PROPERTIES IN TRANSPORT OF ELECTRONS

Author: GARATE ZUBIAURRE GORKA.
Year: 2004.
University: PAÍS VASCO [www.ehu.es].
Place of defense: E.T.S. DE INGENIERIA DE BILBAO.
Place of preparation: E.T.S. DE INGENIERIA DE BILBAO.

Summary: The work has focused on the development of an application of finite element to forecast for acoustic noise and vibration levels in the interior and exterior of mechanical systems compounds half structural, fluid and absorbing sound porous. It develops the specific wording of each of the media, and all the case studies of links between them. Included are examples of validation for the entire design, with contrastaciones analytical and experimental.

Author: GOMEZ NAVARRO GONZALEZ CRISTINA.
Year: 2005.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: DEPARTAMENTO DE FISICA DE LA MATERIA CONDENSADA.
Place of preparation: FACULTAD DE CIENCIAS,.

Author: PRIOR ARCE JAVIER.
Year: 2005.
University: MURCIA [www.um.es].
Place of defense: FACULTAD DE QUÍMICAS, SECCIÓN DE FÍSICA.
Place of preparation: FACULTAD DE QUÍMICA.

Summary: It has become a study of conductance in the localized regime in the absence of interaction between electrons. Specifically, they have studied the dependence of the variance of the logarithm of the conductance with the size of L system, in both two-dimensional and three-dimensional systems, and the cumulantes higher-order Check distribution of the logarithm of conductance is not in the Gaussian systems. The variance of the logarithm of the conductance depends on the length L of the system as L risen to 2 / 3 in two-dimensional systems and L risen to 2 / 5 in three-dimensional systems. It has also been studied violation of the theory of scale for energy corresponding to the tail of the density of states in two-dimensional systems. This is because the distance between the states is of the order of the length of location. In this region it is necessary to define a second parameter of scale to adequately describe the properties of the distribution of the logarithm of the conductance. Demonstration of the universality of the prefactor g0 of conductance. This parameter is not affected by the disorder of the system or the Fermi energy. It also has studied the intersection of regime located diffusive regime for two-dimensional systems. The results suggest that the distribution of conductance is apparently Gaussian for the values of conductance greater than approximately one and log-normal for the values lower than one. It proposes a model that describes the logarithmic corrections to the law on Mott in one-dimensional systems and presents difficulties that arise in calculating the length of location. When the system size is not very big found significant discrepancies between the values of the elements of the matrix and conductance at zero temperature for both one-dimensional and two-dimensional systems. The disorder caused by the quantum fluctuations are as important as those due to geometrical disorder. The first increase in importance according decreases the temperature of the system.

Author: Prada Núñez Elsa.
Year: 2005.
University: AUTÓNOMA DE MADRID [www.uam.es].
Place of defense: DpTO. Fís. Teór.de la Materia Condensada.
Place of preparation: Dpto. de Física de la Materia Condensada.

Summary: There is a phenomenon in quantum mechanics without similar classic called "interlocking" which it is possible to prepare two particles in a state such that it can not be described as the direct product of the state of individual particles, no matter how far are spatially find one another. This kind of non-local quantum correlations can be used as a resource physicist in the field of quantum information, for example, to perform quantum teleportation. In particular, pairs of electrons with spin intertwining of non-local could be used in the future for communication tasks in quantum computers based on quantum physics in the solid state. In this thesis we considered three important aspects related to them. First we have studied the problem of how to generate these pairs Einstein-Podolsky-Rosen (RPA). We have obtained a Hamiltoniano tunnel that allows local investigate transport across interfaces arbitrary geometry and finite size. With him we have analyzed the issuance of Cooper pairs from a superconducting to normal two metals through two small tunnel contacts separated a distance r. This device could be used as a "entrelazador", or even a source of RPA, since electrons have issued a state of spin intertwined, in particular type singlet. To avoid the problem of the rapid decay of this flow with r, we have proposed a new mechanism to separate electrons intertwined that makes use of normal resonances and Andreev in a structure superconductor-doble barrera-gas two-dimensional electron (2DEG). This entrelazador is based on a filter angle that generates beams of electrons intertwined divergent not locally. In a second part we considered the problem of the evolution of these pairs intertwined within the nanoestructura when they are subjected to decoherencia. To simulate processes suffered by inelastic electron we used a model called phenomenological probe voltage. Specifically, we have this generalized model for incidents that may include statements that have a conservation with intertwining arbitrary loads instantly. Finally, we have addressed the problem of detecting intertwining using two different techniques. On the one hand we considered violation of the inequality of Clauser-Horne expressed in terms of statistics complete count of electrons in a conductor multiterminal mesoscópico. We esncontrado existing system parameters for which the violation is maintained in the presence of a decoherencia arbitrarily large, which could be used in the design of a device to conduct pilot tests with Bell electrons. On the other hand we have analyzed measures of shot noise in one of the threads out of a geometry divider beams four arms attached to a entrelazador. With this method it is possible to detect intertwining and discriminate between different types of incoming states, as states singlet, hat trick, or blends classical statistics spin up and spin down. In particular, we have found that this detection scheme is robust in the presence of decoherencia until inelastic scattering probabilities of 50 percent.

Author: RODRIGUEZ GONZALEZ ALBERTO.
Year: 2005.
University: SALAMANCA [www.usal.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: Technological advances have enabled the fabrication of semiconductor devices for which you can select at will some of its properties and whose small harbor only a few tens of atoms. These structures can be designed to control the dimensionality of confinement of carriers in the material: two-dimensional electronic gas, one-dimensional quantum wires and quantum dots. These systems require a low dimensionality formalism appropriate theoretical different from that used at macrocópica, because at this level the properties of matter are essentially determined by rules mecánico-cuánticas. In particular, to carry out the characterization of the electronic properties of such systems is an important element to consider is the presence of disorder, as it plays a key role in the transport processes. In this paper we study the electronic properties of one-dimensional disordered systems.