Quasiparticle Dynamics in the Kondo Lattice Model at Half Filling

We study spectral properties of quasiparticles in the Kondo lattice model in one and two dimensions including the coherent quasiparticle dispersions, their spectral weights and the full two-quasiparticle spectrum using a cluster expansion scheme. We investigate the evolution of the quasiparticle band as antiferromagnetic correlations are enhanced towards the RKKY limit of the model. In both the 1D and the 2D model we find that a repulsive interaction between quasiparticles results in a distinct antibound state above the two-quasiparticle continuum. The repulsive interaction is correlated with the emerging antiferromagnetic correlations and can therefore be associated with spin fluctuations. On the square lattice, the antibound state has an extended s-wave symmetry.Comment: 8 pages, 11 figure

Phenomenological theory of the s-wave state in superconductors without an inversion center

Abstract.: In materials without an inversion center of symmetry the spin degeneracy of the conducting band is lifted by an antisymmetric spin orbit coupling (ASOC). Under such circumstances, spin and parity cannot be separately used to classify the Cooper pairing states. Consequently, the superconducting order parameter is generally a mixture of spin singlet and triplet pairing states. In this paper we investigate the structure of the order parameter and its response to disorder for the most symmetric pairing state (A1). Using the example of the heavy Fermion superconductor CePt3Si, we determine characteristic properties of the superconducting instability. Depending on the type of the pairing interaction, the gap function is characterized by the presence of line nodes. We show that this line nodes move in general upon temperature. Such nodes would be essential to explain recent low-temperature data of thermodynamic quantities such as the NMR-T1 -1, London penetration depth, and heat conductance. Moreover, we study the effect of (non-magnetic) impurity on the superconducting stat

Anomalous Metal-Insulator Transition in Filled Skutterudite CeOs4_4Sb12_{12}

Anomalous metal-insulator transition observed in filled skutterudite CeOs$_4$Sb$_{12}$ is investigated by constructing the effective tight-binding model with the Coulomb repulsion between f electrons. By using the mean field approximation, magnetic susceptibilities are calculated and the phase diagram is obtained. When the band structure has a semimetallic character with small electron and hole pockets at $\Gamma$ and H points, a spin density wave transition with the ordering vector $\mathbf{Q}=(1,0,0)$ occurs due to the nesting property of the Fermi surfaces. Magnetic field enhances this phase in accord with the experiments.Comment: 4 pages, 4 figure

Field-induced phase transitions in a Kondo insulator

We study the magnetic-field effect on a Kondo insulator by exploiting the periodic Anderson model with the Zeeman term. The analysis using dynamical mean field theory combined with quantum Monte Carlo simulations determines the detailed phase diagram at finite temperatures. At low temperatures, the magnetic field drives the Kondo insulator to a transverse antiferromagnetic phase, which further enters a polarized metallic phase at higher fields. The antiferromagnetic transition temperature $T_c$ takes a maximum when the Zeeman energy is nearly equal to the quasi-particle gap. In the paramagnetic phase above $T_c$, we find that the electron mass gets largest around the field where the quasi-particle gap is closed. It is also shown that the induced moment of conduction electrons changes its direction from antiparallel to parallel to the field.Comment: 7 pages, 6 figure

Mean Field study of the heavy fermion metamagnetic transition

We investigate the evolution of the heavy fermion ground state under application of a strong external magnetic field. We present a richer version of the usual hybridization mean field theory that allows for hybridization in both the singlet and triplet channels and incorporates a self-consistent Weiss field. We show that for a magnetic field strength B*, a filling-dependent fraction of the zero-field hybridization gap, the spin up quasiparticle band becomes fully polarized--an event marked by a sudden jump in the magnetic susceptibility. The system exhibits a kind of quantum rigidity in which the susceptibility (and several other physical observables) are insensitive to further increases in field strength. This behavior ends abruptly with the collapse of the hybridization order parameter in a first-order transition to the normal metallic state. We argue that the feature at B* corresponds to the "metamagnetic transition" in YbRh2Si2. Our results are in good agreement with recent experimental measurements.Comment: 9+ pages, 5 figures. Final versio

Origin of Low-Energy Excitations in Charge-Ordered Manganites

The low-energy excitations in the charge-ordered phase of polycrystalline La0.25Ca0.75MnO3 are explored by frequency-domain terahertz spectroscopy. In the frequency range from 4 cm^-1 to 700 cm^-1 (energies 0.4 meV to 90 meV) and at temperatures down to 5 K, we do not detect any feature that can be associated with the collective response of the spatially modulated charge continuum. In the antiferromagnetically ordered phase, broad absorption bands appear in the conductivity and permittivity spectra around 30 cm^-1 and 100 cm^-1 which are assigned to former acoustic phonons optically activated due to a fourfold superstructure in the crystal lattice. Our results indicate that characteristic energies of collective excitations of the charge-ordered phase in La0:25Ca0:75MnO3, if any, lie below 1 meV. At our lowest frequencies of only few wavenumbers a strong relaxation is observed above 100 K connected to the formation of the charge-ordered state.Comment: 5 pages, 3 figure

Física y evolución del láser en odontología

El objetivo de este trabajo consiste en poder trasmitir al profesional odontólogo basado en una recopilación bibliográfica sobre la historia y orígenes físicos del láser junto a su evolución por lo cual se desarrolla los estudios de Newton sobre la luz e incorporando estos principios a las teorías postuladas por Bohr sobre emisión espontánea, y perfeccionando posteriormente estas teorías con los estudios de A. Einstein con su trabajo de emisión estimulada generando así las raíces para la obtención del láser y dándole a T. Maiman las herramientas para dar como resultado la creación del primer láser de rubí. El resultado de este trabajo será dar al odontólogo las herramientas para poder discernir el funcionamiento del láser comparando esta fuente de energía con la luz natural o artificialResumen publicado en Libro de resúmenes. Producción en Investigación, Docencia, Gestión, Extensión. Universidad Nacional de Rosario: Rosario, 2009.Facultad de Odontologí

Física y evolución del láser en odontología

El objetivo de este trabajo consiste en poder trasmitir al profesional odontólogo basado en una recopilación bibliográfica sobre la historia y orígenes físicos del láser junto a su evolución por lo cual se desarrolla los estudios de Newton sobre la luz e incorporando estos principios a las teorías postuladas por Bohr sobre emisión espontánea, y perfeccionando posteriormente estas teorías con los estudios de A. Einstein con su trabajo de emisión estimulada generando así las raíces para la obtención del láser y dándole a T. Maiman las herramientas para dar como resultado la creación del primer láser de rubí. El resultado de este trabajo será dar al odontólogo las herramientas para poder discernir el funcionamiento del láser comparando esta fuente de energía con la luz natural o artificialResumen publicado en Libro de resúmenes. Producción en Investigación, Docencia, Gestión, Extensión. Universidad Nacional de Rosario: Rosario, 2009.Facultad de Odontologí