中国物理B

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SOLVABLE BOSON-FERMION MODEL FOR MIXED-VALENCE SYSTEMS

马选荣, 刘伍明, 赵宏伟, 蒲富恪

1997 (1): 1-5. doi: 10.1088/1004-423X/6/1/001

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Using the Bethe ansatz technique, the exact eigenstates of the Hamiltonian of the boson-fermion model for mixed-valence systems are constructed. The Bethe ansatz equations are obtained from the periodic boundary conditions.

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THE MULTIPLE IONIZATION OF ARGON INDUCED BY PARTIALLY STRIPPED CARBON IONS

蔡晓红, 申自勇, 陈熙萌, 刘兆远, 马新文, 刘惠萍, 侯明东

1997 (1): 6-12. doi: 10.1088/1004-423X/6/1/002

摘要 ( 1241 )

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The cross section ratios of the double, triple and quadruplicate ionization to the single ionization of argon by 1.5-7.5 MeV partially stripped carbon ions are measured by using time-of-flight technique. The Auger transition and the charge exchange process in the multiple ionization of argon are studied. The ratios of cross sections of the direct multiple ionization to those of the direct single ionization are obtained by subtracting the parts of the Auger transition and the charge exchange process from the measured data. It is found that the cross section ratios of the direct multiple ionization to those of the direct single ionization are in good agreement with the predicted mniti-step (ν/q_eff)^-2n+2 law.

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ELECTROMAGNETICALLY INDUCED FOCUSING IN A Λ-TYPE MEDIUM

龚尚庆, 徐至展

1997 (1): 13-17. doi: 10.1088/1004-423X/6/1/003

摘要 ( 986 )

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Electromagnetlcally induced transparency (EIT) in an inhomogenously broadened medium consisting of Λ-type three-level atoms has been analyzed. It is shown that the A system can induce a transparency of the medhun when the probe laser and the coupling laser have the same frequency detunings (including zero). Across the EIT window, the radial variation of the strong coupling laser radiation may lead to electromagnetically induced focusing or defocusing of the weak probe laser at separate probe frequency detuning points.

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GENERATION OF MULTI-WAVELENGTH VISIBLE LIGHT IN Er³⁺-DOPED AND Er³⁺/Yb³⁺-DOPED SINGLE-MODE OPTICAL FIBER PUMPED AT 1313 nm

胡巍, 刘东峰, 陈国夫, 王贤华, 候洵

1997 (1): 18-23. doi: 10.1088/1004-423X/6/1/004

摘要 ( 1139 )

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We report the generation of multi-wavelength visible light through amplified spontaneous emission (ASE) in Er³⁺-doped and Er³⁺/Yb³⁺-doped germanosilicate single-mode optical fiber pumped by a Nd:YLF laser at 1313nm. In the Er³⁺-doped fiber, the intense multi-wavelength blue emission hnes around 463-510nm corre-spond to transitions born ²G_7/2 etc. excited states to the metastable ⁴I_13/2 state, and their pumping mechanists is aecomphshed by a stepwise four-photon absorption. Some emission hnes in this wavelength region are attributed to the three-wave sum-frequency process of 1313 and 1530nm (corresponds to ⁴I_13/2 -⁴I_15/2). The intense green emission hnes at 525 and 540 nm are also observed in the Er³⁺-doped fiber. In the Er³⁺/Yb³⁺-doped fiber the blue and green lines are very weak compared with those in the Er³⁺-doped fiber.

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POWDER NEUTRON DIFFRACTION STUDIES OF THE CRYSTALLOGRAPHIC AND MAGNETIC STRUCTURE OF Ho₂Fe₉Ga₈ and Ho₂Fe₉Ga₆AI₂

成东风, 勾成

1997 (1): 24-27. doi: 10.1088/1004-423X/6/1/005

摘要 ( 1031 )

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The crystallographic and magnetic structures of Ho₂Fe₉Ga₈ and Ho₂Fe₉Ga₆AI₂ were studied by powder neutron diffraction at room temperature. The atom fractional occupancies of Ga and Al and the magnetic moments of Ho and Fe were obtained by using Rietveld analysis program. The magnetic structures of the two samples show an easy-axis anisotropy, with the Fe magnetic moment being ferrimagneticlly coupled to those of Ho.

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STUDY ON THE CATHODE DEPOSIT PRODUCED IN THE PROCESS OF CARBON ARC DISCHARGE

李凡庆, 陆斌, 左健, 陈志文, 贾云波, 卢江, 张庶元, 周贵恩

1997 (1): 28-34. doi: 10.1088/1004-423X/6/1/006

摘要 ( 999 )

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The cathode deposit produced by carbon are discharge wae studied by scanning electron microscopy, high resolution electroa microscopy, X-ray diffraction and Raman spectroscopy. The results indicate that the stacking of hexagonal carbon layer in the discharged graphite is different from the ABAB stacking sequence in graphite, and that carboy nanotube is a kind of graphite-like micro-crystal with a low-dimensional structure.

