introduce a Fibonacci sequence either in the strength of the on-site potentials or in the nearest-neighbor distances, and we find numerically that these systems present a highly fragmented, self-similar electronic spectrum, which becomes singular continuous in the thermodynamical limit. In this way we extend the results obtained so far in one-dimensional models to the three-dimensional case. As an example of the application of the model we consider the chain polymer case.
Physical nature of critical modes in Fibonacci quasicrystals
(Physical review B, 1999) Maciá Barber, Enrique Alfonso
We report on the possibility of modulating the transport properties of critical normal modes in Fibonacci quasicrystals by using the mass ratio as a tuning parameter. The relationship between the spatial structure and the transport properties of these modes is studied analytically in terms of the transmission and Lyapunov coefficients. Power spectrum analysis of the critical modes indicates a complex modulated structure in agreement with previous experimental results, [S0163-1829(99)11337-7].
Physical nature of critical wave functions in Fibonacci systems-Errata (vol 76, pg 2957, 1996)
(Physical review letters, 1997) Maciá Barber, Enrique Alfonso; Domínguez-Adame Acosta, Francisco
Thermal emission control via bandgap engineering in aperiodically designed nanophotonic devices
(Nanomaterials, 2015) Maciá Barber, Enrique Alfonso
Aperiodic photonic crystals can open up novel routes for more efficient photon management due to increased degrees of freedom in their design along with the unique properties brought about by the long-range aperiodic order as compared to their periodic counterparts. In this work we first describe the fundamental notions underlying the idea of thermal emission/absorption control on the basis of the systematic use of aperiodic multilayer designs in photonic quasicrystals. Then, we illustrate the potential applications of this approach in order to enhance the performance of daytime radiative coolers and solar thermoelectric energy generators.