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1.
We consider the 2D quenched–disordered q–state Potts ferromagnets and show that in the translation invariant measure, averaged over the disorder, at self–dual points any amalgamation of q?1 species will fail to percolate despite an overall (high) density of 1?q ?1. Further, in the dilute bond version of these systems, if the system is just above threshold, then throughout the low temperature phase there is percolation of a single species despite a correspondingly small density. Finally, we demonstrate both phenomena in a single model by considering a “perturbation” of the dilute model that has a self–dual point. We also demonstrate that these phenomena occur, by a similar mechanism, in a simple coloring model invented by O. Häggström. 相似文献
2.
Zhao-Xian Yu Zhi-Yong Jiao Fu-ping Liu 《International Journal of Theoretical Physics》2008,47(6):1625-1629
By using of the invariant theory, we have studied the phase of exciton emission in a semiconductor microcavity, the dynamical
and geometric phases are presented respectively. The Aharonov-Anandan phase is also obtained in the case of cyclical evolution. 相似文献
3.
A. Amo D. Ballarini D. Sanvitto E. Kozhemyakina L. Via M.S. Skolnick J.S. Roberts 《Superlattices and Microstructures》2008,43(5-6):449
We present a time resolved experiment in which we dynamically tailor the occupation and temperature of a photogenerated exciton distribution in QWs by excitation with two delayed picosecond pulses. The modification of the excitonic distribution results in ultrafast changes in the PL dynamics. Our experimental results are well accounted by a quasiequilibrium thermodynamical model, which includes the occupation and momentum distribution of the excitons. We use this model and the two-pulse experimental technique to study the polariton dynamics in InGaAs-based microcavities in the strong coupling regime. In particular, we demonstrate that resonantly injected upper polaritons mainly relax to the lower polariton branch via scattering to large momentum polariton states, producing the warming of the polariton reservoir. 相似文献
4.
The optical refractive index changes and absorption coefficients of quantum wells (QWs) are theoretically investigated with considering exciton effects within the framework of the fractional-dimensional space approach. The exciton wave functions and bound energies are obtained as a function of spatial dimensionality, and the dimension increases with the well width increasing. Then optical properties are obtained by using the compact-density matrix approach and an iterative method. Numerical results are presented for wurtzite ZnO/MgxZn1−xO QWs. The calculated results show that the changes of refractive index and absorption coefficients are greatly enhanced due to the quantum confinement of exciton. And the smaller the QW width (dimension) is, the larger influence of exciton on the optical properties will be. Furthermore, the exciton effects make the resonant peaks move to a lower energy. In addition, the optical properties are related to the QW width, the incident optical intensity and carrier density. 相似文献
5.
Phase transitions of the anti-fluorite compounds Mg2Ge and Mg2Sn under high pressure were investigated using the first-principles plane-wave method within the pseudopotential and generalized gradient approximations. The calculated results show that Mg2Ge and Mg2Sn undergo two first-order phase transitions at high pressure and the sequence of the pressure-induced phase transitions is from the anti-fluorite to the anti-cotunnite, and then to the Ni2In-type structure. The high pressure behaviors of Mg2Ge and Mg2Sn are similar to Mg2Si and the isostructural alkali-metal oxide Li2O. Moreover, the electronic and optical properties of both the anti-fluorite and the high-pressure phases are presented. 相似文献
6.
We study the phase separation dynamics in finite lifetime systems. Particles created by the external fields are unstable and decay within the finite lifetime. Effects of the particle lifetime and the interparticle interaction for the phase separation dynamics are discussed. In our theory, the formulation is based on the coarse-grained lattice gas model. As a result, effects of the finite lifetime are that the phase separation is restrained and that the finite size of domains remain finally at t = X . 相似文献
7.
《Current Applied Physics》2014,14(9):1325-1330
The exciton eigenstates and biexciton interaction energies in a spherical core–shell hetero-nano structure in the type II and the quasi-type II carrier localization regimes have been analyzed. For the analysis, we have evaluated the electron–hole overlap integral, the binding energy of exciton ground state, and the interaction energy of bi-exciton ground state in the structure. In the evaluation, the first order perturbation approach has been employed, where the direct Coulomb interaction energy, the surface polarization energy and the dielectric solvation energy are included. Our results show that the exciton eigenenergies and exciton–exciton interaction energy strongly depend on the choice of materials on which both the dielectric constants and the electron and hole effective masses rely. 相似文献
8.
9.
High pressure can effectively control the phase transition of MoTe2 in experiment, but the mechanism is still unclear. In this work, we show by first-principles calculations that the phase transition is suppressed and phase becomes more stable under high pressure, which originates from the pressure-induced change of the interlayer band occupancies near the Fermi energy. Specifically, the interlayer states of phase tend to be fully occupied under high pressure, while they keep partially occupied for the phase. The increase of the band occupancies makes the phase more favorable in energy and prevents the structure changing from to phase. Moreover, we also analyze the superconductivity under high pressure based on BCS theory by calculating the density of states and phonon spectra. Our results may shed some light on understanding the relationship between the interlayer band occupancy and crystal stability of MoTe2 under high pressures. 相似文献
10.
