Gapless Chiral Superconducting ( d + id )-Wave Phase in Strongly Correlated Layered Material with a Triangular Lattice

It is shown that interlayer electron tunneling in the quasi-two-dimensional ensemble of Hubbard fermions leads to the realization of the gapless superconducting phase with the chiral (d + id)-wave order parameter symmetry, not for a single value of sodium ion concentration, but in a wide range of concentrations. Precisely this situation corresponds to experimental data on the layered sodium cobaltite intercalated by water (NaxCoO2 ⋅ yH2O). Intra-atomic electron repulsion that determines the strong electron correlation regime leads to the representation of Hubbard fermions, the interaction of which ensures Cooper instability. Intersite intralayer interactions between fermions considerably affect the positions of nodal points of the chiral order parameter and change the critical concentration at which a topological transition occurs in the 2D system of Hubbard fermions.     

Cumulant t-Expansion for Strongly Correlated Electrons on a Lattice

Journal of Experimental and Theoretical Physics - A systematic nonperturbative scheme for calculating the ground state energy is adapted for studying systems of strongly correlated electrons on a...     

高压下 MgB2 超导的涡旋动力学研究*

我们首次通过磁弛豫的方法系统研究了高压下 MgB2 样品的磁通钉扎以及涡旋动力学, 测量了其在不同温度和磁场下的磁化强度 M 随时间t 的衰变, 即 M(t) . 根据集体蠕动理论, 明确了高压效应在低磁场时抑制了磁衰变速率, 但在高场下大大的加快了磁衰变. 高压降低了临界电流密度J c 和钉扎能. 另外, 在 MgB2 样品里低场下没有观测到弹性蠕变向塑性蠕变的转变.     

Giant Vortex States in a Long Superconducting Cylinder with a Hole in Center

We have theoretically studied the nucleation of superconductivity in doubly connected superconductors in the form of long superconducting cylinders. The giant vortex states are investigated with the nonlinear Ginzburg-Landau theory. The solutions of Ginzburg-Landau equations are solved numerically with relaxation method. The quantum size effect is clearly shown through the calculation of free energy.     

Two-Dimensional Coulomb Glass as a Model for Vortex Pinning in Superconducting Films

A glass model of vortex pinning in highly disordered thin superconducting films in magnetic fields B ≪ H_c2 at low temperatures is proposed. Strong collective pinning of a vortex system realized in disordered superconductors that are close to the quantum phase transition to the insulating phase, such as InO_x, NbN, TiN, MoGe, and nanogranular aluminum, is considered theoretically for the first time. Utilizing the replica trick developed for the spin glass theory, we demonstrate that such vortex system is in non-ergodic state of glass type with a large kinetic inductance per square L_K. The distribution function of local pinning energies is calculated, and it is shown that it possesses a wide gap; i.e., the probability to find a weakly pinned vortex is extremely low.

     

Lattice Boltzmann Study of a Vortex Ring Impacting Spheroidal Particles

Interaction of vortex rings with solid is an important research topic of hydrodynamic. In this study, a multiple-relaxation time (MRT) lattice Boltzmann method (LBM) is used to investigate the flow of a vortex ring impacting spheroidal particles. The MRT-LBM is validated through the cases of vortex ring impacting a flat wall. The vortex evolution due to particle size, the aspect ratio of a prolate particle, as well as Reynolds $(Re)$ number are discussed in detail. When the vortex ring impacting a stationary sphere, the primary and secondary vortex rings wrap around each other, which is different from the situation of the vortex ring impacting a plate. For the vortex ring impacting with a prolate spheroid, the secondary vortex ring stretches mainly along the long axis of the ellipsoid particle. However, it is found that after the vortex wrapping stage, the primary vortex recovers along the short axis of the particle faster than that in the long axis, i.e., the primary vortex ring stretches mainly along the short axis of the particle. That has never been addressed in the literature.     

