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Volume 4 Issue 11
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Original Articles
POINT-CONTACT TUNNELING INVESTIGATION OF THE SUPERCONDUCTORS IN Y-Ba-Cu-O SYSTEM
TAO Hongjie, CHEN Yingfei, LÜ, Li, ZHAO Bairu, SHI Yinhuan, LU Yong, WANG Huisheng, ZHAO Yuying, LI Lin
Chin. Phys. Lett. 1987, 4 (11): 481-484 .  
Abstract   PDF(pc) (70KB) ( 312 )
Point-contact tunneling measurements of the oxide superconductor Y-Ba-Cu-O were carried out with both Nb and Mo tips. An energy gap, Δ=18.5meV and 2Δ/kTc=4.7 were obtained. The result is consistent with the strong-coupling theory. The tunneling conductance curves indicate a granular feature of the sample.
MAGNETIZATION MEASUREMENTS OF HIGH Tc SUPERCONDUCTING Ba-Y-Cu-O SYSTEM
SHI Yinhuan, ZHAO Bairu, WANG Huisheng, LU Yong, ZHAO Yuying, XU Po, LI Lin
Chin. Phys. Lett. 1987, 4 (11): 485-488 .  
Abstract   PDF(pc) (55KB) ( 388 )
The magnetization M(T) at a fixed field, the magnetization M(H) at different temperatures of the Ba-Y-Cu-O samples with zero resistance at 91.5K have been measured. The results show that Ba-Y-Cu-O is a type-II superconductor. We also present the anomaly of M(T) at low temperature. At T approaching OK, M(H) changes from negative to positive. The relationship between the area of magnetic hysteresis loop and the critical current density is discussed.
NEGATIVE U CENTERS AND LOCAL LATTICE VIBRATION IN CHARGE DISPROPORTIONATION SYSTEM
CHEN Changfeng
Chin. Phys. Lett. 1987, 4 (11): 489-492 .  
Abstract   PDF(pc) (42KB) ( 369 )
The interaction between negative U center and conduction electron in charge disproportionation system is studied. We point out that the dissociation and formation of negative U centers will cause local lattice vibration, from which electron-phonon interaction may result and this has great influence on the superconductivity of the system.
ZERO RESISTANCE ABOVE 90K IN SUPERCONDUCTING OXIDE Tm-Ba-Cu-O
ZHANG Qirui, QIAN Yitai, CHEN Zuyao, GUAN Weiyan, ZHAO Yong, PAN Guoqiang, CAO Liezhao, XIA Jiansheng, ZHANG Han, HE Zhenghui, YU Daoqi, ZHANG Minjian, SUN Shifang, FANG Minhu, ZHANG Tao
Chin. Phys. Lett. 1987, 4 (11): 493-496 .  
Abstract   PDF(pc) (45KB) ( 400 )
Superconducting transition has been observed by electrical resistance and a.c. magnetic susceptibility measurements in TmxBa1-xCuO3-y with x=0.6 and 0.7 and y>0. The highest Tc of the samples measured is observed in Tm0.6- Ba0.4CuO3-y which has the Tc(mid)=91K with ΔTc=0.5K, and Tc(ρ=0)=90.1K. The a. c . magnetic susceptibility measurements show a very strong diamagnetism at the temperature of resistive midpoint.
MONTE CARLO SIMULATION OF SU( 3 )xSU( 3 ) CHIRAL MODEL ON A 2-DIMENSIONAL RANDOM LATTICE
LI Wenzhu, YING Heping, ZHANG Jianbo
Chin. Phys. Lett. 1987, 4 (11): 497-500 .  
Abstract   PDF(pc) (52KB) ( 325 )
Monte Carlo (M-C) measurements of the SU(3)xSU(3) chiral model defined on a NxN 2-dimensional(2-D) random lattice are presented. Calculations are made of energy, specific heat and order parameter per spin on the 10x10, l2x12 and 16x16 lattics. It is shown that the system enters a crossover region at β=4.75±0.10, but no evidences of phase transition are obtained. It is found that our results are consistent with that of the 4-D gauge theory and the 2-D chiral model on the regular lattice.
X-RAY EMISSION SPECTRA FROM LASER-PRODUCED COBALT PLASMA
DONG Qi, LI Jiaming
Chin. Phys. Lett. 1987, 4 (11): 501-504 .  