Shudong Wu 《Physica B: Condensed Matter》2011,406(24):4634-4638
The effects of transverse electric field on the energy levels of electron and heavy hole, exciton binding energy and excitonic absorption spectra of GaAs parabolic quantum wire are theoretically investigated in detail. The results indicate that the electron and hole energy levels, exciton binding energy, excitonic absorption coefficient and absorption energy becomes smaller with the increase of electric field. That is more significant at the condition of weaker parabolic confinement potential. The phenomena can be explained by the separation of overlap integral of the electron and hole at the ground states. 相似文献
11.
Within the framework of the effective-mass approximation, the exciton states and interband optical transitions in InxGa1−xN/GaN strained quantum dot (QD) nanowire heterostructures are investigated using a variational method, in which the important built-in electric field (BEF) effects, dielectric-constant mismatch and three-dimensional confinement of the electron and hole in InxGa1−xN QDs are considered. We find that the strong BEF gives rise to an obvious reduction of the effective band gap of QDs and leads to a remarkable electron-hole spatial separation. The BEF, QD height and radius, and dielectric mismatch effects have a significant influence on exciton binding energy, electron interband optical transitions, and the exciton oscillator strength. 相似文献
12.
Time-resolved magneto photoluminescence in a diluted magnetic semiconductor Cd 0.9 Mn 0.1 Te has been carried out with varying exciton density from 10 14 to 10 19 cm m 3 . The reduction of the Zeeman shift and that of the magnetic polaron energy was found under strong photoexcitation. The spectral feature is interpreted in terms of the heating of the manganese spin subsystem. Polarization dependence of the spin heating is observed for the first time, revealing the contribution of the spin flip between excitons and magnetic ions to the heating process. 相似文献
13.
We report about recent X-ray absorption spectroscopy (XAS) measurements on solid and liquid AgI under high pressure. The structural behaviour of AgI has been investigated to pressures P~4.3 GPa at room temperature and to P~1.8 GPa at 1100 K. The high temperature/high pressure conditions have been obtained by means of a large-volume press of the Paris-Edinburgh type, coupled with a 10 mm boron/epoxy biconical gasket. The absorption spectra have been collected in transmission mode, both at the K-edge of Ag and I, and the samples have been characterized in situ by energy scanning X-ray diffraction at fixed angles. Our XAS results for solid AgI are compatible with previous X-ray diffraction measurements. For liquid AgI, we observe a slight change in the intensity and a shift in the frequency of the XAS oscillations with respect to what obtained in the case of the ambient pressure liquid. 相似文献
14.
N.A. Tahir A. Shutov I.V. Lomonosov A.R. Piriz R. Redmer T. Stöhlker H. Geissel C. Deutsch V.E. Fortov 《等离子体物理论文集》2011,51(4):309-321
The forthcoming F acility for A ntiprotons and I on R esearch (FAIR) at Darmstadt, is going to be a unique accelerator facility that will deliver high quality, strongly bunched, well focused, intense beams of heavy ions that will lead to unprecedented specific power deposition in solid matter. This will generate macroscopic samples of H igh E nergy D ensity (HED) matter with fairly uniform physical conditions. These samples can be used to study the thermophysical and transport properties of HED matter. Extensive theoretical work has been carried out over the past decade to design numerous dedicated experiments to study HED physics at the FAIR, which has provided the basis for the HEDgeHOB ( H igh E nergy D ensity Matter Ge nerated by H eavy I o n B eams) scientific proposal. This work is still in progress as the feasibility studies for more experimental schemes are being carried out. Another, very important research area that will benefit tremendously from the FAIR facility, is the production of radioactive beams. A superconducting fragment separator, Super–FRS is being designed for the production and separation of rare radioactive isotopes. Unlike the HED targets, the Super–FRS production target should not be destroyed or damaged by the beam, but should remain intact during the long experimental campaign. However, the high level of specific power deposited in the production target by the high intensity ion beam at FAIR, could cause serious problems to the target survival. These HED issues related to the Super–FRS production target are also discussed in the present paper (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
15.
Qi-Jun Liu Zheng-Tang LiuQian-Qian Gao Li-Ping FengHao Tian Feng YanWei Zeng 《Physics letters. A》2011,375(14):1608-1611
We report a direct computational result of a phase transformation from the 3R phase to the 2H phase in CuAlO2 with the application of tensile stress using the first-principles density functional theory calculations. The calculations of enthalpy variation with tensile stress indicates the 3R-to-2H phase transformation is expected to occur around −26.0 GPa. As the applied tensile stress increases, the independent elastic constants of 3R- and 2H-CuAlO2 show the presences of mechanical instability at −27.5 and −27.6 GPa, which are possibly related with the ideal tensile strength. 相似文献
16.
