层状超导体Cu_(0.03)TaS_2中E～j特性的涡旋玻璃模型标度

在高温超导体中,涡旋玻璃理论可以很好地描述其中的涡旋玻璃相.选择合适的参数,就可以通过标度方程将磁场下混合态的E~j曲线标度到E+和E-两个分支上.但是,这个二阶相变模型对于层状超导体Cu0.03TaS2却不适用,原因为该体系中的弱钉扎,这可以从磁滞回线上的"峰效应"得到证明.     

高TC超导体的涡旋相结构与超声衰减关系研究

根据Fisher的超导涡旋玻璃相理论,提出了高温超导体混合态超声衰减的涡旋形态模型．论述了高温超导体混合态复杂的相结构,给出了各向异性高温超导体的混合态相图．概括出超声衰减两种类型：钟型(衰减较缓慢)与λ型(衰减较迅速),并且揭示相应的相结构及其特点．同时指出：在温度比超导临界温度低的情况下Pankert超声波与涡旋线相互钉扎机制较为适用,在温度较超导临界温度高的情况,涡旋线相变模型较为适用．     

二维行人交通模型中转向运动对阻塞相变的影响

采用二维元胞自动机模型研究周期边界条件下正方形网格上的行人交通现象. 与Muramatsu-Nagatani的行人模型不同,提出了两个模型采用并行更新规则. 在模型I中,研究不同系统尺寸下转向运动对于相变的影响;而在模型II中,研究不同比例的两类行人运动时的相变现象. 模拟结果显示:当行人密度超过临界密度后,就会发生动力学阻塞相变,而发生相变的临界密度显著提高. 由于行人转向运动,从自由运动相到阻塞相存在一个很宽的过渡区域,在该区域内系统可能演化到两种不同的终态.     

蒙特卡罗方法模拟无序涡旋系统中的相图

从GL(Ginzburg-Landau)自由能出发,在最低朗道能级近似下,用蒙特卡罗的方法模拟了二维无序第二类超导体涡旋态系统.对于纯净的涡旋系统,得到了从涡旋固态到涡旋液态的一级相变,验证了前人的理论.对于无序的涡旋系统,发现低温区域存在Bragg玻璃态.     

约瑟夫森结中的涡旋动力学特性

利用周期瞬子方法从理论上研究了环状偏流约瑟夫森结中的单个涡旋隧穿特性.将涡旋在约瑟夫森结中的运动简化为一个粒子在特定势阱中的运动,由于涡旋可以从阱中逃逸,这就使得涡旋在阱中的能态是不稳定的.理论上指出,正是由于涡旋的隧穿,使得涡旋所处的能态是亚稳态,该能态是一个复数,其虚部正比于能态的衰变率.通过理论计算得出:在温度较高的情况下,涡旋进行的是热隧穿,在低温条件下,涡旋的逃逸只能通过量子隧穿的方式.还指出过程中系统随着温度的降低,通过二阶转变过程从热隧穿过渡到了量子隧穿.     

关于建立涡旋引力场及“水星进动”与“岁差”运行机制的统一

依据引力场与电磁场应具有的对称性,以及引力场理论应具有的完备性,即以库仑力静电场与万有引力场的对称性,以及电流产生磁场与运动物体产生涡旋引力场的对称性,建立了涡旋引力场.将万有引力与涡旋引力对行星运动的综合作用,对水星进动和地球岁差运行机制的统一性作了论证;对静止卫星轨道摄动作了分析;对太阳系多个行星的岁差作了推算;对章动的物理意义和定义作了新的探讨;并解释了涡旋引力场与旋涡星系蝶形结构形成的关系.经对涡旋引力场理论建立及与实际结合的一致性的论证表明:运动物体将产生涡旋引力场,以万有引力和涡旋引力场组成的引力系统更符合太阳系行星运行的实际,以及本文涡旋引力场理论的建立过程及结论的合理性.并在此基础上,建立了由万有引力和涡旋引力综合作用下的行星轨道模型.     

两个纳米点接触下磁涡旋的动力学行为

研究了两个纳米点接触系统中磁涡旋的动力学行为.平面外的两个极化电流分别通过一个位于盘中心的纳米接触点和一个不在盘中心的纳米接触点通入坡莫纳米盘.随着电流密度的增加,磁涡旋依次出现了旋转回归运动、极性反转、奇异的磁涡旋构型等动力学现象.重点研究了磁涡旋旋转回归运动的轨迹和旋转频率.     