Abstract   PDF(pc) (48KB) ( 385 )
Based on theoretical calculations by our non-relativistic configuration interaction computer code, we have successfully identified the x-ray spectra from the cobalt plasma produced by high-power laser. Here we focus on the spectra consisting of x-ray line emission from the N-like and C-like ions. Many new x-ray lines have been identified.
FERMION DYNAMICAL SYMMETRY MODEL OF 2s - ld SHELL
HAN Qizhi, WANG Jiajun, SUN Hongzhou*, LONG Guilu*
Chin. Phys. Lett. 1987, 4 (11): 505-508 .  
Abstract   PDF(pc) (42KB) ( 490 )
In the framework of shell model, we discussed the fermion dynamical symmetries in 2s-ld shell. Assuming the L-S coupling and the Wigner supermultiplet, we get a U( 24 ) fermion dynamical symmetry. All possible subgroup chains are discussed. We have found that 32S seems to exhibit U(5) dynamical symmetry.

QUANTITATIVE EVALUATION OF ISLAND SEPARATION AND ISLAND SIZE DISTRIBU TIONS IN CHEMISORPTION
ZHAO Lihua*, LUO Enzhou*, WU Naijuan, FENG Kean
Chin. Phys. Lett. 1987, 4 (11): 509-512 .  
Abstract   PDF(pc) (52KB) ( 318 )
The two-dimensional autocorrelation function of island separations for commensurately adsorbed overlayers is evaluated and used to calculate the angular profiles of the diffracted beams from arbitrary distribution of overlayer islands. Model calculations are made for a realistic surface. The results are compared to the low energy electron diffraction (LEED) measurement of O/W(112) system and quantitative structural information on the distribution of islands for overlayers is then extracted.
PARAMAGNETIC BEHAVIOR OF Nd2Fe14B SINGLE CRYSTAL
LIU Yihua*, ME Liangmo*, CHEN Huanchu, CHEN Fusheng
Chin. Phys. Lett. 1987, 4 (11): 513-516 .  
Abstract   PDF(pc) (47KB) ( 562 )
The paramagnetic parameters of the Nd2Fe14B single crystal were measured. In the temperature range from about 600K to 830K, the temperature dependence of the reciprocal susceptibility obeyed Curie-Weiss law, from which the effective magnetic moment for Fe atoms, 3.97μB/Fe atom, can be obtained.
NEUTRON DIFFRACTION STUDY OF SPIN REORIENTATION OF Nd15Fe78B7
HE Wenwang(HO Wen-wang), YANG Yingchang, CHEN Haiying, XING Feng, YANG Jilian*, ZHANG Baishen*, ZHOU Huiaing*, JIN Lan*
Chin. Phys. Lett. 1987, 4 (11): 517-520 .  
Abstract   PDF(pc) (45KB) ( 361 )
Using neutron diffraction and magnetic measurement, we have measured the canting angle of the iron spin in Nd15Fe78B7 compound with powder samples. The iron spins rotate away from the c- axis by 26°34' at 77K.

SCREENING TO CRYSTALLINE-ELECTRIC-FIELD IN RARE-EARTH INTERMETALLIC COMPOUND
LU Xiaojia, ZENG Xunyi
Chin. Phys. Lett. 1987, 4 (11): 521-524 .  
Abstract   PDF(pc) (36KB) ( 331 )
A derivation which avoids the complicated differential computation in calculating the crystalline electric field coefficients for a non-Coulombian central potential is suggested. Using the result obtained and within the linear screening model the variation of crystalline electric field coefficients for Nd3+ as a function of distance is presented.
THERMOELECTRIC POWER OF Y0.6Ba0.4CuO3-x
RANG Yaozhong, WANG Ruiping, MENG Guangyao, PENG Dingkung, WANG Jun, HU Xuelong, ZHANG Yuheng
Chin. Phys. Lett. 1987, 4 (11): 525-527 .  
Abstract   PDF(pc) (37KB) ( 319 )
The thermoelectric power of the high-temperature super-conductor Y0.6Ba0.4CuO3-x was measured as a function of temperature between 77-300K. A change in sign of thermoelectric power was observed around 205K. This indicates that the charge carriers are predominantly electrons at temperatures above 205K and positive carriers below 205K.till the temperature reaches that corresponding to zero thermoelectric power.
12 articles