Vol. 40, No. 7 (1991)
1991-04-05
1991, 40 (7): 1025-1030.
doi: 10.7498/aps.40.1025
Abstract +
The oscillator strengths and lifetime for some states of Mg are calculated by using model-potential wavefunctions. After comparing the fesults with previous theretical and experimental data, it is concluded that for many states with weaker configuration mixing, these quantities can be well calculated by such singe configuration wavefunctions.
1991, 40 (7): 1034-1041.
doi: 10.7498/aps.40.1034
Abstract +
In a laser field, for the electron scattered by Coulomb potential, when the wave function is expanded by Floquet partial wave, the Sehrodinger equation separates into the radial form by separation of variables. The system of equations for the radial wave function is infinitely coupling linear second order differential equations. When weak laser field is considered as a pertubation, the equations can be reduced into second order ordinary differential equations and they are integrable.The radial wave functions S-matrix and the cross section are obtained. Finally, the resonance lines appear for differential cases of polarizations no matter whether the dipole approximation is used. The resonance energies, the intensities of resonance lines are obtained.
1991, 40 (7): 1042-1048.
doi: 10.7498/aps.40.1042
Abstract +
In this paper, we investigate the time evolution of the atomic operators of a two-Ievel atom interacting with the field via a two –photon Process within and without the rotating-wave approximation (RWA) by means of non-relativestic QED. We also verified that the virtual photon field is the cause for quantum chaos embodied by the periodic decay and revival effect of the atom using the numerical and analytic methods, and discussed the reason of neglecting the influence of the virtual photon field on the revival time.
1991, 40 (7): 1049-1057.
doi: 10.7498/aps.40.1049
Abstract +
In this paper, we have studied the nonlinear interaction of two cascade three-level atoms with singe mode field. The results show that the cooperative emission of two atoms can translate into synchronous when the strength of exciting field reaches a certain threshold. That is self-oganization may occur in many-atom system to form a “large atom system” at the threshold, producing synchronous ordered emission. Meanwhile, the second-order correlation degree of two-atom system is lager than that of single atom system due to the synchronous emission effect, i.e.bunching is strong but antibunching is weak. Moreover, the deeper squeezing of two-atom system is obtained since many-photon processes become stronger, and the strength of exciting field is required to be also stronger.
1991, 40 (7): 1065-1073.
doi: 10.7498/aps.40.1065
Abstract +
In solid laser resonator the dioptric strength of the thermal focusing lens, l/f, as a dynamic factor of the resonator, has great influence on the operation characters of the resonator. In this paper, using the transformation-circle diagrammatic approach, a dynamical analysis on the stability, character of output power and mode property of the solid laser resonator is represented in detail. Their relations on the dynamic factor are also derived.
1991, 40 (7): 1074-1079.
doi: 10.7498/aps.40.1074
Abstract +
By means of a new formalism of the Kronig-Ponney model developed recently, the third order nonlinear optical effect of intersubband transition In superlattices is studied. It is shown that there is a general relation between optical saturation intensity and tunnel bandwidth. The physical mechanism of this relation is analyzed.
1991, 40 (7): 1080-1085.
doi: 10.7498/aps.40.1080
Abstract +
The properties of vibrational states for one-dimensional quasi-lattice, specially, properties of critical states are studied. Some methods describing different vibrational states are given.
1991, 40 (7): 1086-1094.
doi: 10.7498/aps.40.1086
Abstract +
This paper is devoted to the study of phonon and melting property of two-demensional PeLrose lattice with five-fold rotational symmetric axis. We introduce a similarity transformation which transforms the dynamical matrix into a block-diagonal matrix, which helps to determine analytically the degeneracies of the modes of the phonon spectra and reduce the numerical calculation. It is found that two thirds of the modes are doubly degenerate and theremains are nondegenerate. By using the atomic mean-square displacement criterion, we study the melting property of the two-demensional Penrose lattice. We find that boundary atoms always have lower melting temperature than that of bulk, and when the interaction among atoms is larger, the system will have a higher melting temperature.
