Electron-Electron Interactions on the Edge States of Graphene: A Many Body Configuration Interaction Study

We have studied zigzag and armchair graphene nano ribbons (GNRs), described by the Hubbard Hamiltonian using quantum many body configuration interaction methods. Due to finite termination, we find that the bipartite nature of the graphene lattice gets destroyed at the edges making the ground state of the zigzag GNRs a high spin state, whereas the ground state of the armchair GNRs remains a singlet. Our calculations of charge and spin densities suggest that, although the electron density prefers to accumulate on the edges, instead of spin polarization, the up and down spins prefer to mix throughout the GNR lattice. While the many body charge gap results in insulating behavior for both kinds of GNRs, the conduction upon application of electric field is still possible through the edge channels because of their high electron density. Analysis of optical states suggest differences in quantum efficiency of luminescence for zigzag and armchair GNRs, which can be probed by simple experiments.Comment: 5 pages, 4 figure

Study of Apollo water impact. Volume 8 - Unsymmetric shells of revolution analysis Final report

Numerical analysis of static, and dynamic shell response to water impact load

Optical conductivity in the CuO double chains of PrBa_2Cu_4O_8: Consequences of charge fluctuation

We calculate the optical conductivity of the CuO double chains of PrBa$_2$Cu$_4$O$_8$ by the mean-field approximation for the coupled two-chain Hubbard model around quarter filling. We show that the $\sim$40 meV peak structure, spectral shape, and small Drude weight observed in experiment are reproduced well by the present calculation provided that the stripe-type charge ordering presents. We argue that the observed anomalous optical response may be due to the presence of stripe-type fluctuations of charge carriers in the CuO double chains; the fast time scale of the optical measurement should enable one to detect slowly fluctuating order parameters as virtually a long-range order.Comment: 7 pages, 5 eps figure

Phase Diagram of the tt--UU--V1V_1--V2V_2 Model at Quarter Filling

We examine the ground-state properties of the one-dimensional Hubbard model at quarter filling with Coulomb interactions between nearest-neighbors $V_1$ and next-nearest neighbors $V_2$. Using the density-matrix renormalization group and exact diagonalization methods, we obtain an accurate ground-state phase diagram in the $V_1$-$V_2$ plane with three different phases: $2k_{\rm F}$- and $4k_{\rm F}$-charge-density-wave and a broad metallic phase in-between. The metal is a Tomonaga-Luttinger-liquid whose critical exponent $K_{\rho}$ is largest around $V_1=2V_2$, where $V_1$ and $V_2$ are frustrated, and smallest, $K_{\rho}=0.25$, at the boundaries between the metallic phase and each of the two ordered phases.Comment: 4 pages, 5 figures, sumitted to PR

A Model Study of the Low-Energy Charge Dynamics of NaV_2O_5

An exact-diagonalization technique on small clusters is used to calculate the dynamical density correlation functions of the dimerized t-J chain and coupled anisotropic t-J ladders (trellis lattice) at quarter filling, i.e., the systems regarded as a network of pairs (dimers or rungs) of sites coupled weakly via the hopping and exchange interactions. We thereby demonstrate that the intersite Coulomb repulsions between the pairs induce a low-energy collective mode in the charge excitations of the systems where the internal charge degrees of freedom of the pairs play an essential role. Implications to the electronic states of NaV_2O_5, i.e., fluctuations of the valence state of V ions and phase transition as a charge ordering, are discussed.Comment: 4 pages, 4 gif figures. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to [email protected]

Vector Tactile Sensing by a Single Sensor Element of Vibratory Microcantilever Based on Multimode Resonant Frequency Shift

AbstractVibratory force sensors have been fabricated using piezoelectric capacitors on microcantilevers for triaxial sensitivity by a single sensor element. The cantilevers have been formed into three-dimensionally curved shape by controlling residual stress combination of the multilayered structure. Triaxial tactile sensitivity of the cantilever has been analyzed under a load application onto the surface of an elastomer in which the cantilever is embedded. The cantilever is converse-piezoelectrically excited by an external ac voltage and three resonant modes have been developed to detect the applied load vector components by individual sensor element. The applied load vectors are estimated by measured resonant frequencies of the single cantilever sensor in an error less than 1.1% to the full scale of the load 4kPa

Phase diagram of the one-dimensional Hubbard model with next-nearest-neighbor hopping

We study the one-dimensional Hubbard model with nearest-neighbor and next-nearest-neighbor hopping integrals by using the density-matrix renormalization group (DMRG) method and Hartree-Fock approximation. Based on the calculated results for the spin gap, total-spin quantum number, and Tomonaga-Luttinger-liquid parameter, we determine the ground-state phase diagram of the model in the entire filling and wide parameter region. We show that, in contrast to the weak-coupling regime where a spin-gapped liquid phase is predicted in the region with four Fermi points, the spin gap vanishes in a substantial region in the strong-coupling regime. It is remarkable that a large variety of phases, such as the paramagnetic metallic phase, spin-gapped liquid phase, singlet and triplet superconducting phases, and fully polarized ferromagnetic phase, appear in such a simple model in the strong-coupling regime.Comment: 11 pages, 8 figure