arXiv subjects

C. A. Balseiro

Publications and source records attributed to C. A. Balseiro.

At least 73 records · Page 4Linked to original sources

arXiv2004

On the Magnetic Nature of Quantum Point Contacts

We present results for a model that describes a quantum point contact. We show how electron-electron correlations, within the unrestricted Hartree-Fock approximation, generate a magnetic moment in the point contact. Having characterized the magnetic structure of the contact, we map the problem onto a simple one-channel model and calculate the temperature dependence of the conductance for different gate voltages. Our results are in good agreement with experimental results obtained in GaAs devices and support the idea of Kondo effect in these systems.

cond-mat.mes-hall↗

arXiv2004

Quantum corral wave function engineering

We present a theoretical method for the design and optimization of quantum corrals with specific electronic properties. Taking advantage that spins are subject to a RKKY interaction that is directly controlled by the scattering of the quantum corral, we design corral structures that reproduce spin Hamiltonians with coupling constants determined a priori. We solve exactly the two-dimensional electron gas scattering problem for each corral configuration within the effective mass approximation and s-wave scattering using a Green function method. Subsequently, the geometry of the quantum corral is optimized with an algorithm that combines simulated annealing and genetic approaches. We demonstrate that it is possible to automatically design quantum corrals with complicated target electronic properties, such as multiple mirages with predefined relative intensities at specific locations. In addition we design structures that are particularly sensitive to the phase shift of impurities at certain positions allowing the measurement of the value of this parameter on the copper surface.

cond-mat.mes-hall↗

arXiv2004

Theory of Edge States in Systems with Rashba Spin-Orbit Coupling

We study the edge states in a two dimensional electron gas with a transverse magnetic field and Rashba spin-orbit coupling. In the bulk, the interplay between the external field perpendicular to the gas plane and the spin-orbit coupling leads to two branches of states that, within the same energy window, have different cyclotron radii. For the edge states, surface reflection generates hybrid states with the two cyclotron radii. We analyze the spectrum and spin structure of these states and present a semiclassical picture of them.

cond-mat.mes-hall↗

arXiv2004

Transverse Electron Focusing in Systems with Spin-Orbit Coupling

We study the transverse electron focusing in a two dimensional electron gas with Rashba spin-orbit coupling. We show that the interplay between the external magnetic field and the spin-orbit coupling gives two branches of states with different cyclotron radius within the same energy window. This effect generates a splitting of the first focusing peak in two contributions. Each one of these contributions is spin polarized. The surface reflection mixes the two branches and the second focusing peak does not present the same effect. While for GaAs/AlGaAs heterostructures the effect is small, in systems like InSb/InAlSb the effect should be clearly observed.

cond-mat.mes-hall↗

arXiv2004

Simulations of Dynamical Ordering in Pinned Vortex Systems

We model a vortex system in a sample with bulk pinning and superficial pinning generated by a magnetic decoration. We perform a sequence of finite temperature numerical experiments in which external forces are applied to obtain a dynamically ordered vortex lattice. We analyze the final structures and the behavior of the total energy of the system.

cond-mat.supr-con↗

arXiv2002

STM conductance of Kondo impurities on open and structured surfaces

We study the scanning tunneling microscopy response for magnetic atoms on open and structured surfaces using Wilson's renormalization group. We observe Fano resonances associated with Kondo resonances and interference effects. For a magnetic atom in a quantum corral coupled to the confined surface states, and experimentally relevant parameters, we observe a large confinement induced effect not present in the experiments. These results suggest that the Kondo screening is dominated by the bulk electrons rather than the surface ones.

cond-mat.mes-hall↗

arXiv2002

Transport through quantum dots in mesoscopic circuits

We study the transport through a quantum dot, in the Kondo Coulomb blockade valley, embedded in a mesoscopic device with finite wires. The quantization of states in the circuit that hosts the quantum dot gives rise to finite size effects. These effects make the conductance sensitive to the ratio of the Kondo screening length to the wires length and provide a way of measuring the Kondo cloud. We present results obtained with the numerical renormalization group for a wide range of physically accessible parameters.

cond-mat.mes-hall↗

arXiv2002

Spectral densities of Kondo impurities in nanoscopic systems

We present results for the spectral properties of Kondo impurities in nanoscopic systems. Using Wilson's renormalization group we analyze the frequency and temperature dependence of the impurity spectral density for impurities in small systems that are either isolated or in contact with a reservoir. We have performed a detailed analysis of the structure of the impurity spectral density for energies around the Fermi energy for different Fermi energies relative to the intrinsic structure of the local density of states. We show how the electron confinement energy scales introduce new features in the frequency and temperature dependence of the impurity spectral properties.

cond-mat.mes-hall↗

arXiv2002

Spin-orbit coupling and ESR theory for carbon nanotubes

A theoretical description of ESR in 1D interacting metals is given, with primary emphasis on carbon nanotubes. The spin-orbit coupling is derived, and the resulting ESR spectrum is analyzed by field theory and exact diagonalization. Drastic differences in the ESR spectra of single-wall and multi-wall nanotubes are found. For single-wall tubes, the predicted double peak spectrum could reveal spin-charge separation.

