Surface ordering of MBE grown 001 gallium(05) aluminum(05) arsenic: A theoretical study

The surface kinetics of MBE growth of 001 {dollar}Ga\sb{x}Al\sb{1-x}As{dollar} is studied theoretically using the stochastic model which is based on the master equation approach and random distribution approximation. The kinetic processes included in the model are adsorption and surface migration. The surface ordering kinetics is studied as function of fluxes, flux ratio and substrate temperature. The growth parameters employed for the monatomic spices As are: fluxes 2{dollar}\sp\circ{dollar} A/sec, for cations with the cation to anion flux ratios 1: 10, and 1: 20. The growth parameter employ for the diatomic spices {dollar}As\sb2{dollar} are: fluxes 2{dollar}\sp\circ{dollar} A/sec. for cations with the cation to anion flux ratios 1: 10, 1: 20, and 1: 30, for cations to anions. The degree of ordering was obtained in terms of short range order (SRO), parameter. The surface ordering kinetics observed can be described in terms of effective surface migration rates of cations as follows. Lower temperature higher flux ratio results in smaller effective surface migration rates for cation. Beyond transition temperature the thermal energy, {dollar}\kappa\sb{B}T{dollar}, is large enough to break the Al-Ga bonds and causes thermal randomization of the Ga-Ga, Al-Al, and Ga-Al bonds. (Abstract shortened by UMI.)

Particle-hole character of the Higgs and Goldstone modes in strongly-interacting lattice bosons

We study the low-energy excitations of the Bose-Hubbard model in the strongly-interacting superfluid phase using a Gutzwiller approach and extract the single-particle and single-hole excitation amplitudes for each mode. We report emergent mode-dependent particle-hole symmetry on specific arc-shaped lines in the phase diagram connecting the well-known Lorentz-invariant limits of the Bose-Hubbard model. By tracking the in-phase particle-hole symmetric oscillations of the order parameter, we provide an answer to the long-standing question about the fate of the pure amplitude Higgs mode away from the integer-density critical point. Furthermore, we point out that out-of-phase oscillations are responsible for a full suppression of the condensate density oscillations of the gapless Goldstone mode. Possible detection protocols are also discussed.Comment: 6 pages, 3 figure

Competition between antiferromagnetism and superconductivity, electron-hole doping asymmetry and "Fermi Surface" topology in cuprates

We investigate the asymmetry between electron and hole doping in a 2D Mott insulator, and the resulting competition between antiferromagnetism (AF) and d-wave superconductivity (SC), using variational Monte Carlo for projected wave functions. We find that key features of the T = 0 phase diagram, such as critical doping for SC-AF coexistence and the maximum value of the SC order parameter, are determined by a single parameter which characterises the topology of the "Fermi surface" at half filling defined by the bare tight-binding parameters. Our results give insight into why AF wins for electron doping, while SC is dominant on the hole doped side. We also suggest using band structure engineering to control the parameter for enhancing SC.Comment: 4 pages, 4 figure