Longitudinal Dust Lattice Shock Wave in a Strongly Coupled Complex Dusty Plasma

The effect of hydrodynamical damping that arises due to the irreversible processes within the system have been studied on 1D nonlinear longitudinal dust lattice wave (LDLW) in homogeneous strongly coupled complex (dusty) plasma. Analytical investigation shows that the nonlinear wave is governed by Korteweg‐de Vries Burgers' equation. This hydrodynamical damping induced dissipative effect is responsible for the Burgers' term that causes the generation of shock wave in dusty plasma crystal. Numerical investigation on the basis of the glow‐discharge plasma parameters reveal that LDLW exhibits both oscillatory and monotonic shock. The shock is compressive in nature and its strength decreases (increases) with the increase of the shielding parameter κ (characteristic length L). The effects of dust‐neutral collision are also discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于铅铟合金线的SFQ多芯片超导互连方法研究

用基于铅铟合金线的引线键合(WB)工艺对单磁通量子(SFQ)多芯片的超导互连方法进行了研究,将铅含量75%,铟含量25%的铅铟合金线制备成WB线材,用超声楔形焊工艺成功实现SFQ芯片I/O接口焊盘的超导互连.拉力测试表明室温下铅铟合金线键合强度与同线径金线相当,优于同线径铝线;用开尔文四端法测量了铅铟合金线互连的多级超导转变温度以及线材与超导芯片之间的接触电阻,结果表明该铅铟合金线的超导转变温度为6.63 K,当温度降低至6.63 K或更低时,铅铟合金线的线阻以及线材与SFQ芯片I/O接口焊盘的接触电阻为0,实现了超导互连;并通过热冲击实验验证该WB结构具有优异的热稳定性.     

Effect of Lattice Quantum Fluctuation on CDW of MX Solids

The reduction of charge density wave (CDW) amplitude of MX solids caused by the lattice quantum fluctuation is investigated in a wide range of electron-phonon coupling by using the self-consistent renormalization method. In contrast to polyacetylene, where the bond order wave (BOW) exists well in arbitrary coupling, the effect of the quantum Auctuatipn on CDW of MX solids distinctly depends on the coupling. When the coupling is strol; the reduction of CDW is small; but, if the coupling is weak, CDW is seriously suppressed and even nearly destroyed. This contrast is related to the fact that for weak coupling, the renormalized frequencies of both the acoustic and optical branches are greatly reduced in polyacetylene, but these frequencies in MX solids are not well different from the bare value ω₀.     

无限细光束中透射起伏时间相关频谱法高浓度效应的模拟

时间或空间相关透射起伏频谱法是近年发展起来的一种新的颗粒测量方法,它可同时测量颗粒粒径分布和浓度,并可用来进行在线、实时测量。研究表明,随着浓度增大,逐渐增强的高浓度效应会导致测量值越来越严重地偏离理论值。本文采用模拟计算方法讨论无限细光束照射下的时间相关透射起伏频谱法高浓度效应并给出部分实验验证。分析表明,无限细光束照射时的透射起伏相关频谱主要受到层结构效应的影响,颗粒交叠效应不明显,表明为随着颗粒浓度增大,转换函数(特征函数)逐渐偏离低浓度理论值并向无因次相关时间小的方向移动,阶高始终保持不变。     

基于非线性涡格法的快速静气动弹性数值模拟技术

基于2.5D RANS数据和VLM耦合的方式,发展了一种考虑非线性流动效应的混合型涡格法HVLM.采用矩形直/后掠机翼两个外形的跨声速算例,通过与VLM、三维CFD计算数据的比较,对HVLM的气动力预测精度进行了分析与评估.对比结果表明,HVLM在大幅降低时间成本的前提下可以获得和三维CFD方法预测值十分接近的计算数据,对线化VLM方法的修正效果显著.然后,HVLM与悬臂梁有限元求解耦合,实现了一种面向三维机翼的快速静气动弹性数值模拟技术,并通过矩形直机翼算例进行了验证.耦合算例的时间分析数据表明,HVLM/Beam耦合的方式能够在10 s以内完成1次三维机翼静气动弹性分析,在气动/结构耦合分析、优化设计方面展示出了良好的应用前景.      

Spontaneous Formation of Antiferromagnetic Vortex Lattice in a Fast Rotating BEC with Dipole Interactions

When a Bose-Einstein condensate is set to rotate,superfluid vortices will be formed,which finally condense into a vortex lattice as the rotation frequency further increases.We show that the dipole-dipole interactions renormalize the short-range interaction strength and result in a distinction between interactions of parallel-polarized atoms and interactions of antiparallel-polarized atoms.This effect may lead to a spontaneous breakdown of the rapidly rotating Bose condensate into a novel anti-ferromagnetic-like vortex lattice.The upward-polarized Bose condensate forms a vortex lattice,which is staggered against a downward-polarized vortex lattice.A phase diagram related to the coupling strength is obtained.     

