Enrique Muñoz

Quantum heat engine in the relativistic limit: the case of a Dirac particle.

We studied the efficiency of two different schemes for a quantum heat engine, by considering a single Dirac particle trapped in an infinite one-dimensional potential well as the working substance. The first scheme is a cycle, composed of two adiabatic and two isoenergetic reversible trajectories in configuration space. The trajectories are driven by a quasistatic deformation of the potential well due to an external applied force. The second scheme is a variant of the former, where isoenergetic trajectories are replaced by isothermal ones, along which the system is in contact with macroscopic thermostats. This second scheme constitutes a quantum analog of the classical Carnot cycle. Our expressions, as obtained from the Dirac single-particle spectrum, converge in the nonrelativistic limit to some of the existing results in the literature for the Schrödinger spectrum.

Analytic approach to magneto-strain tuning of electronic transport through a graphene nanobubble: perspectives for a strain sensor

We consider the scattering of Dirac particles in graphene due to the superposition of an external magnetic field and mechanical strain. As a model for a graphene nanobubble, we find exact analytical solutions for single-particle states inside and outside a circular region submitted to the fields. Finally, we obtain analytical expressions for the scattering cross-section, as well as for the Landauer current through the circular region. Our results provide a fully-analytical treatment for electronic transport through a graphene nanobubble, showing that a combination of a physical magnetic field and strain leads to valley polarization and filtering of the electronic current. Moreover, our analytical model provides an explicit metrology principle to measure strain by performing conductance experiments under a controlled magnetic field imposed over the sample.

Conductance scaling in Kondo-correlated quantum dots: Role of level asymmetry and charging energy

The low temperature electrical conductance through correlated quantum dots provides a sensitive probe of the physics (e.g., of Fermi-liquid vs non-Fermi-liquid behavior) of such systems. Here, we investigate the role of level asymmetry (gate voltage) and local Coulomb repulsion (charging energy) on the low temperature and low field scaling properties of the linear conductance of a quantum dot described by the single level Anderson impurity model. We use the numerical renormalization group to quantify the regime of gate voltages and charging energies where universal Kondo scaling may be observed and also quantify the deviations from this universal behavior with increasing gate voltage away from the Kondo regime and with decreasing charging energy. We also compare our results with those from a recently developed method for linear and non-linear transport, which is based on renormalized perturbation theory using dual fermions, finding excellent agreement at particle-hole symmetry and for all charging energies and reasonable agreement at small finite level asymmetry. Our results could be a useful guide for detailed experiments on conductance scaling in semiconductor and molecular quantum dots exhibiting the Kondo effect.

Symmetries of relativistic world lines

Symmetries are essential for a consistent formulation of many quantum systems. In this paper we discuss a previously unnoticed symmetry, which is present for any Lagrangian term that involves

The stepwise path integral of the relativistic point particle

dot{x}^2

The renormalized superperturbation theory (rSPT) approach to the Anderson model in and out of equilibrium

. As a basic model that incorporates the fundamental symmetries of quantum gravity and string theory, we consider the Lagrangian action of the relativistic point particle. A path integral quantization for this seemingly simple system has for long presented notorious problems. Here we show that those problems are overcome by taking into account the newly discovered additional symmetry, leading directly to the exact Klein-Gordon propagator.

¡Defendamos Díchato! Bienes comunes y conflicto territorial en los espacios litorales chilenos

In this paper we present a stepwise construction of the path integral over relativistic orbits in Euclidean spacetime. It is shown that the apparent problems of this path integral, like the breakdown of the naive Chapman–Kolmogorov relation, can be solved by a careful analysis of the overcounting associated with local and global symmetries. Based on this, the direct calculation of the quantum propagator of the relativistic point particle in the path integral formulation results from a simple and purely geometric construction.

Nonlinear Thermoelectric Response of Quantum Dots: Renormalized Dual Fermions Out of Equilibrium

The properties of current-carrying steady states of strongly correlated systems away from the linear-response regime are of topical interest. In this article, we review the renormalized perturbation theory, or renormalized SPT of reference [1] for the Anderson model. We present an extension to higher orders and compare the higher-order results with NRG calculations. Finally, we elucidate the role of Ward identities in calculating out-of-equilibrium properties and address claims made in the literature.

The effect of electron scattering from disordered grain boundaries on the resistivity of metallic nanostructures

espanolRESUMEN El Codigo Civil de la Republica de Chile establecio que los pescadores podian hacer uso de las playas del mar para sus labores de pesca, definiendo de este modo un espacio litoral de uso comun independiente de los propietarios aledanos que pronto se transformaria en un territorio de conflicto que se incrementaria en la medida que distintas actividades economicas se fueron superponiendo en estos espacios comunes. En este articulo presentamos algunos ejemplos historicos que reflejan como los pescadores utilizaron este derecho en defensa de sus intereses relevando, especialmente, el caso del borde costero de Dichato que poco antes de mediados del siglo XX fue el escenario de un conflicto que involucro al Estado, los propietarios, los pescadores y los veraneantes. EnglishABSTRACT The Civil Code of the Republic of Chile established that fishermen could make use of the sea beaches for their fishing activities, thereby defining a coastline space of independent common use for the neighboring owners, who would soon become a territory of conflict that would increase to the extent that different economic activities were superimposed on these common spaces. This paper presents some historical examples that reflect how fishermen used this right to defend their interests. Special atention is given to the case of the coastal edge of Dichato, shortly before it were the scene of a conflict involving the State, owners, fishermen and vacationers in the mid-twentieth century.

Strain-induced chiral symmetry breaking leads to large Dirac cone splitting in graphene/graphane heterostructure

The thermoelectric transport properties of nanostructured devices continue to attract attention from theorists and experimentalist alike as the spatial confinement allows for a controlled approach to transport properties of correlated matter. Most of the existing work, however, focuses on thermoelectric transport in the linear regime despite the fact that the nonlinear conductance of correlated quantum dots has been studied in some detail throughout the last decade. Here, we review our recent work on the effect of particle-hole asymmetry on the nonlinear transport properties in the vicinity of the strong coupling limit of Kondo-correlated quantum dots and extend the underlying method, a renormalized superperturbation theory on the Keldysh contour, to the thermal conductance in the nonlinear regime. We determine the charge, energy, and heat current through the nanostructure and study the nonlinear transport coefficients, the entropy production, and the fate of the Wiedemann-Franz law in the non-thermal steady-state. Our approach is based on a renormalized perturbation theory in terms of dual fermions around the particle-hole symmetric strong-coupling limit.