INFLUENCE OF SPIN AND CHARGE FLUCTUATIONS ON THE HIGH-Tc SUPERCONDUCTIVITY

In the framework of the weak coupling theory of superconductivity, we have proved that spin and charge fluctuations in the high-T_c superconductors can pro-duce respectively, pair-breaking and pair-forming effects on the superconductivity resulting from the "generalized BCS mechanism". With the coupling constant for spin fluctuations larger than that for charge fluctuations, they combine to produce a temperature-dependent effective pair-breaking effect, which makes T_c decrease more rapidly than Δ(0), the superconducting gap at T=0, and therefore, enhances the ratio 2Δ(0)/T_c. This provides a reasonable physical interpretation for the relevant experimental results.     

非磁杂质对高Tc超导电性的影响

本文证明了在氧化物高T_c超导体的Anderson晶格模型中,由于序参量是能量的函数,非磁掺杂也具有拆对效应,在稀掺杂情况下,求出了T_c随杂质浓度增加而线性下降的规律,与实验结果相符,文中还计算了掺杂对超导态密度中能隙的影响,结果表明,当非磁掺杂浓度增加时,零温能隙的减小比T_c的下降慢得多,从而在转变为正常态之前可能不出现类似通常BCS超导体磁性掺杂的无能隙区。 关键词：     

BCS-van Hove方案与高温超导电性

基于BCS—van Hove机制,研究了非磁杂质对高温超导电性的抑制效应,考虑到双层耦合效应和三维耦合效应,将van Hove方案推广到多带BCS模型,计算了超导转变温度与化学势的关系,并与实验结果进行了比较。     

准二维玻色凝聚、氧空位、高温超导

本文从准二维玻色凝聚出发,研究了层状高温超导氧化物材料中,层厚度和氧空位对临界温度的影响。所得结论应用到YBa₂Cu₃O₇中,与已知的实验定性符合。 关键词：     

晶格振动、载流子与高温超导电性的关系

系统地从红外光谱的结果论述了晶格振动、载流子与高温超导电性的关系。指出,在高温超导体中,载流子对晶格振动的作用不是屏蔽作用,而是两者之间的局域强耦合相互作用,这种局域的耦合不同于普通的电声子耦合。在此基础上,通过理论和实验研究,论述了局域耦合强度及其整体效应与超导电性的关系。 关键词：     

INVESTIGATION OF THE EFFECT OF SLOW NEUTRON IRRADIATION ON HALOGEN-DOPED HIGH-Tc SUPERCONDUCTORS AND ITS MECHANISM

Irradiation effect of low-fluence (-10⁸ n/cm² ) slow neutrons on halogen-doped superconductors is presented in this paper. And the mechanism of the effect is also described from the viewpoint of nuclear physics for both fast and slow neutrons on high-temperature superconductors (HTSC). It is shown ex-perimentally and theoretically that slow neutrons of low fluence has a similar irradiation effect to that of fast neutron beams with an energy E_n>0.1 MeV and fluence 10¹⁶-10¹⁸ n/cm²-However,quite differ-ent mechanisms are involved in them: Fast neutrons transfer their energies through elastic scattering in HTSC, whereas slow neutrons give off their energies during the slow neutron capture (n,γ) reaction.     

THE EXCHANGE FLUCTUATIONS AND PARAMAGNETISM TO SPIN GLASS TRANSITION

In this paper, we introduce a quantity where N is the total number spins, to characterize the randomness of the partition function z. We point out, when Δ=0, the relation lnZ=lnZ is valid for the Sherrington-Kirkpatrick (SK) model,the generalized SK model. It is shown that this quantity can also be used to determine the spin glass transition temperature in the absence of extprnal field with zero average exchange J₀.     

高温超导体的磁化与磁滞损耗

利用三种临界态模型(Bean模型、Kim模型和指数模型),采用比较简单的方法,以Bi2223高温超导体为例,给出了平板状超导体的初始磁化曲线和磁滞回线的解析表达式.对不同温度和磁场下的磁化强度进行了编程计算,对计算结果进行讨论.利用推导的公式,讨论了温度和外加磁场对高温超导体的磁滞损耗的影响. 关键词： 磁滞损耗 磁通钉扎 高温超导体 临界态模型     

Mn、Ti掺杂对NaxCoO2体系超导电性和电荷有序化影响

本文研究了Mn、Ti掺杂对Na0.3Co1-xMxO2·1.3H2O超导电性和 Na0.5Co1-xMxO2材料电荷有序现象的影响.我们成功合成了Na0.7Co1-xMxO2(M= Mn和Ti,0≤x≤0.1)系列样品,并采用不同强度氧化剂氧化脱钠,分别获得Na0.5Co1-xMxO2和水合物Na0.3Co1-xMxO2·1.3H2O (0≤x≤0.1, M= Mn和Ti).X射线衍射分析表明所有样品都是比较好的单相,它们的晶格常数随着Ti和Mn的含量发生系列变化.物性检测显示Na0.3Co1-xMxO2·1.3H2O的超导电性随着Mn和Ti掺杂量的增加明显减弱,在Mn掺杂为x=0.02 或Ti掺杂为x=0.01时其超导电性消失;磁性检测发现随着掺杂量的增加,Na0.5Co1-xMxO2电荷有序态被逐渐破坏,其中掺Mn比掺Ti对电荷有序化行为的影响更为明显.     

