Quantum Theory of Advanced Materials

Both the size and the magnetic-field dependences of low-lying spectra of two-dimensional (2D) graphene based magnetic dot and ring in perpendicular inhomogeneous magnetic fields, where the magnetic field is zero inside the dot and ring, and constant elsewhere, are studied by the massless Dirac-Weyl equation. Numerical results obtained from direct diagonalization with 2D harmonic basis show that, under nonuniform magnetic fields, the higher Landau levels (N >= 1) for such massless Dirac electron interacting system in general become nondegenerate and split into discrete angular momentum states with level crossings with the lowest one (N=0) being an exception. (C) 2010 American Institute of Physics. [doi:10.1063/1.3435478]

Using classical mechanical and quantum Monte Carlo methods we trace the ground-state behavior with an applied magnetic field of localized electron pair states in a quantum dot. By developing a method to treat nonconserved paramagnetic interactions using variational and diffusion quantum Monte Carlo techniques we find (i) a single-triplet transition at very small magnetic field strengths, (ii) enhanced localization of the two electrons with increasing magnetic field, and (iii) a mechanism for pair breakup that is different from that proposed recently by Wan et al. [Phys. Rev. Lett. 75, 2879 (1995)]. [S0163-1829(98)04016-8].

The low-lying energy spectra of bilayer graphene in a perpendicular magnetic field B(r)(z) over cap were obtained by numerical diagonalization of the Hamiltonian. We assumed that B(r) takes on the shape of a circular dot or a ring. Under such a nonuniform field, the lowest-energy Landau levels, with N- = 0,1, remain invariant with a zero eigenvalue. For other Landau levels, complicated level-splitting and level-crossings take place when the effective radius of the dot or ring increases. (C) 2012 Elsevier Ltd. All rights reserved.

In this paper, we study the low-lying energy spectra of a two-dimensional (2D) graphene-based magnetic dot in a perpendicular and radially inhomogeneous magnetic field with the use of the massless Dirac-Weyl equation. Numerical calculations are performed using 2D harmonic basis states for direct diagonalization. Effects of both the dot size and the magnetic field on the low-lying energy spectra are discussed.

We have studied the structural stability of thin silver films with thicknesses of N = 1 to 15 monolayers, deposited on an Fe(100) substrate. Photoemission spectroscopy results show that films of N = 1, 2, and 5 monolayer thicknesses are structurally stable for temperatures above 800 kelvin, whereas films of other thicknesses are unstable and bifurcate into a film with N +/- 1 monolayer thicknesses at temperatures around 400 kelvin, The results are in agreement with theoretical predictions that consider the electronic energy of the quantum well associated with a particular film thickness as a significant contribution-to the film stability.