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PHASE TRANSITION IN A NONEQUILIBRIUM POTTS MODEL WITH COMPETING DYNAMICS: A MONTE-CARLO STUDY

郭文安, 杨展如

1997 (1): 35-39. doi: 10.1088/1004-423X/6/1/007

摘要 ( 999 )

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The nonequilibrium steady state of three-state Potts model evolving under combined Glauber dynamics at temperature β^-1 and Kawasaki dynamics at β′= 0 is studied by Monte-Carlo simulations. As the exchange rate p increases, the phase transition changes from second to first order. The critical exponents of second-order transition are independent of p, and the critical properties for different p belong to the same universality class.

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ELECTRONIC STRUCTURE OF Hg_0.8Pb_0.2Ba₂Ca₂Cu₃O_8+δ: THE ROLE OF Pb DOPING, OXYGEN DOPING AND HIGH PRESSURE

吕劲, 章立源, 郝学军

1997 (1): 40-51. doi: 10.1088/1004-423X/6/1/008

摘要 ( 1004 )

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The effects of Pb doping, oxygen doping ($\delta$= 0.1,0.2,0.4 and 0.5) and high pressate (4, 8, 15 and 20GPa) on the electronic structure of Hg_0.8Pb_0.2Ba₂Ca₂Cu₃O_8+δ have been examined by the recursion method. Our calculations show that Pb doping only decreases the hole concentration slightly and oxygen doping increases the hole concentration monotonically and significantly as δ varies from 0 to 0.5, with each excess oxygen atom contributing about 1.7 holes to the CuO₂ layers. The optimal δ is estimated to be around 0.4, The hole conceatration increases initially with pres-sure but decreases as P > 8GPa (i.e., dn/dP does change sign at ～ 8GPa). The suppressed T_c(P) by Pb substitution has to be described in the modified Neumeier's model.

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STRUCTURE AND PHOTOELECTRIC PROPERTIES OF HYDROGENATED AMORPHOUS SILICON-GERMAN-IUM ALLOYS PRODUCED BY HIGH HYDROGEN DILUTION METHOD

徐骏, 陈坤基, 冯端, 宫崎诚一, 广濑全孝

1997 (1): 52-56. doi: 10.1088/1004-423X/6/1/009

摘要 ( 1109 )

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A series of hydrogenated amorphous silicon-germanium alloys have been fabricated by high hydrogen dilution method. The Ge content in the film increasea from 0.4 to 0.8 and the corresponding optical bandgap is in the range of 1.48-1.22eV. The photoconductivity is 3.6×10^-6 S/cm and photosensitivity is as high as 7.3×10³ at an optical bandgap of 1.48eV. The deterioration of photoelectric properties with increasing Ge content could be attributed to the decrease of the bonded hydrogen content and the inhomogeneous structure in the alloy network.

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ELECTRON SPIN RESONANCE CHARACTERISTICS OF NITROGEN-DOPED FULLERENE

陈光华, 谢二庆, 张兴旺

1997 (1): 57-64. doi: 10.1088/1004-423X/6/1/010

摘要 ( 1038 )

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The nitrogen-doped fullerene has been obtained by arc discharge between two high-purity graphite rods in the atmosphere of N₂ and He, The electron spin resonance(ESR) characteristics of N-doped fullerene have been investigated. The results show that the ESR spectra of N-doped fallerene axe composed of two parts, a paramagnetic signal of N-center and a paramagnetic signal of C-center, For comparing with N-doped fullerene, we have also studied ESR spectra of C₆₀ powder, C₆₀ sublimed film and H-doped C₆₀ film. For C₆₀ powder and H-doped C₆₀ film, their in situ ESR. measurements are carried out at various temperatures, and reasonable explanations are proposed.

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A STUDY OF RAMAN SCATTERING AND INFRARED ABSORPTION SPECTRUM IN A NEW SERIES OF MERCURY-BASED HIGH-T_c SUPERCONDUCTOR (Hg,Mo)Sr₂(Y_1-xCa_x)Cu₂O_6+δ

许存义, 唐凯斌, 左健, 徐孝文, 朱警生, 钱逸泰, 张裕恒

1997 (1): 65-69. doi: 10.1088/1004-423X/6/1/011

摘要 ( 992 )

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Lattice vibrations of the (Hg,Mo)Sr₂(Y_1-xCa_x)Cu₂O_6+δ—a new series of mercury-based high-T_c superconductor are analyzed with the aid ofgroup theory. The vibrations of species are given. They are 4A_1g+ B_1g+ 5E_g+ 7A_2u + B_2u+ 8E_u. The 4A_1g, B_1g and 5E_g modes are Ramma active, the 6A_2u and 7E_u are infrared active. Phonon vibration characteristics of the samples are studied using Raman scattering and infrared absorption spectra. The experimental results show that the typical phonon vibrational modes appear mainly at 145, 320, 440, 578, 592 and 645cm^-1, The intensities of the 145, 320, 440, 578 and 645 peaks decrease with increasing Ca content x and the position of 645 peak moves to higher wavenumber slightly. In this article, the phonan modes are assigned and their variation behavior with increasing Ca content x are discussed.

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