Nonequilibrium Green Functions Approach to Strongly Correlated Fermions in Lattice Systems

Quantum dynamics in strongly correlated systems are of high current interest in many fields including dense plasmas, nuclear matter and condensed matter and ultracold atoms. An important model case are fermions in lattice systems that is well suited to analyze, in detail, a variety of electronic and magnetic properties of strongly correlated solids. Such systems have recently been reproduced with fermionic atoms in optical lattices which allow for a very accurate experimental analysis of the dynamics and of transport processes such as diffusion. The theoretical analysis of such systems far from equilibrium is very challenging since quantum and spin effects as well as correlations have to be treated non‐perturbatively. The only accurate method that has been successful so far are density matrix renormalization group (DMRG) simulations. However, these simulations are presently limited to one‐dimensional (1D) systems and short times. Extension of quantum dynamics simulations to two and three dimensions is commonly viewed as one of the major challenges in this field. Recently we have reported a breakthrough in this area [N. Schlünzen et al., Phys. Rev. B (2016)] where we were able to simulate the expansion dynamics of strongly correlated fermions in a Hubbard lattice following a quench of the confinement potential in 1D, 2D and 3D. The results not only exhibited excellent agreement with the experimental data but, in addition, revealed new features of the short‐time dynamics where correlations and entanglement are being build up. The method used in this work are nonequilibrium Green functions (NEGF) which are found to be very powerful in the treatment of fermionic lattice systems filling the gap presently left open by DMRG in 2D and 3D. In this paper we present a detailed introduction in the NEGF approach and its application to inhomogeneous Hubbard clusters. In detail we discuss the proper strong coupling approximation which is given by T ‐matrix selfenergies that sum up two‐particle scattering processes to infinite order. The efficient numerical implemen‐tation of the method is discussed in detail as it has allowed us to achieve dramatic performance gains. This has been the basis for the treatment of more than 100 particles over large time intervals. The numerical results presented in this paper concentrate on the diffusion in 1D to 3D lattices. We find that the expansion dynamics consist of three different phases that are linked with the build‐up of correlations. In the long time limit, a universal scaling with the particle number is revealed. By extrapolating the expansion velocities to the macroscopic limit, the obtained results show excellent agreement with recent experiments on ultracold fermions in optical lattices. Moreover we present results for the site‐resolved behavior of correlations and entanglement that can be directly compared with experiments using the recently developed atomic microscope technique. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

在金属基片上激光沉积YBCO超导薄膜

介绍了在金属基片上激光沉积缓冲层和ＹＢａ２Ｃｕ３ｏ７－ｘ（ＹＢＣＯ）高温超导薄膜的研究结果。在带ｙｔｔｒｉａ－ｓｔａｂｉｌｉｚｅｄ－ｚｉｒｃｏｎｉａ（ＹＳＺ）缓冲层的ＮｉＣｒ合金基片上,激光原位沉积出ＹＢＣＯ超导薄膜,薄膜的零电阻转变温度度４８Ｋ,７７Ｋ时临界电流密度约为２００Ａ／ｃｍ＾２;缓冲层的取向可以通过选择适当的沉积参数来改善;用扫描隧道电子显微镜对ＹＢＣＯ薄膜的微观结构分析表明：完善的螺     

强非局域介质中基于古依相位的旋转涡旋光孤子

利用强非局域非线性介质中傍轴光束传输的修正Snyder-Mitchell模型讨论了两束共线(即光束中心和传输方向都相同)拉盖尔-高斯型光孤子(CLGS)构成的涡旋光孤子传输过程。在一定条件下,涡旋光束在传输过程中,光束截面光斑发生旋转现象,但光束的束宽保持不变,称之为旋转涡旋光孤子。涡旋光孤子旋转的现象可以通过叠加光场中的古依相位来解释。结果展现了几个旋转涡旋光孤子在传输过程中的旋转现象和强非局域介质中多环形旋转涡旋光孤子的传输。