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91.
Shou-Shu Gong 《Physics letters. A》2008,372(13):2322-2325
By means of the density matrix renormalization group (DMRG) method, the static spin structure factors and the magnetization plateaus of the trimerized Heisenberg ferromagnet-ferromagnet-antiferromagnet and antiferromagnet-antiferromagnet-ferromagnet spin chains in the presence of a magnetic field are elaborately studied. It is found that in the plateau states, the static structure factor with three peaks does not vary with the external magnetic field as well as the exchange couplings; the spin correlation function behaves as a perfect sequence and has a simple relation with the magnetization per site. An approximate wave function for the plateau states is proposed, and a picture based on the valence-bond-solid states is presented in order to understand the origin and the total number of the magnetization plateaus, which are shown to be in agreement with the DMRG results. 相似文献
92.
The magnon energy bands are studied for a four-layer ferromagnetic superlattice, with regard to the effects of the competition between the anisotropy and the spin quantum number. A special attention is also paid on the effects of the symmetry of the system. It is found that three modulated energy gaps exist in the magnon energy band along Kx direction perpendicular to the superlattice plane. The magnetic anisotropy affects significantly the magnon energy gaps. The zero energy gap Δω23 correlates with the conditions between anisotropy constants, D1+D3=D2+D4 and D1=D3 (or D2=D4), while the disappearance of the magnon energy gaps Δω12 and Δω34 corresponds to a translational symmetry of x-direction in a unit cell. When the parameters of the system deviate from these conditions, the energy gaps Δω12, Δω23 and Δω34 become larger. There is a competition effect of the anisotropy and the spin quantum number on the magnon energy gaps Δω12 and Δω23. When the symmetry of the system is higher, the competition can achieve a balance to cause the zero energy gap. 相似文献
93.
X.-Z. Yuan K.-D. Zhu H.-S. Goan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):375-380
In the thermodynamic limit, we present an exact
calculation of the time dynamics of a central spin coupling with
its environment at finite temperatures. The interactions belong to
the Heisenberg XY type. The case of an environment with finite
number of spins is also discussed. To get the reduced density
matrix, we use a novel operator technique which is mathematically
simple and physically clear, and allows us to treat systems and
environments that could all be strongly coupled mutually and
internally. The expectation value of the central spin and the von
Neumann entropy are obtained. 相似文献
94.
We propose a scheme for producing high gain recombination X-ray lasers on hydrogen-like Balmer transitions by irradiating fibre targets with a 2 ps Chirped Pulse Amplification CPA beam of a Nd-glass laser facility. Very high gain coefficients for H-like C, N, O, F, Na Balmer transitions are predicted. The optimum electron density and temperature for maximum gain operation scale approximately asN
e 4 × 1013
Z
7 cm–3 and Te 7 × 10–3
Z
4 eV, respectively, at the time when maximum lasing gain appears. Significant improvement in gain performance of recombination X-ray lasers is predicted by using CPA ps pulse drivers. 相似文献
95.
Motivated by the successful synthesis of several molecular quantum spin rings we are investigating whether such systems can host magnetic solitary waves. The small size of these spin systems forbids the application of a classical or continuum limit. We therefore investigate whether the time-dependent Schrödinger equation itself permits solitary waves. Example solutions are obtained via complete diagonalization of the underlying Heisenberg Hamiltonian. 相似文献
96.
A. R. Prüg A. Glinz J. E. Balmer Y. Li E. E. Fill 《Applied physics. B, Lasers and optics》1996,63(2):113-116
The dependence of the intensity of the 3p—3s,J = 0–1 lasing line at 32.6 nm in neon-like titanium on the prepulse level has been investigated experimentally. Titanium slabs were irradiated with 1.315 µm/450 ps pulses from the Asterix IV iodine laser using a defined prepulse of 5.2 ns before the main pulse. It is found that for pump energies close to the minimum energy for which lasing is observed, a prepulse level of order 0.5% gives the highest XUV laser intensity, whereas a higher prepulse level, of order 10% and more, is required for optimum XUV lasing far above the threshold. For a 2.7 cm long titanium target lasing was observed down to a pump irradiance of 2.5 TW/cm2 (50 J/450 ps) for the 0.5% prepulse. 相似文献
97.
The effective interaction between gauge vortices on a square lattice is revealed to be attractive at short distance and oscillate
between repulsion and attraction at long distance. It is analyzed that the strong attraction at short distance makes the gauge
vortices cluster at a given flux concentration; while the oscillatory nature in the interaction potential is the consequence
of the existence of the electron Fermi surface in the nonuniform flux phases states. 相似文献
98.
Z. Bor B. Racz G. Szabo D. Xenakis C. Kalpouzos C. Fotakis 《Applied Physics A: Materials Science & Processing》1995,60(4):365-368
A subpicosecond KrF laser system (248 nm, 0.5 ps) was used as a light source for ablation of PMMA Mylar and Kapton. The time-dependent reflectivity of the light-induced plasma mirror as measured by 496 nm, 0.5 ps long probe pulses showed an increase of up to 94% with 0.4–1 ps rise time and 10–15 ps fall time. The highdensity plasma mirror shows perfect optical quality, and seems to be a promising light-controlled ultrafast switch for UV and visible light. The spectrum of the UV light reflected from the ablated spot is blue shifted by 0.5 nm and shows 1 nm broadening. 相似文献
99.
Zafer Gedik 《Solid State Communications》2006,138(2):82-85
We study an analytically solvable model for decoherence of a two spin system embedded in a large spin environment. As a measure of entanglement, we evaluate the concurrence for the Bell states (Einstein-Podolsky-Rosen pairs). We find that while for two separate spin baths all four Bell states lose their coherence with the same time dependence, for a common spin bath, two of the states decay faster than the others. We explain this difference by the relative orientation of the individual spins in the pair. We also examine how the Bell inequality is violated in the coherent regime. Both for one bath and two bath cases, we find that while two of the Bell states always obey the inequality, the other two violate the inequality at early times. 相似文献
100.
The pairwise entanglement between neighboring spins in a general mixed-spin chain with arbitrary spins S and 1/2 is investigated in the thermodynamical limit. The entanglement is witnessed by the magnetic susceptibility which determines a characteristic temperature for an entangled thermal state. The characteristic temperature is nearly proportional to the interaction J and the mixed-spin S. The bound of negativity is obtained on the basis of the magnetic susceptibility. It is found that the macroscopic magnetic properties are affected by the quantum entanglement in the real solids. 相似文献