Ariel Dobry

Magnetic susceptibility in the spin-Peierls system CuGeO3.

We study numerically, using a one-dimensional Heisenberg model coupled to the lattice in the adiabatic approximation, the spin-Peierls transition in the linear

Polarons in the three-band Peierls-Hubbard model: An exact diagonalization study

{\mathrm{Cu}}^{2+}

Spectral gap induced by structural corrugation in armchair graphene nanoribbons

spin-1/2 chains in the inorganic compound

Monte Carlo simulation of the role of defects as a melting mechanism

{\mathrm{CuGeO}}_{3}

Pressure dependence of the melting mechanism at the limit of overheating in Lennard-Jones crystals

, which has been recently observed experimentally. We suggest that the magnetic susceptibility, the temperature dependence of the spin gap, and the spin-Peierls transition temperature of this material can be reasonably described by including nearest and next-nearest-neighbor antiferromagnetic interactions along the chain. We estimate that the nearest-neighbor exchange parameter J is approximately 160 K, and that the next-nearest-neighbor exchange parameter is approximately 0.36J.

Role of atomic vacancies and boundary conditions on ballistic thermal transport in graphene nanoribbons

We have studied the three-band Peierls-Hubbard model describing the Cu-O layers in high-T

FROM SPINONS TO MAGNONS IN EXPLICIT AND SPONTANEOUSLY DIMERIZED ANTIFERROMAGNETIC CHAINS

_c

Theory of spin-Peierls transition beyond the adiabatic approximation

superconductors by using Lanczos diagonalization and assuming infinite mass for the ions. When the system is doped with one hole, and when the electron-lattice coupling is greater than a critical value, we found that the oxygens around one Cu contract and the hole self-traps forming a lattice and electronic small polaron. The self-trapped hole forms a local singlet analogous to the Zhang-Rice singlet in the undeformed lattice. We also studied the single-particle spectral function and the optical conductivity. We have found that the spectral weight, in general, is similar to that found in previous studies where the coupling with the lattice was absent. There is an anomalous transfer of spectral but, contrary to those studies, it goes to these localized polaronic states. However, this polaronic shift does not seem enough by itself to explain the pinning of the chemical potential observed in real materials. We compare our results to those obtained in inhomogeneous Hartree-Fock calculations and we discuss their relation with experiments.

Magnetic End States in a Strongly Interacting One-Dimensional Topological Kondo Insulator

AGNRs can be either metallic or semiconductor, depending on their width 8 . However, experiments suggest that AGNR are always insulators with a gap that scale with the inverse of its width 9 . The effect of the corrugation on the electronic properties of graphene has been studied in previous works by a tight binding type model 10 and by ab-initio LDA calculation 11 . The rippling induce a nonuniform gauge field whose effects has been analyzed by analogy with an applied magnetic field. In this sens a pseudo Landau levels (LL) were predicted. Regarding nanoribbons the effects of the rippling on the conductivity were analyzed in a model which include also the effect of the disorder produced by charged impurities 12 . Although this approach is quite realistic it can not isolate only the effect of the rippling in order to known the contribution of each perturbation separately. Therefore, in this work, our mainly purpose is to analyze the effect of the corrugation on the electronic structure and the transport properties of AGNRs. First, as a necessary previous step we study the electronic properties of corrugated graphene layers. We reanalyze the condition for the appearance of a flat band associated with the zero LL. We show that an strong rippling on the sheet is necessary to produce such a flat band. Then, we focus on the armchair border type nanoribbons. Particularly we analyze the case of the zero gap band-structure AGNRs. We show that due to rippling an spectral gap is open in otherwise conducting ribbons. We subsequent analyze the quantum conductance by the non equilibrium green’s function technique 13 (NEGF) and show that the opening of the gap manifest in a insulating behavior of the undoped samples.

Inhomogeneous superconducting phases in the frustrated Kondo-Heisenberg chain

We study in this paper the melting transition of a crystal of a fcc structure with the Lennard-Jones potential, by using isobaric-isothermal Monte Carlo simulations. Local and collective updates are sequentially used to optimize the convergence. We show the important role played by defects in the melting mechanism in favor of modern melting theories.