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991.
We study quantum antiferromagnetism on the highly frustrated planar pyrochlore lattice, also known as the square lattice with crossings. The quantum Heisenberg antiferromagnet on this lattice is of interest as a two-dimensional analogue of the pyrochlore lattice magnet. By combining several approaches we conclude that this system is most likely ordered for all values of spin, S, with a two-fold degenerate valence-bond solid being the ground state for small S. We show next that the Ising antiferromagnet with a weak four-spin exchange, equivalent to square ice with the leading quantum dynamics, exhibits analogous plaquette order. As a byproduct of this analysis we obtain, in the system of weakly coupled ice planes, a sliding phase with XY symmetry; at intermediate couplings, long range “anti-ferroelectric” order is stabilized. 相似文献
992.
Journal of Statistical Physics - 相似文献
993.
Christian J. Bordé Claus Lämmerzahl Ernst M. Rasel 《General Relativity and Gravitation》2004,36(10):2193-2196
994.
Potassium aluminophosphate glass with the composition 30 K2O-20 Al2O3-50 P2O5 (wt %) doped with four-valence vanadium was prepared and analyzed. Some physicochemical properties of the glass obtained
and its absorption and luminescence spectra were investigated at 300 K. The existence of oxovanadium ions in the prepared
glass was proved on the basis of the electronic absorption data. The bands observed in the electronic absorption spectrum
were assigned to the e→b
1 and e→a
1 transitions. Intense luminescence of four-valence vanadium in the wavelength range 800–1100 nm was found. The average luminescence
decay time amounts to 12 μs.
__________
Translated from Optika i Spektroskopiya, Vol. 96, No. 6, 2004, pp. 926–928.
Original Russian Text Copyright ? 2004 by Batyaev, Linnikov, Lipatova. 相似文献
995.
O. V. Andreeva V. G. Bespalov A. L. Pyait V. N. Sizov A. S. Cherkasov 《Optics and Spectroscopy》2004,96(2):149-156
The results of a complex investigation of the recording of dynamic holograms by pulsed radiation with a duration of 20 ns and 300 ps in fullerene-containing media based on porous glasses and polymethyl methacrylate matrices are reported. Spectral analysis of these media in the range 300–700 nm was performed. The efficiency of hologram recording was found to relate with the occurrence of a band at 330 nm in the absorption spectrum of a medium. It is shown that dynamic holograms can be recorded in the fullerene-containing media by nanosecond and picosecond pulses. In the latter case, holograms arise mainly due to a change in the electronic polarizability of fullerene molecules, which is almost inertialess. The results obtained can be used in the development of ultrafast switching devices based on dynamic holograms. 相似文献
996.
N. A. Borisevich S. L. Dziarzhytski V. A. Povedailo D. L. Yakovlev 《Optics and Spectroscopy》2004,96(6):819-823
The spectra of the fluorescence excitation within the rotational contours of the bands of the pure electronic long-wavelength S 0-S 1 transitions of jet-cooled indole and carbazole molecules and their complexes with water are measured. For the carbazole-water complex, a contour with three maxima is registered, which is possibly related to the occurrence of two isomers, differing in a slight displacement of hydrogen between the nitrogen atom of the imine group of carbazole and the oxygen atom of the water molecule. The degrees of polarization of integral fluorescence upon excitation within the rotational contours of the S 0-S 1 electronic transition bands of the above molecules and their complexes with water are determined for the first time. The coincidence of the calculated (7.7%) and measured (7.3%) values of the degree of polarization upon excitation in the rotational Q branch of the b L 1-A electronic transition of indole confirms the accepted intramolecular orientation of the transition dipole moment at an angle of 38.3° with respect to the principal axis of inertia A. Upon excitation of indole, its complex with water, and carbazole into the P and R branches, the measured and calculated degrees of polarization are also close to each other and amount to 2–3%. This confirms the occurrence of contributions to the fluorescence polarization due to the rotations of the indole molecules around the principal axes of inertia A and C. 相似文献
997.
998.
It is experimentally demonstrated that second-order polarizability gratings preliminarily recorded using bichromatic light in a phosphate glass can be amplified under the action of monochromatic radiation. The amplification effect takes place irrespective of the polarization and direction of propagation of the amplifying radiation and is achieved at various wavelengths. The phenomenon is related to the asymmetry of optical transitions between local centers in an isotropic medium in the presence of electric field. It is theoretically shown that this system may feature the formation of alternating electric field domains with dimensions depending on the grating amplitude. 相似文献
999.
A fractal-like structure of the domain boundaries was revealed in “overcritical” uniaxial Permalloy magnetic films. The fractal dimension of domain boundaries at the film surfaces was determined as a function of the film thickness. It is shown that the phase transition between the two possible types of fractal-like structures is accompanied by a jump in fractal dimension.
相似文献1000.