1991, 40 (7): 1095-1100.
doi: 10.7498/aps.40.1095
Abstract +
In temperature range of 20K to 300K, we measured photoluminescence spectra of heterogeneous J-aggregate Langmiur-Blodgett (LB) films made of three kinds of cyanine dye. With temperature reduced, while the intensity of J-peak, the zero phonon line increased, anomalous enhancement of the phonon sideband was observed. Analysis shows that J-aggregate LB films are of characteristics like that of low dimensional crystal, they have strong phonon coupling and nonradiative transition plays important role.
1991, 40 (7): 1110-1115.
doi: 10.7498/aps.40.1110
Abstract +
The experimental method for studying interface atomic structure between amorphous layer and crystal by MeV ion scattering and channeling is described. This method is applied to study the Al_2_O_3_/AI(100) interface . Thin AI oxide film are formed on clean AI(100) surface in pure oxygen ambience at 400℃. The experimental results show that the composition of the oxide film is precisely Al_2_O_3 and the interface between AI oxide film Al(100) bulk is very sharp, the reconstructive layer under the Al_2_O_3 film is no more than one monolayer. Monte carlo simulations indicate the distance between displaced Al atoms on the reconstructive layer and Al(100) axis is 0.18A. At room temperature, the oxygen adsorption layer of Al(100) is primarily stoichiometric AlO at low surface coverages.
1991, 40 (7): 1116-1120.
doi: 10.7498/aps.40.1116
Abstract +
Using ASED-MO method and cluster models, the chemisorptions energy of Li on Si(100) 2XI surface and the interaction between two adsorbed Li atoms are calculated. A new model which Can be used to explain the transition from Si(100)-Li(2Xl) to Li(1Xl) in the 1 monolayer range is proposed.
1991, 40 (7): 1121-1128.
doi: 10.7498/aps.40.1121
Abstract +
Ge_xSi_1-x_/Si strained-layer superlattices were grown on Si(100) substrates under different temperatures by molecular beam epitaxy. Methods such as reflection high energy electron diffraction, X-ray double crystal diffraction, Rutherford back scattering, transmission electron microscopy and Raman scattering have been applied to study the growth and characteristics of the Ge_xSi_1-x_/Si superlattices. The result show that the optimum growth temperature are different for superlattices with different composition, the small the x the higher the growth temperature, and vice versa. For x=0.1-0.6, the Ge_xSi_1-x_/Si superlattices with flat interfaces, good crystal perfection and uniform periodicity can be obtained with growth temperature in the range of 400一600℃.
1991, 40 (7): 1129-1133.
doi: 10.7498/aps.40.1129
Abstract +
We calculate the lattice heat capacity of layered material based on simple with cubic structure and Born potential. It is shown that interface states affect the lattice capacity obviously when the thickness of layer is relatively small (less than several tens of single la-years). With the increasing of thickness of the layer, the lattice capacity decreses and is nearly independent of interface states and thickness of the layer. We also give a comparison of the lattice capacity of aperiodic superlattice with that of periodic superlattice.
1991, 40 (7): 1134-1140.
doi: 10.7498/aps.40.1134
Abstract +
Solid state reaction interdiffusion of Fe-Ti multilayer modulated films was investigated by means of dynamic in situ X-ray diffraction. With this method, the measurement of the X-ray modulation peak intensity was relatively accurate and the shift in X-ray modulation peak position was also observed. The interdiffusion coefficients of Fe-Ti modulated films were calculated at different temperatures. Plots of the interdiffusion coefficients versus time at different temperatures were given, According to the variation rate of D vs.t, the activation energy Q relative to viscosity relaxation was calculate to be 8.3±0.2 kal/mol.