自旋极化电流驱动下磁涡旋的旋转回归运动和手征性反转

将方向为（-1,1,-1）的3个自旋极化电流通入纳米盘, 用OOMMF(object oriented micromagnetic framework）软件分析自旋极化电流大小和位置分布对磁涡旋动力学行为的影响. 结果表明： 磁涡旋核做旋转回归运动时, 最大速度在轨迹上的位置相对固定, 利用该性质， 可在最大速度处引入缺陷, 使磁涡旋核运动到缺陷处被钉扎并发生反转, 从而实现磁涡旋核极性的可控反转； 通过改变极化电流的大小或位置, 可调节磁涡旋核旋转回归运动频率的大小； 在高电流密度区域, 可实现磁涡旋手征性反转, 且反转时间较短； 与极化电流位置对称分布相比, 其手征性反转的电流范围变大, 达到暂态构型的时间变短.      

自旋极化电流驱动下磁涡旋的旋转回归运动和手征性反转

将方向为（-1,1,-1）的3个自旋极化电流通入纳米盘, 用OOMMF(object oriented micromagnetic framework）软件分析自旋极化电流大小和位置分布对磁涡旋动力学行为的影响. 结果表明： 磁涡旋核做旋转回归运动时, 最大速度在轨迹上的位置相对固定, 利用该性质， 可在最大速度处引入缺陷, 使磁涡旋核运动到缺陷处被钉扎并发生反转, 从而实现磁涡旋核极性的可控反转； 通过改变极化电流的大小或位置, 可调节磁涡旋核旋转回归运动频率的大小； 在高电流密度区域, 可实现磁涡旋手征性反转, 且反转时间较短； 与极化电流位置对称分布相比, 其手征性反转的电流范围变大, 达到暂态构型的时间变短.      

`Pd40Ni10Cu20P20块状金属玻璃的高压相变

利用日本同步辐射装置研究了高温高压下Pd₄₀Ni₁₀Cu₂₀P₂₀ 块状金属玻璃的非晶-晶化转变. 在10 GPa的压力条件下加热该金属玻璃, 实时观察到了非晶-晶化-非晶的相变规律. 在7 GPa 和同样的温度条件下, Pd₄₀Ni₁₀Cu₂₀P₂₀金属玻璃仅存在非晶-晶化这样不可逆相变. 将该金属玻璃在7 GPa的压力条件下加热到熔化温度, 然后淬火到室温, 发现淬火后获得的晶化相与加热金属玻璃得到的 晶化相完全不同. 表明该金属玻璃在不同的压力条件下存在着不同的晶化机制.     

A Bragg glass phase in the vortex lattice of a type II superconductor

Although crystals are usually quite stable, they are sensitive to a disordered environment: even an infinitesimal amount of impurities can lead to the destruction of crystalline order. The resulting state of matter has been a long-standing puzzle. Until recently it was believed to be an amorphous state in which the crystal would break into 'crystallites'. But a different theory predicts the existence of a novel phase of matter: the so-called Bragg glass, which is a glass and yet nearly as ordered as a perfect crystal. The 'lattice' of vortices that contain magnetic flux in type II superconductors provide a good system to investigate these ideas. Here we show that neutron-diffraction data of the vortex lattice provides unambiguous evidence for a weak, power-law decay of the crystalline order characteristic of a Bragg glass. The theory also predicts accurately the electrical transport properties of superconductors; it naturally explains the observed phase transitions and the dramatic jumps in the critical current associated with the melting of the Bragg glass. Moreover, the model explains experiments as diverse as X-ray scattering in disordered liquid crystals and the conductivity of electronic crystals.     

