76 research outputs found
Photoemission spectra of : a theoretical analysis
Recent angle resolved photoemission (ARPES) results for the insulating
cuprate have provided the first experimental data
which can be directly compared to the (theoretically) well--studied problem of
a single hole propagating in an antiferromagnet. The ARPES results reported a
small bandwidth, providing evidence for the existence of strong correlations in
the cuprates. However, in the same experiment some discrepancies with the
familiar 2D model were also observed. Here we discuss a comparison
between the ARPES results and the quasiparticle dispersion of both (i) the
Hamiltonian and (ii) the three--band Hubbard model in the
strong--coupling limit. Both model Hamiltonians show that the experimentally
observed one--hole band structure can be approximately reproduced using
reasonable values for , or the direct oxygen hopping amplitude .Comment: 11 pages, RevTex version 3.0, 3 postscript figures, LaTeX file and
figures have been uuencoded
Quantum phase transition in the Frenkel-Kontorova chain: from pinned instanton glass to sliding phonon gas
We study analytically and numerically the one-dimensional quantum
Frenkel-Kontorova chain in the regime when the classical model is located in
the pinned phase characterized by the gaped phonon excitations and devil's
staircase. By extensive quantum Monte Carlo simulations we show that for the
effective Planck constant smaller than the critical value the
quantum chain is in the pinned instanton glass phase. In this phase the
elementary excitations have two branches: phonons, separated from zero energy
by a finite gap, and instantons which have an exponentially small excitation
energy. At the quantum phase transition takes place and for
the pinned instanton glass is transformed into the sliding
phonon gas with gapless phonon excitations. This transition is accompanied by
the divergence of the spatial correlation length and appearence of sliding
modes at .Comment: revtex 16 pages, 18 figure
Human Resource Flexibility as a Mediating Variable Between High Performance Work Systems and Performance
Much of the human resource management literature has demonstrated the impact of high performance
work systems (HPWS) on organizational performance. A new generation of studies is
emerging in this literature that recommends the inclusion of mediating variables between HPWS
and organizational performance. The increasing rate of dynamism in competitive environments
suggests that measures of employee adaptability should be included as a mechanism that may
explain the relevance of HPWS to firm competitiveness. On a sample of 226 Spanish firms, the
study’s results confirm that HPWS influences performance through its impact on the firm’s
human resource (HR) flexibility
Modeling the phase diagram of carbon
Contains fulltext :
32748.pdf (publisher's version ) (Open Access
Modeling the phase diagram of carbon
We determined the phase diagram involving diamond, graphite, and liquid carbon using a recently developed semiempirical potential. Using accurate free-energy calculations, we computed the solid-solid and solid-liquid phase boundaries for pressures and temperatures up to 400 GPa and 12 000 K, respectively. The graphite-diamond transition line that we computed is in good agreement with experimental data, confirming the accuracy of the employed empirical potential. On the basis of the computed slope of the graphite melting line, we rule out the hotly debated liquid-liquid phase transition of carbon. Our simulations allow us to give accurate estimates of the location of the diamond melting curve and of the graphite-diamond-liquid triple point
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