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231.
V.B. Timofeev A.V. Larionov J. Zeman G. Martinez V.I. Falko M. Bayer A. Forchel 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):39-43
Magnetooptical studies performed on a wide InGaAs/GaAs single quantum well indicate that optically non-active (dark) excitons
with total angular momentum play the role of a reservoir for the creation of free multiparticle excitonic complexes. After analyzing the magnetic field
evolution of the circularly polarized components of the low energy structure appearing in the main excitonic luminescence
line we assign this feature to the excitonic trion formation. The binding energy of the excitonic trions was estimated to
be of the order of 1 meV.
Received: 29 October 1997 / Received in final form: 20 February 1998 / Accepted: 21 February 1998 相似文献
232.
M. Dumm M. Dressel M. Nicklas P. Lunkenheimer A. Loidl M. Weiden F. Steglich B. Assmann H. Homborg P. Fulde 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):317-322
The magnetic susceptibility, using dc and electron spin resonance (ESR) methods, the specific heat, and the infrared properties
of the one-dimensional molecular semiconductors lithium phthalocyanine (LiPc) and the iodinated compound LiPcI have been investigated
for temperatures K. LiPc has a half-filled conduction band and is expected to be an organic metal. However, due to the strong Coulomb repulsion
the system is a one-dimensional Mott-Hubbard insulator with a Hubbard gap of 0.75 eV as inferred from optical measurements.
The localized electrons along the molecular stacks behave like a S = 1/2 antiferromagnetic spin chain. The spin susceptibility, as determined by ESR experiments, and the magnetic contribution
to the heat capacity show a Bonner-Fisher type of behavior with an exchange constant K. LiPcI is an intrinsic narrow-gap semiconductor with an optical gap of 0.43 eV. In ESR experiments it is silent, indicating
that all the unpaired electrons have been removed from the macrocycle via doping with iodine.
Received: 16 June 1998 / Accepted: 14 July 1998 相似文献
233.
The dynamics defined by the Hamiltonian
, where the
m are fixed random phases, is investigated for large values of A, and for
. For a given P
* and for
, this Hamiltonian is transformed through a rigorous perturbative treatment into a Hamiltonian where the sum of all the nonresonant terms, having a Q dependence of the kind cos(kQ – nt +
m) with
\Delta \upsilon$$
" align="middle" border="0">
, is a random variable whose r.m.s. with respect to the
m is exponentially small in the parameter
. Using this result, a rationale is provided showing that the statistical properties of the dynamics defined by H, and of the reduced dynamics including at each time t only the terms in H such that
, can be made arbitrarily close by increasing . For practical purposes close to 5 is enough, as confirmed numerically. The reduced dynamics being nondeterministic, it is thus analytically shown, without using the random-phase approximation, that the statistical properties of a chaotic Hamiltonian dynamics can be made arbitrarily close to that of a stochastic dynamics. An appropriate rescaling of momentum and time shows that the statistical properties of the dynamics defined by H can be considered as independent of A, on a finite time interval, for A large. The way these results could generalize to a wider class of Hamiltonians is indicated. 相似文献
234.
The association of complex formation with static quenching in CT systems was investigated. Evaluation of the data made evident
that the inner filter effect must be allowed for. Time-resolved and temperature-dependent stationary measurements of fluorescence
led to the separation of dynamic and static quenching components. The static quenching constant is discussed with respect
to the equilibrium constant of complex formation determined by absorption spectroscopy. 相似文献
235.
We present a series of rigorous examples of the Kondo lattice model that exhibit full ferromagnetism in the ground state.
The models are defined in one-, two- and three-dimensional lattices, and are characterized by a range of hopping terms, specific
electron filling, and large ferromagnetic coupling. Our examples show that a sufficient strong but finite exchange coupling
between conduction electrons and localized spins could overcome the competition from mobility of a finite density of electrons
and drive the system from a paramagnetic phase to a ferromagnetic phase. We also establish a relation of ferromagnetism between
the Hubbard model and Kondo lattice model. Meanwhile some rigorous results on ferromagnetism in the corresponding Hubbard
model are presented.
Received: 10 September 1997 / Revised: 15 October 1997 / Accepted: 17 October 1997 相似文献
236.
Y. J. Wang H. A. Nickel B. D. McCombe F. M. Peeters J. M. Shi G. Q. Hai X. -G. Wu T. J. Eustis W. Schaff 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
A detailed experimental study of electron cyclotron resonance (CR) has been carried out at 4.2 K in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well samples in fields up to 30 T. A strong avoided-level-crossing splitting of the CR energies due to resonant magnetopolaron effects is observed for all samples near the GaAs reststrahlen region. Resonant splittings in the region of AlAs-like interface phonon modes of the barriers are observed in two samples with narrower well width and smaller doping concentration. The interaction between electrons and the AlAs interface optical phonon modes has been calculated for our specific sample structures in the framework of the memory-function formalism. The calculated results are in good agreement with the experimental results, which confirms our assignment of the observed splitting near the AlAs-like phonon region is due to the resonant magnetopolaron interaction of electrons in the wells with AlAs-like interface phonons. 相似文献
237.
用玻色子组态混合和玻色子表面δ相互作用研究核谱 总被引:2,自引:0,他引:2
用玻色子组态混合波函数和玻色子表面δ相互作用研究了三玻色子核46Ti和54Cr的sdgIBMI的能谱和E2跃迁概率,理论计算结果令人满意,比sdIBMI能拟合出更多的能级和E2跃迁概率,而且它们的误差更小. 说明g玻色子在振动区也起着重要的作用,同时进一步证明了这种玻色子组态混合模型是成功的. 相似文献
238.
A theoretical investigation is carried out for an intermediate regime of optoacoustic interaction, close to the Bragg one,
by ultasonic Rayleigh surface waves in gyrotropic planar waveguides in an external electric field. A system of equations of
associated waves is presented which describes the planar optoacoustic interaction in intermediate, Raman—Nath, and Bragg regimes
of diffraction by ultrasonic surface waves in gyrotropic crystals with electrically induced anisotropy. It is shown that the
intermediate (transition) regime of optoacoustic interaction, which is characterized by an angular selectivity and by the
presence of several diffraction maxima, is the basic regime of diffraction. In this case diffracted light is generally elliptically
polarized with an ellipticity and polarization azimuth that depend on the external electric field intensity.
Translated from Zhurrnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 30–35, January–February, 1999. 相似文献
239.
V. V. Sobolev 《Journal of Applied Spectroscopy》1999,66(3):319-335
The article surveys the main unsolved problems of the electronic structure of nonmetals in a wide energy region of fundamental
absorption.
Udmurtia State University, 71, Krasnogeroiskaya Str., Izhevsk, 426034, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 66, No. 3, pp. 299–315, May–June, 1999. 相似文献
240.
The specific heat of Fermi–Pasta–Ulam systems has until now been estimated through the energy fluctuations of a suitable subsystem, and opposite answers were apparently provided concerning its possible vanishing for vanishing temperatures. In the present paper a more realistic numerical implementation of the specific heat measurement is discussed, which mimics the interaction of the FPU system with a calorimeter. It is found that there exists a freezing critical temperature below which the relaxation times to equilibrium between FPU system and calorimeter become relevant, so that the system presents aging and hysteresis features very similar to those familiar in glasses and spin glasses. In particular, in the framework of such a point of view involving finite long times, the specific heat appears to vanish for vanishing temperatures. 相似文献