高T_c氧化物超导体Bi(Pb)-Sr-Ca-Cu-O(F)的“不可逆线”

研究了高T_c氧化物超导体Bi(Pb)-Sr-Ca-Cu-O(F)体系的“不可逆线”。发现不可逆磁场H~*<120Oe时,H~*=1590(1—t)~3/2;当120Oe相似文献   

YBa2Cu3O7-δ外延薄膜的不可逆线与磁通玻璃线

在0—10T磁场范围内,系统地测量了YBa₂Cu₃O_7-δ外延薄膜处于磁场平行和垂直膜面两种情况下的R-T曲线和I-V曲线, 并对该样品的不可逆线和磁通玻璃线作了直接的比较.结果表明, 由不同约化电阻率判据给出的不可逆线和磁通玻璃线遵守相同的H∝(T(0)-T(H))ⁿ 关系.对于不可逆线, n=3/2,对于磁通玻璃线,n=4/3.不可逆线的位置不仅与判据有关而且与测量电流密度也有关,磁通玻璃线位于不可逆线的下方.探讨 关键词：     

Yba2Cu3O7-δ不可逆线与钉扎势的关联

本文分别测量了熔融织构YBa₂Cu₃O_7-δ高温超导体不可逆线与钉扎势U₀,发现该样品的不可逆线在温区72—85K范围内呈指数形式B^*-e^(-T*/T_c)函数关系,而且在温度77K,不可逆线并不能与磁测量临界电流密度J_c=0相对应,我们认为高温超导体的不可逆线的函数形式与样品的钉扎势紧密关联。 关键词：     

McMillan Tc公式的解析推导(Ⅱ)——μ*≠0情形

本文把文献[1]的理论以及所得到的T_c公式推广到μ^*≠0情形,得到T_c=(2γ)/πω_log·(ω_log/ω_c)^{(μ*/(λ-μ*))}·exp{-(1+λ)/(λ-μ^*)}. Inγ=C=0.5772是Euler常数。 关键词：     

Same-sign tetralepton signature in type-Ⅱ seesaw at lepton colliders

The same-sign tetralepton signature via the mixing of neutral Higgs bosons and their cascade decays to charged Higgs bosons is a unique signal in the type-Ⅱ seesaw model with the mass spectrum M_A⁰≈M_H⁰>M_H⁺>M_H^±±.In this study,we investigate this signature at future lepton colliders,such as the ILC,CLIC,and MuC.Direct searches for doubly charged scalar H^±±at the LHC have excluded MHg+t<350(870) GeV in the H^±±+W^±W(±)(l^±±)decay mode.Therefore,we choose M_A⁰=400,600,1000,1500 GeV as our benchmark scenarios.Constrained by direct search,H^±±+W^±W(±)(l^±±)d=is the only viable decay mode for Mρ=400 GeV at the √s=1 TeV ILC.With an integrated luminosity L=8 ab^-1,the promising region,with approximately 150 signal events,corresponds to a narrow band in the range of 10^-4 GeV≤v△≤10^-2GeV.Meanwhile,for Mpo=600 GeV at the √s=1.5 TeV CLIC,approximately 10 signal events can be produced with L=2.5 ab^-1.For heavier triplet scalars M_A⁰■870 GeV,although the H^±± decay mode is allowed,the cascade decays are suppressed.A maximum event number~16 can be obtained at approximately v△~4×10⁴GeV and λ₁₄~0.26 for M_A⁰=1000 GeV with L=5 ab^-1 at the √s=3 TeV CLIC.Finally,we find that this signature is not promising for M_A⁰= 1500 GeV at the √s=6 TeV MuC.Based on the benchmark scenarios,we also study the observability of this signature.In the H^±±+W^±W(±)(l^±±)d mode,one can probe MρS 800(1160) GeV at future lepton colliders.     

McMillan Tc公式的解析推导(Ⅲ)

本文把作者在前面两篇文章导出的T_c公式推广成下面形式:T_c=αω_log(ω_log/ω_c)^{(μ*/(λ-μ*))exp{-(1+λ)/(λ-μ*)},并从线性Eliashberg方程出发,导出了计算α的方程组。α一般是λ和μ*的函数。在弱耦合极限下,由上述方程组解得,α=2γ/π,其中lnγ=C=0.5772是Euler常数。这个结果表明了,前面两篇文章得到的T_c公式在弱耦合极限下是正确的。作者进而在Einstein谱和μ*=0情形,用数值计算方法从定α的方程组算出当λ=0.23,0.25,0.38和0.48时,a的数值。结果表明,至少在0.23≤λ≤0.45区间中,α变化很小,近似等于1/1.30。此时,本文的T_c公式实际上就是Allen及Dynes修改后的经验的McMillan T_c公式。 关键词：}     

