470 research outputs found
Magnetic field induced transition in a wide parabolic well superimposed with superlattice
We study a parabolic quantum wells (PQW) with
square superlattice. The magnetotransport in PQW with
intentionally disordered short-period superlattice reveals a surprising
transition from electrons distribution over whole parabolic well to
independent-layer states with unequal density. The transition occurs in the
perpendicular magnetic field at Landau filling factor and is
signaled by the appearance of the strong and developing fractional quantum Hall
(FQH) states and by the enhanced slope of the Hall resistance. We attribute the
transition to the possible electron localization in the x-y plane inside the
lateral wells, and formation of the FQH states in the central well of the
superlattice, driven by electron-electron interaction.Comment: 5 pages, 4 figure
Interplay of the exciton and electron-hole plasma recombination on the photoluminescence dynamics in bulk GaAs
We present a systematic study of the exciton/electron-hole plasma
photoluminescence dynamics in bulk GaAs for various lattice temperatures and
excitation densities. The competition between the exciton and electron-hole
pair recombination dominates the onset of the luminescence. We show that the
metal-to-insulator transition, induced by temperature and/or excitation
density, can be directly monitored by the carrier dynamics and the
time-resolved spectral characteristics of the light emission. The dependence on
carrier density of the photoluminescence rise time is strongly modified around
a lattice temperature of 49 K, corresponding to the exciton binding energy (4.2
meV). In a similar way, the rise-time dependence on lattice temperature
undergoes a relatively abrupt change at an excitation density of 120-180x10^15
cm^-3, which is about five times greater than the calculated Mott density in
GaAs taking into account many body corrections.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
QSPR modeling aqueous solubility of polychlorinated biphenyls by optimization of correlation weights of local and global graph invariants
Aqueous solubilities of polychlorinated biphenyls have been correlated with topological molecular descriptors which are functions of local and global invariants of labeled hydrogen filled graphs. Morgan extended connectivity and nearest neighboring codes have been used as local graph invariants. The number of chlorine atoms in biphenyls has been employed as a global graph invariant. Present results show that taking into account correlation weights of global invariants gives quite reasonable improvement of statistical characteristics for the prediction of aqueous solubilities of polychlorinated biphenyls.Instituto de Investigaciones FisicoquÃmicas Teóricas y AplicadasFacultad de Ciencias Exacta
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