EFFECT OF THERMAL TREATMENTS ON THE SUPERCONDUCTIVITY OF UNDOPED AND WO3 DOPED Y-Ba-Cu-O SYSTEM

Undoped and WO₃-doped Y-Ba-Cu-O ceramics have been slowly cooled in flowing oxygen or quenched in air from 900℃ to room temperature, after sintering at 900℃ for 3Oh in flowing oxygen. The ac susceptibility measurements show that the T_c of the quenched WO₃-doped Y-Ba-Gu-O superconductor can reach 88K, while the undoped Y-Ba-Cu-O ceramic quenched in air is a non-superconductor. X-ray diffraction data show that WO₃ does not enter into the YBa₂Cu₃O_7-x lattice but forms all impurity phase. The WO₃-doped YBCO specimens quenched in air consist of orthorhombic YBa₂Cu₃O_7-x phase and an impurity phase which increases with increasing WO₃ content. Raman spectra chow that oxygen contents are different for undoped and WO₃-doped samples. It la suggested that suitable doping with WO₃ can change the oxygen content and reduce the effect of thermal treatments on the superconductivity of Y-Ba-Cu-O system.     

CHARGE AND SPIN GAPS IN THE DIMERIZED HUBBARD MODEL

By using the bosonization and renormalization group methods, we have studied the low energy physical properties in the one-dimensional dimerized Hubbard model. The formation of charge and spin gaps is investigated both for the half-filled electron band and away from the half-filled band. The scaling laws of the charge and spin gaps with the dimerization parameterΔ and the repulsive interaction strength U are obtained.     

束缚电荷对玻璃材料二阶光学非线性的影响

对电场极化后薄膜材料与体材料二阶光学非线性的比较研究表明,二者具有相同的极化和弛豫特性．分析了束缚电荷的形成及其对二阶光学非线性的影响,定性地从理论上指出,由束缚电荷产生的电场对薄膜及体材料的极化和弛豫过程起了决定作用． 关键词： 二阶非线性 玻璃 极化 束缚电荷     

NEUTRON SPIN INTERFERENCE,PRINCIPLE OF SPINOR SUPERPOSITION AND INFLUENCE OF EARTH GRAVITY ON THE NSE

The interfererice between the spinor components of the potarized neutron beam passing through a Mezei-coil investiga-ted. The authors proposed a method to detect the phase shift of the spinor Components a to test the principle of the fermion spin superposition. The influence of the earth gravity on the spinor interference is considered. The results show that the Planck's constant h and the Newtonian gravitational constant G(or q) both are involved in the phase shift θ, which is independent of the neutron mass.     

MX络合物中电荷密度波和自旋密度波对三次谐波产生系数的影响

研究了电子-电子相互作用与电子-声子相互作用的竞争对MX络合物基态及三次谐波产生系数(THG)的影响。根据哈伯德模型,当电子-电子相互作用强度U不超过2t₀(t₀是最近邻的M原子d_z²和x原子Pz轨道间的跳跃能)时,可用Hartree-Fock(HF)近似来研究体系的状态,结果发现随着U的增大,体系会从电荷密度波(CDW)变为自旋密度波(SDW),相交点发生在U～1.2t₀,且是一级相变。在相变点     

Bi系超导体高Tc相的形成机制

本文研究Bi系超导体高T_c(2223)相的形成机制。提出Bi系氧化物超导体高T_c相的形成过程是:首先Sr-Ca-Cu氧化物(Ca_0.85Sr_0.15CuO₂)与低T_c(2212)相反应形成高T_c相的核,然后样品内2223相核通过象结晶学中晶体生长那样的方式长大成2223相晶粒。2223相成核过程中Sr-Ca-Cu氧化物的形成途径有两条:一条是通过固相反应 关键词：     

自旋波之间的散射对铁磁共振曲线的影响

本文讨论了k≠0自旋波间的散射对共振吸收曲线的影响,得到了吸收曲线的ι级矩的严格的表达式。用微扰法求出了在一级近似下对吸收曲线的改正。     

用自旋标记研究人参皂甙对血卟啉光敏作用的影响

本文首次合成和使用自旋标记的血卟啉氮氧自由基,研究了人参皂甙对HPD光敏作用的影响。发现在含水或含有人血清白蛋白的体系中,人参皂甙均具有明显的抑制HPD光氧化作用和促进HPD光还原氮氧自由基的作用。这可能与人参皂甙具有阻断或者清扫HPD敏化产生的¹O₂有关系。因此,人参皂甙在缓解HPD光敏毒性,保护正常组织不受损伤方面可能具有重要的意义。     

INFLUENCE OF OXYGEN UPON THE SUPERCONDUCTIVITY OF THE Pb-DOPED 2223 SUPERCONDUCTOR

The influences of oxygen content (by quenching from different temperatures in air or oxygen) and its re-distribution (by annealing in nitrogen at 200℃) on T_c and room temperature resistivity were studied. It was found that T_c as a function of oxygen content or charge carrier concentration exhibits a maximum. Upon oxygen re-distribution, the room temperature resistivity would always inclose but T_c would change in a complicated way. T_c increases for the oxygen-rich state and decreases for the oxygen-deficient state Internal friction measurements showed that there are two kinds of oxygen defects in the Bi₂-O₂ layers. One is the isolated oxygen interstitials and the other is oxygen vacancies on the excess oxygen chains. It is proposed that the isolated interstitial oxygen will produce a set of impurity states near the Fermi level, and will create holes on the Cu3d-O2p band through charge transfer from the Cu3d-O2p band to the impurity states. The content of the isolated oxygen interstitial is believed to be the major factor for determining the charge carrier concentration. Variation of T_c and room temperature resistivity with oxygen re-distribution is sat-isfactorily explained as to be induced by combination of oxygen interstitials with oxygen vacancies on the excess oxygen-chains.     

介观RLC电路中电荷和电流的量子涨落

发展了一种将有源RLC电路量子化的方法,在此基础上,研究了真空态下介观RLC电路中电荷、电流的量子涨落,特别是研究了电阻对量子涨落的影响.