立方磁晶各向异性对面内磁场中条畴和磁泡稳定性的影响

在八个(111)面磁泡膜上,观察了施加面内(in-plane)磁场后在不同晶轴方向上条状畴的消失过程,测量了条畴消失场H_s^*和磁畴消失场H_k^*与面内磁场的方向的关系。本文计及立方磁晶各向异性,完善了面内磁场中条畴的稳定性理论。用该理论定性地解释了实验结果的主要特点。导出了H_s^*与立方各向异性及面内场方向的两种近似的理论关系,它们分别适用于面内场方向靠近和不十分靠近〈110〉晶轴的情形。它们和实验结果是大致符合的。在〈110〉晶轴上,理论关系具有下列简单的形式:H_k^*<110>=H_s^*<110>=H_k{1+(k₁/2K_u)-[al/h(4πM_s/H_k)²]^2/3},此式与实验结果符合得相当好。 关键词：     

关于一级近似Tc级数解的收敛问题

本文通过一个实例说明:μ^*=0时,一级近似T_c级数解的收敛半径既不是由z_ph=-∫₀^(ω_ph)dωg(ω)dω·ω²/(ω_ph²-ω²),也不是由z_ph=∫₀^(ω_ph)dωg(ω)dω·ω^{2< 关键词：}     

Rb(62D)原子与基态Rb原子,H2分子碰撞转移截面

本文用荧光法测量Rb(6²D)原子与基态Rb原子,H₂分子碰撞转移截面。结果表明:Rb(6²D)-Rb(5²s)转移截面为σ_fs=67×10^-14cm²,σ_tr=4.3×10^-14cm²,Rb(6²D)—H₂转移截面为σ_fs 关键词：     

AlH分子10个Λ-S态和26个Ω态光谱性质的理论研究

在修正了各种误差(自旋-轨道耦合效应、标量相对论效应、核价相关效应及基组截断)的基础上,本文利用内收缩的多参考组态相互作用(icMRCI)+Q方法计算了AlH分子10个Λ-S态和26个Ω态的势能曲线.利用包含自旋-轨道耦合效应的icMRCI/AV6Z~*理论计算了X¹∑_((0⁺)⁺),a³Π_0⁺,a³Π₁,a³Π₂和A¹Π₁态之间的跃迁偶极矩.计算得到的光谱常数和跃迁数据与现有的实验值符合很好.研究发现:1)A¹Π₁-X¹∑_((0⁺)⁺)(0,0),(0,1),(0,2),(1,0),(1,1),(1,2),(1,3),(1,4)和(1,5)带Q(J")支的跃迁比较强,随着J"的增大,Δv=0带的爱因斯坦A系数和振...     

Vortex pinning in YBa2Cu3O7?x films

Evidence that pinning on linear or planar defects dominates the vortex dynamics in YBa₂Cu₃O_7−x (YBCO) films is provided by complex impedance measurements at temperature 8 K<T<T _c and magnetic field 0<B<6 T. Below the vortex lattice melting transition B_g(T) but above a threshold field B_p≈8(1-T/T _c ) T, the inductance of vortices increases as B², much less rapidly than predicted for collective pinning of vortices by point defects. Above the vortex melting line, critical scaling persists over the region B_g(T<B<B^*(T) where the vortex correlation length ξ exceeds a characteristic length scale ξ^*≡ξ(B=B^*)≈450?. The value of ξ^* is not sensitive to Al-doping in the Cu sites in the lattice and is close to the size of twin domains in the film. The nature of the observed crossovers is discussed in terms of available theoretical models for a glass-liquid transition at B_g.     

Vortex lattice in Bi2Sr2CaCu2O8+δ well above the first-order phase-transition boundary

Measurements of non-local in-plane resistance originating from transverse vortex-vortex correlations have been performed on a Bi₂Sr₂CaCu₂O_8+δ high-T_c superconductor in a magnetic field up to 9 T applied along the crystal c-axis. Our results demonstrate that a rigid vortex lattice does exist over a broad portion of the magnetic field-temperature (H-T) phase diagram, well above the first-order transition (FOT) boundary H_FOT(T). The results also provide evidence for the vortex lattice melting and vortex liquid decoupling phase transitions, occurring above the H_FOT(T).     

Reversible magnetization and irreversibility line of tri-layer superconductor Ba2Ca2Cu3O6(O,F)2 with Tc∼108 K

We report magnetization measurements of grain-aligned Ba₂Ca₂Cu₃O₆(O,F)₂ with T_c?108 K. The interlayer distance of the material is the shortest among known tri-layer superconductors. Unexpectedly, the magnetization data show that the coupling strength between CuO₂ layers is rather weak. A direct reflection of the weak coupling is highly suppressed irreversibility line, i.e. a broad reversible region in H-T plane. The decoupling field obtained from the irreversibility line is less than 0.1 T, which is comparable with that of quasi two-dimensional superconductor Bi₂Sr₂CaCu₂O_8+δ. Comparison of data with the Hao-Clem model gives characteristic parameters [ξ_ab(0) and λ_ab(0)] and the critical fields [H_c(0) and H_c2^c(0)]. A large value of penetration depth, λ_ab(0)=240 nm reflects a small carrier concentration in CuO₂ planes, and explains the reason of the weak interlayer coupling.     

