Comparison of atomistic simulations and statistical theories for variable degree of long-range order in semiconductor alloys

2009 ◽  
Vol 80 (4) ◽  
Author(s):  
Yong Zhang ◽  
A. Mascarenhas ◽  
Su-Huai Wei ◽  
L.-W. Wang
Keyword(s):  
Long Range ◽  
Range Order ◽  
Atomistic Simulations ◽  
Variable Degree ◽  
Long Range Order ◽  
Semiconductor Alloys

Dependence of the optical properties of semiconductor alloys on the degree of long‐range order

1993 ◽  
Vol 62 (16) ◽  
pp. 1937-1939 ◽  
Author(s):  
Su‐Huai Wei ◽  
David B. Laks ◽  
Alex Zunger
Keyword(s):  
Optical Properties ◽  
Long Range ◽  
Range Order ◽  
Long Range Order ◽  
Semiconductor Alloys

The long‐range‐order structures of III‐V semiconductor alloys

1993 ◽  
Vol 73 (9) ◽  
pp. 4260-4265 ◽  
Author(s):  
Jun Ni ◽  
Xinchun Lai ◽  
Binglin Gu
Keyword(s):  
Long Range ◽  
Range Order ◽  
Long Range Order ◽  
Semiconductor Alloys ◽  
Order Structures

Dependence of Optical Properties of Semiconductor Alloys on Long Range Order, Strain and Pressure

1995 ◽  
Vol 417 ◽  
Author(s):  
Su-Huai Wei ◽  
Alberto Franceschetti ◽  
Alex Zunger
Keyword(s):  
Optical Properties ◽  
Long Range ◽  
High Energy ◽  
Range Order ◽  
Long Range Order ◽  
Semiconductor Alloys ◽  
Chemical Ordering ◽  
Epitaxial Strain ◽  
Reflectance Difference Spectroscopy ◽  
Induced Changes

AbstractMany 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 ΔE9, and the valence band splitting ΔE12 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 E1 and E2 transitions. Specific, experimentally testable predictions are listed in the summary section.

Superfluidity and Superconductivity

2018 ◽  
Author(s):  
Norman J. Morgenstern Horing
Keyword(s):  
Magnetic Field ◽  
Wave Function ◽  
Wave Packet ◽  
Long Range ◽  
Cooper Pair ◽  
Bose Condensation ◽  
Range Order ◽  
Condensed State ◽  
Long Range Order ◽  
Coherent Wave

Chapter 13 addresses Bose condensation in superfluids (and superconductors), which involves the field operator ψ‎ having a c-number component (<ψ(x,t)>≠0), challenging number conservation. The nonlinear Gross-Pitaevskii equation is derived for this condensate wave function<ψ>=ψ−ψ˜, facilitating identification of the coherence length and the core region of vortex motion. The noncondensate Green’s function G˜1(1,1′)=−i<(ψ˜(1)ψ˜+(1′))+> and the nonvanishing anomalous correlation function F˜∗(2,1′)=−i<(ψ˜+(2)ψ˜+(1′))+> describe the dynamics and elementary excitations of the non-condensate states and are discussed in conjunction with Landau’s criterion for viscosity. Associated concepts of off-diagonal long-range order and the interpretation of <ψ> as a superfluid order parameter are also introduced. Anderson’s Bose-condensed state, as a phase-coherent wave packet superposition of number states, resolves issues of number conservation. Superconductivity involves bound Cooper pairs of electrons capable of Bose condensation and superfluid behavior. Correspondingly, the two-particle Green’s function has a term involving a product of anomalous bound-Cooper-pair condensate wave functions of the type F(1,2)=−i<(ψ(1)ψ(2))+>≠0, such that G2(1,2;1′,2′)=F(1,2)F+(1′,2′)+G˜2(1,2;1′,2′). Here, G˜2 describes the dynamics/excitations of the non-superfluid-condensate states, while nonvanishing F,F+ represent a phase-coherent wave packet superposition of Cooper-pair number states and off-diagonal long range order. Employing this form of G2 in the G1-equation couples the condensed state with the non-condensate excitations. Taken jointly with the dynamical equation for F(1,2), this leads to the Gorkov equations, encompassing the Bardeen–Cooper–Schrieffer (BCS) energy gap, critical temperature, and Bogoliubov-de Gennes eigenfunction Bogoliubons. Superconductor thermodynamics and critical magnetic field are discussed. For a weak magnetic field, the Gorkov-equations lead to Ginzburg–Landau theory and a nonlinear Schrödinger-like equation for the pair wave function and the associated supercurrent, along with identification of the Cooper pair density. Furthermore, Chapter 13 addresses the apparent lack of gauge invariance of London theory with an elegant variational analysis involving re-gauging the potentials, yielding a manifestly gauge invariant generalization of the London equation. Consistency with the equation of continuity implies the existence of Anderson’s acoustic normal mode, which is supplanted by the plasmon for Coulomb interaction. Type II superconductors and the penetration (and interaction) of quantized magnetic flux lines are also discussed. Finally, Chapter 13 addresses Josephson tunneling between superconductors.

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