摘要:

The effect of impurity‐induced states on the long range order in a lamellar antiferromagnet (AF) is studied; and the magnetic phase‐diagram of lightly doped La2−xSrxCuO4is proposed. It is shown that long‐range magnetic perturbations and the layered structure cause the shrinkage of AF domains on the phase diagram and lead to the reentrant AF transition. A nonmonotonous dependence of the correlation length &xgr;2Don temperature T is obtained; the dependence &xgr;2D(x) is exponential for high T, and &xgr;2D∼x1/2for low T.

ISSN:0094-243X    

DOI:10.1063/1.39715

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Phonons in disordered dielectric materials at T=0 are always delocalized owing to the electric dipole interaction (no matter how weak it is). Real‐space renormalization of the dipole coupling is studied. A renormalization group equation for the distribution of dipole parameters is derived and its similarity with the Boltzmann kinetic equation is revealed. Conservation laws are found, the H‐theorem is proven. Stationary distributions from a six‐parameter manifold of fixed points. Energy transport is critical, slower than diffusive.

ISSN:0094-243X    

DOI:10.1063/1.39716

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A theory of the self‐trapping (ST) ratew(T), and also of the rate of the multi‐phonon trapping of charge carriers and excitons by defects is developed in the semiclassical approximation. The preexponential factor inw(T) is estimated in both low‐temperature (instanton) and high‐frequency (Arrhenius) limits.

ISSN:0094-243X    

DOI:10.1063/1.39718

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Dissipative dynamical systems with many degrees of freedom naturally evolve to a self‐organized critical state with fluctuations (avalanches) extending over all length‐ and time‐scales. The systems operate at the border of chaos, with zero Lyapunov exponent and algebraic growth of initial deviations. This picture has support from numerical and analytical model calculations, and from experiments by Held on sandpiles, by Babcock and Westervelt, and by Che and Suhl on magnetic domain patterns, and by God on earthquakes. Applications to turbulence, biology, and economics have been suggested.

ISSN:0094-243X    

DOI:10.1063/1.39719

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39720

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We summarize recent results concerning the stability of spatially‐coherent, time‐periodic states in noisy, classical, discrete‐time, many‐body systems with short‐range interactions. Generic stability of periodic k‐cycles with k≳2 can be achieved only by rules carefully constructed to exploit lattice anisotropy and so suppress droplet growth. For ordinary rules which do not utilize spatial anisotropy in this way, periodic k‐cycles with periods k≳2 are metastable rather than stable under generic conditions, losing spatial coherence through nucleation and growth of droplets.

ISSN:0094-243X    

DOI:10.1063/1.39721

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39722

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Three closely related types of excitonic quasiparticles have been recently studied: polaritons, phonoritons and photoritons. We show that the well known polariton displays frequency‐tunable intrinsic squeezing. Related to this is a new Quantum Optics Extinction Theorem. The phonoriton is associated with a ‘‘reconstruction’’ of the dispersion equation for the parent‐polariton: tests have so far proven elusive. Two new experiments are proposed and analyzed for identifying the phonoriton: Non‐Linear Resonance Brillouin Scattering, and Non‐Linear Reflectivity. Some remarks are made about the photoriton.

ISSN:0094-243X    

DOI:10.1063/1.39723

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39724

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In heterostructures with thick spacer layers the random potential in the channel created by remote impurity ions is smooth and can be treated classically, so that a percolation interpretation of the metal ‐ non‐metal transition (MNMT) is possible. The critical electron density,ncof the MNMT is found as a function of the spacer width and the ion density. The connection between the critical densityncfor the transition without magnetic field and the width of the plateaus of the integer quantum Hall effect (IQHE) in a sufficiently strong magnetic field is established. The width of the plateau as a function of spacer thickness and magnetic field is discussed.

ISSN:0094-243X    

DOI:10.1063/1.39725

出版商:AIP    

年代:1990

数据来源: AIP