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 26

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.
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.
π -π orbital resonance in twisting duplex DNA: Dynamical phyllotaxis and electronic structure effects
(Physical review B, 2009) Maciá Barber, Enrique Alfonso
The presence of synchronized, collective twist motions of the Watson-Crick base pairs in DNA duplexes (helicoidal standing waves) can efficiently enhance the pi-pi orbital overlapping between nonconsecutive base pairs via a long-range, phonon-correlated tunneling effect. The resulting structural patterns are described within the framework of dynamical phyllotaxis, providing a realistic treatment which takes into account both the intrinsic three-dimensional, helicoidal geometry of DNA, and the coupling between the electronic degrees of freedom and double-helix DNA molecular dynamics at low frequencies. The main features of the resulting electronic band structures are discussed for several resonance frequencies of interest, highlighting the possible biophysical implications of the obtained results.
Modeling the spectral conductivity of Al-Mn-Si quasicrystalline approximants: A phenomenological approach
(Physical review B, 2005) Maciá Barber, Enrique Alfonso; Takeuchi, Tsunehiro; Otagiri, Toshio
The electronic structure of a quasicrystalline approximant sample is analyzed by means of a combined study of different experimental transport curves within a phenomenological approach. The main features of the obtained spectral conductivity are discussed and compared to those corresponding to icosahedral quasicrystals. Such a comparison provides interesting clues about the role of quasiperiodic order and of local atomic arrangements in the origin of unusual behaviors in the electrical conductivity and thermopower observed in complex metallic alloys.
DNA-based thermoelectric devices: a theoretical prospective
(Physical review B, 2007) Maciá Barber, Enrique Alfonso
The thermoelectric performance of PolyG-PolyC and PolyA-PolyT double-stranded chains connected between organic contacts at different temperatures is theoretically studied on the basis of an effective model Hamiltonian. The obtained analytical expressions reveal the existence of important resonance effects leading to a significant enhancement of the Seebeck coefficient depending on the Fermi level position. High thermoelectric power factors, up to P=(1.5-3)x10^(-3) W m^(-1) K^(-2), are obtained close to the resonance energy. These values suggest that significantly high values of the thermoelectric figure of merit may be attained for synthetic DNA samples at room temperature. The possibility of combining p-type and n-type synthetic DNA chains in the design of a nanoscale Peltier cell is discussed, taking into account both contact and environmental effects.
Thermoelectric figure of merit of AlPdRe icosahedral quasicrystals: composition-dependent effects
(Physical review B, 2004) Maciá Barber, Enrique Alfonso
In this work we present a theoretical study on the composition dependence of the thermoelectric figure of merit (ZT) of icosahedral AlPdRe quasicrystals. From our study we conclude that band-structure effects play a significant role in determining the thermoelectric performance of these alloys. By comparing our analytical results with available experimental data of transport coefficients we discuss the most appropriate stoichiometries for thermoelectric applications, concluding that (i) those samples whose Fermi level is located at the pseudogap's minimum exhibit very small ZT values, and (ii) relatively large ZT values are expected for those samples exhibiting narrow features in the density of states close to the Fermi level.
Long range correlations in DNA: scaling properties and charge transfer efficiency
(Physical review letters, 2003) Roche, S.; Bicout, D.; Maciá Barber, Enrique Alfonso; Kats, E.
We address the relation between long-range correlations and charge transfer efficiency in aperiodic artificial or genomic DNA sequences. Coherent charge transfer through the highest occupied molecular orbital states of the guanine nucleotide is studied using the transmission approach, and the focus is on how the sequence-dependent backscattering profile can be inferred from correlations between base pairs.
Modeling the electrical conductivity of icosahedral quasicrystals
(Physical review B, 2000) Maciá Barber, Enrique Alfonso
A model for the electronic structure of icosahedral quasicrystals is proposed on the basis of a number of pertinent experimental results. From this model we obtain a closed analytical expression for the electrical conductivity accurately describing the most remarkable features observed in the sigma(T) curves of high quality quasicrystals. As a convenient working example we compare the theoretical description provided by our treatment with a series of suitable experimental data for the i-AlCuRu, unveiling a relationship among the density-of-states structure, the sample stoichiometry, and the electrical conductivity of different samples at different temperature ranges.
Thermal conductivity in complex metallic alloys: Beyond Wiedemann-Franz law
(Physical review B, 2009) Maciá Barber, Enrique Alfonso
In this work we consider the range of validity of the Wiedemann-Franz law (WFL) in quasicrystals, approximant phases, and giant unit-cell complex metallic alloys. In the limit of very low temperatures the WFL is satisfied, as expected, but as the temperature is progressively increased the Lorenz function deviates from the ideal behavior L(T)/L₀=1. Whereas the quasicrystalline sample exhibits a systematic and significant deviation for all considered temperatures, the other samples show the existence of a characteristic temperature signaling the onset of the anomalous behavior. This characteristic temperature is directly related to the unit-cell density of the sample and progressively takes on larger values as this density decreases. An alternative route to derive the lattice contribution to the thermal conductivity based on a simultaneous fitting analysis of the electrical conductivity sigma(T) and thermoelectric-power S(T) experimental transport curves is proposed. The capabilities of this approach are illustrated by studying the temperature dependence of the lattice contribution to the thermal conductivity in the (xi)'-AlPdMn giant unit-cell phase.