arXiv subjects

L. Martin-Moreno

Publications and source records attributed to L. Martin-Moreno.

48 records · Page 3Linked to original sources

arXiv2003

Enhanced transmission and beaming of light via photonic crystal surface modes

Surface modes are generally believed to be an undesirable feature of finite photonic crystals (PC), unlike point or line defect modes. However, it is possible to make the surface mode radiate by appropriate corrugation of the PC interface. In this paper we show theoretically that the coherent action of these surface indentations can be engineered to collimate within a few degrees the light exiting a PC waveguide, or to funnel light coming from free space into the waveguide.

cond-mat↗

arXiv2003

Theory of Plasmon-assisted Transmission of Entangled Photons

The recent surface plasmon entanglement experiment [E. Altewischer et al., Nature (London) 418, 304 (2002)] is theoretically analyzed. The entanglement preservation upon transmission in the non-focused case is found to provide information about the interaction of the biphoton and the metallic film. The entanglement degradation in the focused case is explained in the framework of a fully multimode model. This phenomenon is a consequence of the polarization-selective filtering behavior of the metallic nanostructured film.

quant-ph↗

arXiv2002

Chessboard magnetoconductance of a quantum dot in the Kondo regime

Transport through a quantum dot (QD) in the Kondo regime shows alternating regions of high and low conductance when both an external magnetic field and the gate potential controlling the depth of the QD potential are varied. We present a theoretical analysis of this chessboard aspect of the magneto-conductance. An effective Kondo Hamiltonian is obtained by means of a restriction to the Hilbert space supported by just a few low energy states of N and N(+/-)1 electrons in the QD. We obtain antiferromagnetic exchange couplings depending on tunneling amplitudes and correlation effects. When either the magnetic field or the number of electrons in the QD is varied, Kondo temperature shows large oscillations due to the successive appearance of ground states having strong and weak correlation effects alternatively.

cond-mat.mes-hall↗

arXiv2000

Kondo effect in multielectron quantum dots at high magnetic fields

We present a general description of low temperature transport through a quantum dot with any number of electrons at filling factor $1<ν<2$. We provide a general description of a novel Kondo effect which is turned on by application of an appropriate magnetic field. The spin-flip scattering of carriers by the quantum dot only involves two states of the scatterer which may have a large spin. This process is described by spin-flip Hubbard operators, which change the angular momentum, leading to a Kondo Hamiltonian. We obtain antiferromagnetic exchange couplings depending on tunneling amplitudes and correlation effects. Since Kondo temperature has an exponential dependence on exchange couplings, quantitative variations of the parameters in different regimes have important experimental consequences. In particular, we discuss the {\it chess board} aspect of the experimental conductance when represented in a grey scale as a function of both the magnetic field and the gate potential affecting the quantum dot.

cond-mat.mes-hall↗

arXiv2000

Theory of extraordinary optical transmission through subwavelength hole arrays

We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interfaces. Different regimes of tunneling (resonant through a ''surface plasmon molecule", or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system.

cond-mat.mtrl-sci↗

arXiv2000

Canted ground state in artificial molecules at high magnetic fields

We analyze the transitions that a magnetic field provokes in the ground state of an artificial homonuclear diatomic molecule. For that purpose, we have performed numerical diagonalizations for a double quantum dot around the regime of filling factor 2. We present phase diagrams in terms of tunneling and Zeeman couplings, and confinement strength. We identify a series of transitions from ferromagnetic to symmetric states through a set of canted states with antiferromagnetic couping between the two quantum dots.

cond-mat.mes-hall↗

arXiv1999

Spin-isospin textured excitations in a double layer at filling factor $ν=2$

We study the charged excitations of a double layer at filling factor 2 in the ferromagnetic regime. In a wide range of Zeeman and tunneling splittings we find that the low energy charged excitations are spin-isospin textures with the charge mostly located in one of the layers. As tunneling increases, the parent spin texture in one layer becomes larger and it induces, in the other layer, a shadow spin texture antiferromagnetically coupled to the parent texture. These new quasiparticles should be observable by measuring the strong dependence of its spin on tunneling and Zeeman couplings.

cond-mat.mes-hall↗

arXiv1998

Self-Assembled Triply Periodic Minimal Surfaces as moulds for Photonic Band Gap Materials

We propose systems with structures defined by self-assembled triply periodic minimal surfaces (STPMS) as candidates for photonic bandgap materials. To support our proposal we have calculated the photonic bands for different STPMS and we have found that, at least, the double diamond and gyroid structures present full photonic bandgaps. Given the great variety of systems which crystalize in these structures, the diversity of possible materials that form them and the range of lattice constants they present, the construction of photonic bandgap materials with gaps in the visible range may be presently within reach.

cond-mat.mtrl-sci↗

arXiv1995

Skyrmions and edge spin excitations in quantum Hall droplets

We present an analysis of spin-textures in Quantum Hall droplets, for filling factors $ν\simeq 1$. Analytical wavefunctions with well defined quantum numbers are given for the low-lying states of the system which result to be either bulk skyrmions or edge spin excitations. We compute dispersion relations and study how skyrmions become ground states of the Quantum Hall droplet at $ν\gtrsim 1$. A Hartree-Fock approximation is recovered and discussed for those spin textures.

cond-mat↗

arXiv1994

Low-lying excitations of Quantum Hall Droplets

We present the adequate circular representation of charge density excitations in Quantum Hall droplets at filling factor 1. A novel set of operators describes magnetoexcitons with well defined both total and center-of-mass angular momentum. The accuracy of this description is shown by the high overlap of the magnetoexcitons with the exact eigenstates of a quantum dot in a magnetic field obtained from numerical calculations up to 20 electrons. From such magnetoexcitons we get a good understanding of total energies and spectral functions.

cond-mat↗

arXiv1994

Capacitance spectroscopy in quantum dots: Addition spectra and decrease of tunneling rates

A theoretical study of single electron capacitance spectroscopy in quantum dots is presented. Exact diagonalizations and the unrestricted Hartree-Fock approximation have been used to shed light over some of the unresolved aspects. The addition spectra of up to 15 electrons is obtained and compared with the experiment. We show evidence for understanding the decrease of the single electron tunneling rates in terms of the behavior of the spectral weight function. (To appear in Phys. Rev. B (Rapid Comm.))

cond-mat↗

arXiv1993

Correlation Effects on Transport Through Few-Electrons Systems

We study lateral tunneling through a quantum box including electron-electron interactions in the presence of a magnetic field which breaks single particle degeneracies. The conductance at zero temperature as a function of the Fermi energy in the leads consists of a set of peaks related to changing by one the electron occupancy in the box. We find that the position and heights of the peaks are controlled by many-body effects. We compute the conductance up to 8 electrons for several cases where correlation effects dominate. In the range of intermediate fields spin selection rules quench some peaks. At low and high fields the behavior of the conductance as a function of the number of electrons is very different due to big changes in the many-body ground state wavefunctions.

cond-mat↗