We investigate the adiabatic and dynamical natures of the lattice relaxation of excitons in strongly coupled electron-phonon (e-ph) systems using the extended Peierls-Hubbard model, so as to clarify the possible mechanisms of the photoinduced structural phase transition (PISPT) via multi-photon. Focusing on the growth process of relaxed domains that is induced by multi-photoexcitation, we calculate the adiabatic potential energy surfaces relevant to the nonlinear lattice relaxations of excitons in this process. Calculated potentials lead to an essential model of a multi-stepwise potential-crossing (MSPC) system that is composed of many displaced harmonic oscillators as an elementary process of the domain growth in the strongly coupled e-ph systems. We also investigate the dynamical natures in such MSPC systems calculating the time-developments the excited wave packet in this system using the density operator. It is concluded from calculated results that the system possibly develops from the lowest-energy potential state to the higher ones by the effect of the photoexcitations followed by the lattice relaxations. 相似文献
17.
Considering the strong built-in electric field (BEF), dielectric-constant mismatch and 3D confinement of the electron and hole, the exciton states and interband optical transitions in [0 0 0 1]-oriented Ga-rich wurtzite InxGa1−xN/GaN strained quantum dot (QD) nanowire heterostructures are investigated theoretically using a variational approach under the effective mass approximation. We find that the strong BEF gives rise to an obvious reduction of the effective band gap of QDs and leads to a remarkable electron-hole spatial separation. The BEF, QD height and radius, and dielectric mismatch effects have a significant influence on exciton binding energy, electron interband optical transitions, and the radiative decay time. Our calculations show that the radiative decay time of the redshifted transitions is large and increases almost exponentially when the QD height increases, which is in good agreement with the previous experimental and theoretical results. 相似文献
18.
Igor Luka?evi? 《Physica B: Condensed Matter》2011,406(18):3410-3416
Using density functional theory and density functional perturbation theory we have studied the effects of hydrostatic pressure on lattice dynamics, dielectric and thermodynamic properties of the rocksalt (NaCl) and CsCl phases of SrO. The stability of the NiAs type structure, experimentally confirmed to be stable in BaO, is also investigated. Studying the lattice dynamics of the NaCl and CsCl phases at various pressures, in the range of the phase stability, we have found the lattice dynamical instabilities which govern the phase transitions between NaCl and CsCl phases with increasing and decreasing pressure. By monitoring the behaviour of the found soft modes, we have calculated the transition pressures upon compression and decompression of SrO crystal. Lattice dynamics calculations reveal that the rocksalt and CsCl structures are unstable with respect to the soft transversal acoustic modes at single points of the Brillouin zone, which points to the fact that the transitions are of displacive type. Responses to electric fields and thermodynamic properties at high pressures are also given and discussed. All our results are in a good agreement with experimental data where applicable. 相似文献
19.
In this paper we describe the results of an energy dispersive X-ray diffraction experiment carried out in the ZnSe 1 m x Te x alloy and pure ZnSe under high pressure. In the downstroke the cinnabar phase is observed between the rocksalt and the zincblende phases. The analysis of the whole series of compositions ( x =0, 0.05, 0.1 and 0.2) enables us to establish its lattice parameters in ZnSe ( a =3.785 + and c =8.844 + at 10.5 GPa). The X-ray diffraction pattern simulation suggests that the internal parameters u and v are close to 0.5, indicating that the cinnabar phase in ZnSe is similar to that observed in GaAs and ZnTe. The cinnabar's stability range decreases as the Te content is reduced. 相似文献
20.
金属钨三键多核金属有机配合物高压拉曼及红外光谱研究 总被引:2,自引:0,他引:2
许振华 《光谱学与光谱分析》2001,21(5):596-598
研究了金属钨三键多核金属有机配合物 [Cl(CO) 2 (DPPE)WCC6 H4CCC6 H4NC]2 ReCl(CO) 3(DPPE =bis(diphenylphosphino)ethane,(Ph) 2 PCH2 CH2 P(Ph) 2 )不同压力下的拉曼和红外光谱 (最高压力约 5 0kbar)。配合物在 3 0kbar存在一压力诱导二级相变。金属钨三键伸缩振动ν(WC)压力相关 (dν/dp)在低压相区 ( 0 5 9cm-1·(kbar) -1)与高压相区 ( 0 0 4cm-1·(kbar) -1)差别很大 (约 15倍 )。在高压下 ,从基团Cl(CO) 2 (DPPE)WC中的金属钨W向COπ 轨道的π 反馈明显增强 ,WC的键强度减弱 ,力常数减小和ν(WC)降低 ;此效应与压力缩短WC键 ,增大力常数和增加ν(WC)的效应互相竞争。 相似文献