Superconductivity in electron-doped arsenene

Based on the first-principles density functional theory electronic structure calculation,we investigate the possible phonon-mediated superconductivity in arsenene,a two-dimensional buckled arsenic atomic sheet,under electron doping.We find that the strong superconducting pairing interaction results mainly from the pz-like electrons of arsenic atoms and the A1 phonon mode around the K point,and the superconducting transition temperature can be as high as 30.8 K in the arsenene with 0.2 doped electrons per unit cell and 12%-applied biaxial tensile strain.This transition temperature is about ten times higher than that in the bulk arsenic under high pressure.It is also the highest transition temperature that is predicted for electron-doped two-dimensional elemental superconductors,including graphene,silicene,phosphorene,and borophene.     

插层三元铁硒超导体的电子结构和磁性质的理论研究

最近发现的插层三元铁硒超导体AyFexSe2（A=K,Rb,Cs和/或Tl）显示诸多新颖现象.为了澄清这些现象,作者分别计算了没有铁空位的基于完整四方FeSe层的AFe2Se2,含有四分之一铁空位的4×2或2×2超结构的AFe1.5Se2,以及含有五分之一铁空位的槡5×槡5超结构的A0.8Fe1.6Se2三种情况下的电子结构和相应的磁构型,发现AFe2Se2是双共线反铁磁的半金属,而AFe1.5Se2和A0.8Fe1.6Se2则是分别具有数十和数百毫电子伏特能隙的反铁磁半导体,并分别处于共线反铁磁长程序和区块化棋盘反铁磁长程序中.作者还分析和讨论了AyFexSe2的这些基本电子结构可能对超导性质的影响.     

耦合量子阱中激子凝聚的研究进展

近年来，半导体量子阱中激子的玻色一爱因斯坦凝聚研究取得了很大进展．实验上利用耦合量子阱间接激子中电子和空穴在空间上的分离，显著提高了激子的冷却速度和寿命，成功地把激子冷却到1K以下，观察到了激子的准凝聚状态，并且在强激光照射下，发现了随光照强度增强而增大的激子发光环和环上形成的有规则斑点图案，引起了广泛的兴趣和重视．理论研究表明，发光环的出现是电子和空穴在量子阱中的反常输运行为造成的，但环上形成规则斑点的物理机理目前尚不清楚．文章介绍了这方面的实验背景和形成激子环的物理图像，指出了理论研究中存在的问题，并对解决问题的方案进行了讨论．     

Generalized Lanczos method for systematic optimization of tensor network states

We propose a generalized Lanczos method to generate the many-body basis states of quantum lattice models using tensor-network states(TNS). The ground-state wave function is represented as a linear superposition composed from a set of TNS generated by Lanczos iteration. This method improves significantly the accuracy of the tensor-network algorithm and provides an effective way to enlarge the maximal bond dimension of TNS. The ground state such obtained contains significantly more entanglement than each individual TNS, reproducing correctly the logarithmic size dependence of the entanglement entropy in a critical system. The method can be generalized to non-Hamiltonian systems and to the calculation of low-lying excited states, dynamical correlation functions, and other physical properties of strongly correlated systems.     

强关联物理研讨会简讯

20 0 1年 1月 8日至 12日中国高等科学技术中心和中国科学院理论物理研究所联合举办了“强关联物理”研讨会 .参加者逾 5 0人 .研讨会邀请了在美国工作的张世伟和斯其苗教授、香港科技大学的吴大琪教授、以及国内的一批活跃在科研一线的年轻人作专题报告 .会议共安排报告 2 4个 .研讨会对高温超导、量子反铁磁材料等强关联体系中的一些前沿实验与理论物理问题进行了深入的研究和讨论 .在理论研究方面 ,香港科技大学吴大琪教授报告了他在磁性超导体方面做的工作 ;美国Ｒｉｃｅ大学斯其苗教授介绍了国际上在量子临界现象研究方面的新进展 ;来…     

Electronic structures of ternary iron arsenides A Fe 2 As 2 ( A = Ba,Ca, or Sr)

We have studied the electronic and magnetic structures of the ternary iron arsenides AFe₂As₂ (A = Ba, Ca, or Sr) using the first-principles density functional theory. The ground states of these compounds are in a collinear antiferromagnetic order, resulting from the interplay between the nearest and the next-nearest neighbor superexchange antiferromagnetic interactions bridged by As 4p orbitals. The correction from the spin–orbit interaction to the electronic band structure is given. The pressure can reduce dramatically the magnetic moment and diminish the collinear antiferromagnetic order. Based on the calculations, we propose that the low energy dynamics of these materials can be described effectively by a t−J_H−J₁−J₂-type model [arXiv: 0806.3526v2, 2008].     

Effect of Impurity on the Doping-Induced in-Gap States in a Mott Insulator

Motivated by the recent measurements of the spatial distribution of single particle excitation states in a hole-doped Mott insulator,we study the effects of impurity on the in-gap states,induced by the doped holes,in the Hubbard model on the square lattice by the cluster perturbation theory.We find that a repulsive impurity potential can move the in-gap state from the lower Hubbard band towards the upper Hubbard band,providing a good account for the experimental observation.The distribution of t...     

Electronic structures of ternary iron arsenides <Emphasis Type="Italic">A</Emphasis>Fe<Subscript>2</Subscript>As<Subscript>2</Subscript> (<Emphasis Type="Italic">A</Emphasis> = Ba,Ca, or Sr)

We have studied the electronic and magnetic structures of the ternary iron arsenides AFe₂As₂ (A = Ba, Ca, or Sr) using the first-principles density functional theory. The ground states of these compounds are in a collinear antiferromagnetic order, resulting from the interplay between the nearest and the next-nearest neighbor superexchange antiferromagnetic interactions bridged by As 4p orbitals. The correction from the spin-orbit interaction to the electronic band structure is given. The pressure can reduce dramatically the magnetic moment and diminish the collinear antiferromagnetic order. Based on the calculations, we propose that the low energy dynamics of these materials can be described effectively by a t-J _H -J ₁-J ₂-type model [2008, arXiv: 0806.3526v2].     

双寡头垄断结构下的技术授权及社会福利分析——基于内生技术创新的视角

在具有水平差异且进行古诺竞争的双寡头结构中考虑技术拥有企业内生决定降低成本技术的创新程度,分析不同授权方式下技术拥有者利润、消费者剩余以及社会总福利的变化,并对不同授权方式下的技术创新程度进行比较。研究表明:技术拥有者通过双重收费、特许权收费方式总能实现利润增加,且双重收费方式能带来最大利润,而固定收费方式可能降低其利润;固定收费方式下消费者剩余、社会总福利高于双重收费,更高于特许权收费方式;技术创新程度与技术授权方式以及产品替代程度有关,且无论产品的替代程度如何,双重收费方式下的技术创新程度达到最大。     

Translation invariant tensor product states in a finite lattice system

We show that the matrix (or more generally tensor) product states in a finite translation invariant system can be accurately constructed from a same set of local matrices (or tensors) that are determined from an infinite lattice system in one or higher dimensions. This provides an efficient approach for studying translation invariant tensor product states in finite lattice systems. Two methods are introduced to determine the size-independent local tensors.