Dynamic instabilities and memory effects in vortex matter

The magnetic flux line lattice in type II superconductors serves as a useful system in which to study condensed matter flow, as its dynamic properties are tunable. Recent studies have shown a number of puzzling phenomena associated with vortex motion, including: low-frequency noise and slow voltage oscillations; a history-dependent dynamic response, and memory of the direction, amplitude duration and frequency of the previously applied current; high vortex mobility for alternating current, but no apparent vortex motion for direct currents; and strong suppression of an a.c. response by small d.c. bias. Taken together, these phenomena are incompatible with current understanding of vortex dynamics. Here we report a generic mechanism that accounts for these observations. Our model, which is derived from investigations of the current distribution across single crystals of NbSe2, is based on a competition between the injection of a disordered vortex phase at the sample edges, and the dynamic annealing of this metastable disorder by the transport current. For an alternating current, only narrow regions near the edges are in the disordered phase, while for d.c. bias, most of the sample is in the disordered phase--preventing vortex motion because of more efficient pinning. The resulting spatial dependence of the disordered vortex system serves as an active memory of the previous history.     

匀动螺旋单涡管诱导压力场的解析解

推导了在圆柱直管中作均匀运动的螺旋单涡管诱导核外压力场的解析表达式,若令柱管直径趋于无穷大,该表达式也能够描述在无限域中螺旋单涡管诱导核外压力场,假设相对速度场定常且具有螺旋对称性,并利用已获得的涡管诱导相对速度场和相对坐标系下动量方程求其诱导压力场,获得的结果显示：压力场是时间的周期函数,仅当螺旋涡管静止或沿自身的空间螺旋线轴滑移时,螺旋涡诱导的压力场退化为定常场,该退化现象已被实验证实;圆柱直管壁上的压力极值点计算位置与现有实验的测量位置一致,压力公式显示管壁压力脉动频率是均匀分布的,这一结论也与现有压力实验的频域特性相符合。     

两相流中颗粒相对湍流动能修正的模型及其应用

讨论了两相流中颗粒相对湍流动能及其耗散率的影响．通过单个颗粒在流场中运动的分析,推导出由颗粒引起的湍流动能的耗散,并和由颗粒后的尾流及涡的脱落引起的湍流动能的增加一起加入ｋε方程中,将此模型应用到竖直圆管中的气粒两相流的计算, 并与实验结果进行比较,发现本文的模型比文献［１］ 的模型有一定的改进．     

Clarifying the glass-transition behaviour of water by comparison with hyperquenched inorganic glasses

The formation of glasses is normal for substances that remain liquid over a wide temperature range (the 'good glassformers') and can be induced for most liquids if cooling is fast enough to bypass crystallization. During reheating but still below the melting point, good glassformers exhibit glass transitions as they abruptly transform into supercooled liquids, whereas other substances transform directly from the glassy to the crystalline state. Whether water exhibits a glass transition before crystallization has been much debated over five decades. For the last 20 years, the existence of a glass transition at 136 K (ref. 3) has been widely accepted, but the transition exhibits qualities difficult to reconcile with our current knowledge of glass transitions. Here we report detailed calorimetric characterizations of hyperquenched inorganic glasses that, when heated, do not crystallize before reaching their glass transition temperatures. We compare our results to the behaviour of glassy water and find that small endothermic effects, such as the one attributed to the glass transition of water, are only a 'shadow' of the real glass transition occurring at higher temperatures, thus substantiating the conclusion that the glass transition of water cannot be probed directly.     

Mesoscopic superconductor as a ballistic quantum switch.

Several key experiments have revealed a rich variety of vortex structures in mesoscopic superconductors in which only a few quanta of magnetic flux are trapped: these structures are polygon-like vortex 'molecules' and multi-quanta giant vortices. Ginzburg-Landau calculations confirmed second-order phase transitions between the giant vortex states and stable molecule-like configurations. Here we study theoretically the electronic structure and the related phase-coherent transport properties of such mesoscopic superconductor systems. The quasiparticle excitations in the vortices form coherent quantum-mechanical states that offer the possibility of controlling the phase-coherent transport through the sample by changing the number of trapped flux quanta and their configuration. The sample conductance measured in the direction of the applied magnetic field is determined by the transparency of multi-vortex configurations, which form a set of quantum channels. The transmission coefficient for each channel is controlled by multiple Andreev reflections within the vortex cores and at the sample edge. These interference phenomena result in a stepwise behaviour of the conductance as a function of the applied magnetic field, and we propose to exploit this effect to realize a vortex-based quantum switch where the magnetic field plays the role of the gate voltage.