The Experts below are selected from a list of 2089794 Experts worldwide ranked by ideXlab platform
Alex Zunger - One of the best experts on this subject based on the ideXlab platform.
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Optical consequences of Long-Range Order in wurtzite Al x Ga 1 − x N alloys
Physical Review B, 2003Co-Authors: S. V. Dudiy, Alex ZungerAbstract:The effect of 1:1 long range Order on optical properties of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ alloys is investigated by means of first-principles calculations combined with large-scale atomistic empirical-pseudopotential simulations. We propose an intra-band mechanism of Ordering-induced band gap reduction for different optical polarization. The scaling of band gap reductions with Order parameter is analyzed. Our simulations of inhomogeneous Ordering suggest that coexistence of Ordered and random domains may explain the large magnitude of the observed redshifts upon Ordering.
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Dependence of Optical Properties of Semiconductor Alloys on Long Range Order, Strain and Pressure
MRS Online Proceedings Library, 1995Co-Authors: Su-huai Wei, Alberto Franceschetti, Alex ZungerAbstract:Many III–V semiconductor alloys exhibit spontaneous (111) alternate monolayer Ordering when grown from the vapor phase. We have studied theoretically the Ordering induced changes in the optical properties of the semiconductor alloys. We describe (i) the change of the band gap Δ E _ g and the valence band splitting Δ E _12 as functions of the long range Order parameter η, (ii) the consequence of coexistence of (001) epitaxial strain and (111) chemical Ordering on the optical properties, (iii) optical anisotropy and spin polarization effects in the Ordered alloy, (iv) theory of reflectance-difference spectroscopy in Ordered alloy, and (v) the Ordering-induced changes on high energy E _1 and E _2 transitions. Specific, experimentally testable predictions are listed in the summary section.
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Short- and Long-Range-Order effects on the electronic properties of III-V semiconductor alloys
Physical Review B, 1995Co-Authors: Kurt A. Mäder, Alex ZungerAbstract:This leads to an indirect-gap to direct-gap crossover in Al{sub 0.5}Ga{sub 0.5}As with sufficient clustering. (iii) The band-gap reduction is accompanied by a localization of band-edge wave functions on certain types of clusters. The clusters act as ``isoelectronic impurities`` which localize states if their concentration (i.e., the degree of short-range Order) is large enough. Electrons at the conduction-band minimum localize on the cations with lower {ital s}-orbital energies. The band-gap reduction and wave-function localization of alloys with short-range Order is compared to the effects of Long-Range Order, where the gap reduction is due to level repulsion between zone-folding conduction states. Numerical results are given for CuPt-type Long-Range Order of AlGaAs{sub 2}, GaInP{sub 2}, and AlInAs{sub 2}. For complete Ordering, the band-gap reduction relative to the random alloys are 0.36, 0.49, and 0.16 eV, respectively.
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Evolution of alloy properties with Long-Range Order.
Physical review letters, 1992Co-Authors: D. B. Laks, Su-huai Wei, Alex ZungerAbstract:We present a general theory of compounds with partial Long-Range Order. We derive a simple formula that determines the properties of a partially Ordered compound from those of the perfectly random alloy and the fully Ordered compound. The formula makes accurate predictions of both formulation energies and electronic band structures. We also use the formula to predict the band gaps of Al[sub 1[minus][ital x]]Ga[sub [ital x]]As/GaAs superlattices.
Ettore Vicari - One of the best experts on this subject based on the ideXlab platform.
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Quasi-Long-Range Order in trapped systems
Physical Review A, 2011Co-Authors: Federico Crecchi, Ettore VicariAbstract:We investigate the effects of a trapping space-dependent potential on the low-temperature quasi-Long-Range Order phase of two-dimensional particle systems with a relevant U(1) symmetry, such as quantum atomic gases. We characterize the universal features of the trap-size dependence using scaling arguments. The resulting scenario is supported by numerical Monte Carlo simulations of a classical two-dimensional XY model with a space-dependent hopping parameter, the inhomogeneity of which is analogous to that arising from the trapping potential in experiments of atomic gases.
Dietrich Belitz - One of the best experts on this subject based on the ideXlab platform.
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Long-Range Order versus random-singlet phases in quantum antiferromagnetic systems with quenched disOrder.
Physical Review Letters, 1996Co-Authors: T. R. Kirkpatrick, Dietrich BelitzAbstract:The stability of antiferromagnetic Long-Range Order against quenched disOrder is considered. A simple model of an antiferromagnet with a spatially varying Neel temperature is shown to possess a nontrivial fixed point corresponding to Long-Range Order that is stable unless either the Order parameter or the spatial dimensionality exceeds a critical value. The instability of this fixed point corresponds to the system entering a random-singlet phase. The stabilization of Long-Range Order is due to quantum fluctuations, whose role in determining the phase diagram is discussed.
Federico Crecchi - One of the best experts on this subject based on the ideXlab platform.
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Quasi-Long-Range Order in trapped systems
Physical Review A, 2011Co-Authors: Federico Crecchi, Ettore VicariAbstract:We investigate the effects of a trapping space-dependent potential on the low-temperature quasi-Long-Range Order phase of two-dimensional particle systems with a relevant U(1) symmetry, such as quantum atomic gases. We characterize the universal features of the trap-size dependence using scaling arguments. The resulting scenario is supported by numerical Monte Carlo simulations of a classical two-dimensional XY model with a space-dependent hopping parameter, the inhomogeneity of which is analogous to that arising from the trapping potential in experiments of atomic gases.
Bao-heng Zhao - One of the best experts on this subject based on the ideXlab platform.
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OFF-DIAGONAL Long-Range Order : MEISSNER EFFECT AND FLUX QUANTIZATION
Physical Review B, 1995Co-Authors: H. T. Nieh, Gang Su, Bao-heng ZhaoAbstract:There has been a proof by Sewell that the hypothesis of off-diagonal Long-Range Order in the reduced density matrix $\rho _2$ implies the Meissner effect. We present in this note an elementary and straightforward proof that not only the Meissner effect but also the property of magnetic flux quantization follows from the hypothesis. It is explicitly shown that the two phenomena are closely related, and phase coherence is the origin for both.
