Jaime Keller

Anisotropy of optical and transport properties in the a-b plane of the high temperature superconductor YBa2Cu4O8

Abstract The anisotropy within the a-b plane of YBa2Cu4O8 has been studied on single crystal platelets by optical and electron transport measurements. The optical investigations include polarized reflectivity measurements at room temperature for photon energies between 0.5 and 4 eV and a direct measurement of the ratio of the reflectivity coefficients r b r a . The anisotropy of the electrical resistivity has been determined from AC van der Pauw measurements using the Montgomery formalism for anisotropic materials. The optical reflectivity spectra are dominated by Drude-like free electron contributions with plasmon energies of 2.8 eV and 1.67 eV for the electrical field vector along the b- and a-axis, respectively. The electrical resistivity displays an anisotropy of a factor of about 3. The superconducting transition temperature (midpoint of the resistivity drop) is 76 K. Contrary to YBa2Cu3O7, clear deviations from linear temperature dependences of the resistivity are observed in the normal state of YBa2Cu4O8. An extrapolation of the linear (normal) part gives zero resistance at 36 ± 2 K and not 0 K. The observed anisotropies are compared with results of a tight binding calculation.

Density Functional Theory

The constrained search approach, mappings to external potentials, and virial-like theorems for electron-density and one-matrix energy-functional theories.- Density matrices, reduced density matrices, a geometric investigation of their properties, and applications to density functional theory.- Properties of one-matrix energy functionals.- Self-interaction correction.- Some recent developments in density functional theory.- Electron gas models and density functional theory.- Electron structure calculations for heavy atoms: A local density approach.- Density functionals obtained from models of the electron first and second order density matrices.- Free energy density functionals for non-uniform classical fluids.

Spinors and multivectors as a unified tool for spacetime geometry and for elementary particle physics

From the definition of spinors as the minimal left (right) modules of multivectors (that is, of vectors and their outer products), we can construct a unified mathematical approach for the study of matter and its interaction fields, which are either defined as fields in the geometrical spacetime or considered as generators of the physical spacetime. It is also shown how matter and interaction fields can be represented either by spinor fields or by multivector fields, both types of fields carrying the same information as the traditional corresponding spinors, vectors, or tensors. Geometry is more transparent in one representation (multivector form), and physics is more obvious in the spinor representation. Our theory provides a unified and totally self-consistent representation of quarks (barions), leptons, and all their known interactions.

Multivectorial representation of Lie groups

In vector spaces of dimensionn=p+q a multivector (Clifford) algebraC(p, q) can be constructed. In this paper a multivectorC(p, q) representation, riot restricted to the bivector subalgebraC2(p, q), is developed for some of the Lie groups more frequently used in physics. This representation should be especially useful in the special cases of (grand) unified gauge field theories, where the groups used do not always have a simple tensor representation.

Ethyl and methylphenylcarbamates as antihelmintic agents: theoretical study for predicting their biological activity by PM3

Abstract PM3 calculations have been carried out on alkyl 4-(R)-phenylcarbamates and benzimidazole compounds in order to identify electronic features similitude using Principal Component Analysis, Canonic Analysis, stepwise Multiple Regression and Cluster Analysis. We have been able to establish a trend to predict antihelmintic activity for the best candidates of alkyl 4-(R)-phenylcarbamates.

Space-time dual geometry theory of elementary particles and their interaction fields

The important role of the operator γ5 in the physics of elementary particles and their interactions is considered basic in this paper where it is shown that it corresponds to the duality rotation in space-time and how the dual geometry can be used to consider new symmetries for the wave equations of particles and their interaction fields. The new set of symmetries is shown to exactly correspond to what is needed to find the known schemes of leptons and quarks and to be the origin of many of the properties which are found expermentally for these elementary particles.

A multivectorial Dirac equation

The multivectorial generalization of the Cartan map, for C(1,3) space‐time Clifford algebra and an arbitrary gauge group in an isotopic space, is applied to the standard Dirac equation to generate the multivectorial Dirac equation. Using both geometrical and physical reasoning, a particular case discussed by Reifler and Morris [J. Math. Phys. 26, 2059 (1985)] is projected from the general multivectorial Dirac equation, to discuss the properties and limitations associated to their quaternion model. The use of the general multivectorial Dirac equation, which can be defined on any space‐time manifold, is also illustrated.

Cluster methods to study the electronic structure of condensed matter

Multiple scattering techniques have been used to study the electronic states (core and continuum states) of condensed matter. The electronic density of states, total energies, charge and spin densities are computed self consistently. The electronic and magnetic properties of the materials are evaluated from this results. The model material is a finite cluster of atoms immersed in the spherical average potential of the rest of the system. The electronic states are then either core states or continuum states. Examples in which the wave functions are given molecular boundary conditions far from the cluster of atoms are also presented.

Wave Equation of Symmetry Constrained Dirac Particles

Starting from the energy-momentum vector relationship for two observers, a multivector wave equation, which we call the full Dirac equation, is derived. It is shown to correspond to a series of symmetry constrained Dirac Fields with basic, repetitive,SU(5) structure. The consequences of the symmetry restrictions for the definition of charge, hypercharge, color, charm, etc, are discussed together with a description of the associated gauge fields.

Multivectorial generalization of the Cartan map

A multivectorial generalization of the spinors to vectors Cartan map is constructed, with space‐time as a base space, constructed from spinors (Dirac spinors and spinors pairs being particular cases) onto a multivector space with two internal symmetries: one of them is the fundamental space‐time Clifford group C(1,3) and the other an ‘‘isotopic space’’ (in multivectorial representation) related with the more common gauge groups. The algebraic properties of this map and of the operators representing observables are studied. The inversion map is also presented. The quaternion projection of the map is shown as are its properties and its mathematical and physical meaning. The procedure presented here is compared with other spinor‐vector maps used in the literature.