1991, 40 (7): 1141-1148.
doi: 10.7498/aps.40.1141
Abstract +
Under Bose and non-Bose approximations, the squeezing, antibunching and sub-Poissonian statistics of one-exciton and two-exciton in the Dicke and Fock superposition states are discussed. The recombination radiation of excitons in these superposition states can also have these non-classical effects. The results obtained in various situations are compared and explained.
1991, 40 (7): 1149-1156.
doi: 10.7498/aps.40.1149
Abstract +
The collective excitations of three-dimensional tight-binding electron gas system have been studied in the case of three different kinds of structures (s.c.,f.c.c.,b.c.c.). By random phase approximation, we obtain the matrix formulation of the theory.
1991, 40 (7): 1157-1161.
doi: 10.7498/aps.40.1157
Abstract +
Using the multi-channel generalization of Landauer formula, we investigate the adiabatic transport and the Ohmic transport of two unequal narrow constrictions in series with a closed cavity in between. It is shown that the adiabatic transmission leads to the nonadditivity of constriction’s resistances, and the completely incoherent transport obeys the Obmic addition rule.
1991, 40 (7): 1162-1173.
doi: 10.7498/aps.40.1162
Abstract +
The ground states of phonons in dissipative quantum tunneling system and their influences on the localization delocalization transition are investigated by a variational approach. We find that: 1.There are two kind of influences, displacement and deformation, on phonon describe both these influences. 2. The localization-delocalization transition depends on the choice of phonon ground state. The transition will occur at strong coupling as the energy of the ground state decreases.
1991, 40 (7): 1174-1178.
doi: 10.7498/aps.40.1174
Abstract +
Two high T_c_ superconductor YBa_2Cu_3O_7_ thin films, the zero resistance temperature of which were 82K and 7lK respectively, were selected for measurement about resistance broadening. The difference in thermal activation energy of the two samples was analyzed with Arrhenius law auggested by Palstra. We found that the activation energy decreased depending upon increasing magnetic field. The irreversibility line was B * -(l -T*/T_c_)**3/2 deduced from our data.
1991, 40 (7): 1179-1185.
doi: 10.7498/aps.40.1179
Abstract +
Based on the fact of the existence of a small amount itinerant electrons, a new theoretical model giving rise to magneto-crystalline anisotropy in compound Nd_2Fe_14_B is presented in this paper. It is proposed that a combined effect on Nd一ion coming from both the crystal field of ligands and the electric field of itinerant electrons results in the anisotropy in the compound. An approach of calculating the interaction between itinerant electrons and central Nd-ion given. The magneto-crystalline anisotropy of Nd-ion and its temperature dependences are calculated based on the model. The results are in good agreement with the experiments, and also give explanation to the spin reorientation Phenomenon in the compound.
1991, 40 (7): 1186-1192.
doi: 10.7498/aps.40.1186
Abstract +
We have studied the structure and intrinsic magnetic properties of R_2Fe_17_C compound (R=Y,Sm,Gd,Tb,DyandEr), and compounds them with the corresponding R_2Fe_17_ compounds. The Curie temperatures of R_2Fe_17_C are about 200K greater than those of R_2Fe_17_. We discussed the variation of the structure and magnetism of the compounds due to introducing C atoms. Furthermore, Sm_2_(Fe_1-x_Co_x_)_17_C compound have also been studied.
1991, 40 (7): 1193-1200.
doi: 10.7498/aps.40.1193
Abstract +
The Faraday rotation caused by electronic transitions between the 4f and 5d states of Ce ions in paramagnetic CeF_3_ crystals is calculated. The crystal field is an important perturbation on the energy levels. An external magnetic field, together with an additive magnetic field introduced phenomenologically in our paper, would spilt every 4f state into two sublevels. The dipole transitions between these sublevels, and 5d states induce the Faradap effect. The Verdet constant at 0.6328 um in the temperature range of 60-300K is obtained. It is shown that our calculation is in good agreement with experiment.