Antiferromagnetic resonance in α-RbMnCl3 · 2H2O

Antiferromagnetic resonance results on α-RbMnCl₃ · 2H₂O below the Néel temperature 4.56 K are reported. At T = 1.2K we find for the anisotropy fields H^c = 440 Oe and H^a = 1510 Oe. The spin flop field at T = 1.2K is 14.62 kOe.     

YBa2Cu3O7-δ外延薄膜的有效钉扎势

在0—7T磁场范围内，测量了不同测量电流密度下YBa₂Cu₃O_7-δ外延薄膜的电阻温度关系.实验结果表明，临界温度以下，混合态的耗散电阻率能很好地用热激活磁通蠕动描述.有效钉扎势的电流密度关系遵守Zeldov等人提出的对数关系，有效钉扎势的温度和磁场关系遵守U∝(1-T/T_c)H^-α关系，其中α=0.63，与热激活磁通点阵位错运动模型相一致，表明样品具有2D涡旋性质. 关键词：     

Enhanced superconducting properties of Eu2O3-doped MgB2

Bulk polycrystalline samples of Eu₂O₃-doped MgB₂ have been synthesized by a standard solid state reaction route and their structural and superconducting properties have been investigated. As a function of Eu₂O₃ content we have found a significant increase in the critical current density (J_c) and the irreversibility field (H_irr) in the magnetic field range 0–6 T. The XRD results reveal the presence of MgO and EuB₆ secondary phases along with the main hexagonal phase of MgB₂. The strain values and the lattice distortions have been found to increase almost linearly with the nominal Eu₂O₃ content. The observed significant improvement in J_c(H) and H_irr in the Eu₂O₃-doped MgB₂ samples, thus is mainly attributed to the lattice distortions introduced by Eu₂O₃ doping.     

Magneto-optical studies on ferromagnetic stripe domains in K2CuF4

Ferromagnetic stripe domains are observed in K₂CuF₄ below T_c=6.19 K by use of Faraday rotation (FR). They are about 4 μm wide and lie parallel to the c-planes. They are due to a very small intraplanar anisotropy field as a result of the minute orthorhombic lattice distortion observed by Hidaka and Walker. A stripe domain model, including closure domains for complete demagnetization, is in accordance with the experimental observations if the anisotropy fields H^out_A=1.4kOe and Hⁱⁿ_A=0.1 Oe are introduced. Long-range order, presumably induced by interplanar exchange, is a accompanied by 3d Ising critical behavior as verified by critical exponents obtained from different magneto-optical measurements (α=0.07, β=0.33 and δ=4.6). Changes of the domain structure, of the ac-plane FR, and of the ac-plane linear birefringence due to a transverse magnetic field H 6 a are discussed. A non-vanishing internal field is preceded by a domain instability. The compatibility of the domain structure with neutron scattering results of Hirakawa and Yoshizawa is discussed.     

2H-Nb0.9Ta0.1Se2中磁通涡旋输运的标度行为

测量了2H-Nb_0.9Ta_0.1Se₂单晶样品在不同电流下电压随磁场变化的曲线V(H),并从V(H)曲线得到V(I)数据.使用标度关系V=α(I-I_c)^β进行了拟合,得到了临界电流随磁场I_c(H)和微分电阻随磁场R_d的变化关系.在微分电阻随磁场变化的曲线中,电流较大时,靠近上临界磁场H_c2附近出现一个强峰,而在低电流下,该峰消失.同 关键词： 磁通涡旋 标度定律 临界电流峰效应     

Doping dependence of the vortex glass and sublimation transitions in the high-T<Subscript>c</Subscript> superconductor La<Subscript>2-x</Subscript>Sr<Subscript>x</Subscript>CuO<Subscript>4</Subscript> as determined from macroscopic measurements

Magnetization and ac-susceptibility measurements are used to characterize the mixed phase of the high-temperature cuprate superconductor La_2-xSr_xCuO₄ over a large range of doping (0.075 0.20). The first order vortex lattice phase transition line H_FOT(T), the upper critical field H_c2(T) and the second peak H_sp(T) have been investigated up to high magnetic fields (8 Tesla applied perpendicular to the CuO₂ planes). Our results reveal a strong doping dependence of the magnetic phase diagram, which can mainly be explained by the increasing anisotropy with underdoping. Within our interpretation, the first order vortex lattice phase transition is due to the sublimation (rather than melting) of the vortex lattice into a gas of pancake vortices, whereas the second peak is related to the transition to a more disordered vortex glass state.