cond-mat.str-el↗

arXiv2002

Kondo impurities in nanoscopic systems: new confinement-induced regimes

We present results for Kondo impurities in nanoscopic systems. Using exact diagonalization in small clusters and Wilson's renormalization group we analyze an isolated system and a nanoscopic system weakly coupled to a macroscopic reservoir. In the latter case, new regimes not observed in macroscopic homogeneous systems are induced by the confinement of conduction electrons. These new confinement-induced regimes are very different depending on whether the Fermi energy coincides with the energy of a resonant state or lies between two quasi-bound states.

cond-mat.mes-hall↗

arXiv2001

Quasiparticles and c-axis coherent hopping in high T_c superconductors

We study the problem of the low-energy quasiparticle spectrum of the extended t-J model and analyze the coherent hopping between weakly coupled planes described by this model. Starting with a two-band model describing the Cu-O planes and the unoccupied bands associated to the metallic atoms located in between the planes, we obtain effective hopping matrix elements describing the c-axis charge transfer. A computational study of these processes shows an anomalously large charge anisotropy for doping concentrations around and below the optimal doping.

cond-mat.str-el↗

arXiv2001

Mirages and enhanced magnetic interactions in quantum corrals

We develop a theory for the interactions between magnetic impurities in nanoscopic systems. The case of impurities in quantum corrals built on the (111) Cu surface is analyzed in detail. For elliptical corrals with one impurity, clear magnetic mirages are obtained. This leads to an enhancement of the inter-impurity interactions when two impurities are placed at special points in the corral. We discuss the enhancement of the conduction electron response to the local perturbation in other nanoscopic systems.

cond-mat↗

arXiv2001

Spectroscopic and magnetic mirages of impurities in nanoscopic systems

We present exact results for magnetic impurities in nanoscopic systems with focusing properties. We analyze the spectroscopic and magnetic properties of Kondo, intermediate valence and magnetic impurities on a sphere with a metallic surface. Exact calculations show the occurrence of spectroscopic and magnetic mirages at the antipodes of the impurity location. Comparison with calculations performed using effective models validates previous calculations of spectroscopic mirages. Our results can be extended to other systems with focusing properties like quantum corrals.

cond-mat↗

arXiv2000

Transport properties and structures of vortex matter in layered superconductors

In this paper we analyze the structure, phase transitions and some transport properties of the vortex system when the external magnetic field lies parallel to the planes in layered superconductors. We show that experimental results for resistivity are qualitatively consistent with numerical simulations that describe the melting of a commensurate rotated lattice. However for some magnetic fields, the structure factor indicates the occurrence of smectic peaks at an intermediate temperature regime.

cond-mat.supr-con↗

arXiv1999

Freezing transition of the vortex liquid in anisotropic superconductors

We study the solid-liquid transition of a model of pancake vortices in laminar superconductors using a density functional theory of freezing. The physical properties of the system along the melting line are discussed in detail. We show that there is a very good agreement with experimental data in the shape and position of the first order transition in the phase diagram and in the magnitude and temperature dependence of the magnetic induction jump at the transition. We analyze the validity of the Lindemann melting criterion and the Hansen-Verlet freezing criterion. Both criteria are shown to be good to predict the phase diagram in the region where a first order phase transition is experimentally observed.

cond-mat.supr-con↗

arXiv1999

Slave fermion theory of confinement in strongly anisotropic systems

We present a mean field treatment of a strongly correlated model of electrons in a three-dimensional anisotropic system. The mass of the bare electrons is larger in one spatial direction (the c-axis direction), than in the other two (the ab-planes). We use a slave fermion decomposition of the electronic degrees of freedom and show that there is a transition from a deconfined to a confined phase in which there is no coherent band formation along the c-axis.

cond-mat.str-el↗

arXiv1997

Universalities in vortex transport at the melting transition

We consider the jump in resistance at the melting transition, which is experimentally observed to be constant, independent of magnetic field (vortex density). We present an explanation of this effect based on vortex cuttings, and universalities of the structure factor at the freezing transition (the Hansen-Verlet criterion).

cond-mat.supr-con↗

arXiv1997

Dynamics of d-wave Vortices: Angle-Dependent Nonlinear Hall Effect

We study the dynamics of vortices in d-wave superconductors using a phenomenological time-dependent Ginzburg-Landau equation with mixing of s- and d-wave components. We present numerical simulations under an external driving current $J$ oriented with an angle $ϕ$ with respect to the $b$ crystal axis, calculating the vortex motion and induced electric fields for $κ=\infty$. We find an intrinsic Hall effect for $ϕ\neq 0$ which depends as $\sim\sin(4ϕ)$, and increases non-linearly with $J$.

cond-mat.supr-con↗