量子尺寸效应对超薄Pb(111)薄膜性质的影响

讨论了超薄Pb(111)薄膜在构型和稳定性方面的量子机制.首先对量子尺寸效应和电子生长以及薄膜稳定性的判断标准作了介绍,然后以Pb(111)薄膜作为例子,介绍了其生长的特性和强烈的量子尺寸效应,最后阐述了量子尺寸效应对薄膜的物理和化学性质具有深刻影响.     

铅超薄膜在砷化镓衬底上生长量子尺寸效应研究

用基于密度泛函理论的第一性原理计算方法研究了Pb(111)超薄膜在GaAs(111)极性衬底表面上的生长过程中所表现的量子尺寸效应.研究了包括Ga截断和As截断的两种情况.研究结果发现薄膜体系的表面能、功函数和晶格驰豫随着Pb(111)超薄膜的厚度变化出现了强烈的双层振荡现象.和自由铅薄膜比较,其转折点的位置和周期的大小随着衬底及极性的不同有所变化,说明衬底电子遗漏可以在调控铅薄膜生长方面具有重要的作用.     

载流子捕获-逃逸过程对量子点激光器性能的影响

为了研究了载流子驰豫时间和逃逸时间对量子点激光器的阈值电流、外微分量子效率的影响,分析了载流子在S-K自组织量子点激光器结构中捕获、逃逸过程,建立速率方程并在稳态下求解.结果表明,驰豫时间越长,量子点基态载流子数量越少,转换为光子的数量就越少,量子点激光器的阈值电流就越大,外微分量子效率就越小;而载流子从量子点基态的逃逸到盖层的时间越长,量子点激光器的阈值电流就越小,外微分量子效率就越大.     

La0.7Sr0.3MnO3外延膜厚度引起的电阻率变化

不同厚度的La0.7Sr0.3MnO3(LSMO)外延薄膜被沉积到立方相的LaA lO3(001)单晶衬底上,XRD测试结果显示,LSMO外延膜的结构是单相的,具有与衬底相同的晶格取向;随着膜厚的增加,LSMO外延膜的晶格经历应变到驰豫的变化.电阻测量显示,应变驰豫的薄膜(较厚的薄膜)有较大的电阻率,这与该膜中缺陷浓度增加有关.此外,也对生长在不同单晶衬底上的LSMO外延膜(厚度相同)的结构和电阻进行了对比研究.     

凝聚态物质驰豫：分维时间模型

本文提出凝聚态物质驰豫的一个简单的分维时间模型，理论研究表明，凝聚态物质内的反常驰豫是由于绝热近似遭破坏的结果，且需要引入三个不同时间标度描述间断驰豫过程替代连续驰豫过程．本文提出模型不仅能很自然给出持续指数型驰豫ｅｘｐ［－（ｔ／τ）β］，而且能解释实验中观测到β的标度行为．     

偶氮聚合物薄膜的全光极化特性及其驰豫过程研究

利用旋涂法制备了一种偶氮类化合物掺杂有机聚合物薄膜,并对其吸收谱、厚度、折射率、进行了测量,采用二次谐波产生的方法的方法对全光极化后薄膜的二阶非线性光学特性进行了研究.实验结果表明,随着薄膜厚度和生色团含量的增加其二阶非线性增强.这与聚合物薄膜中含有较高浓度的分散红1有关.对极化饱和后的驰豫情况进行了分析,发现不同厚度薄膜的驰豫速度不同.这是由于薄膜中偶氮分子含量越多,分子间相互作用越强,导致驰豫时间增长.     

存在驰豫效应时表面生长的重整化群研究

用重整化群方法分析了存在表面驰豫效应时表面生长的动力学行为，得到了相应的标度指数ｘ与ｚ、驰豫时间τ的函数关系，结果表明，随着驰豫效应的增强，会使生长表面有化并有利于稳定生长阶段的形成。     

原子团簇吸附/掺杂转角双层石墨烯的量子反常霍尔效应实验研究

<正>我校物理电子工程学院孙海斌博士2018年获批国家自然科学基金面上项目:原子团簇吸附/掺杂转角双层石墨烯的量子反常霍尔效应实验研究,项目编号:11874317.量子反常霍尔效应是当前凝聚态物理和材料物理领域的一大研究热点,它不依赖于强磁场而由材料本身的自发磁化产生,能够极大地克服摩尔定律的极限,     

PVDF长时间压电弛豫的研究

研究经拉伸及极化处理的PVDF薄膜在室温附近的压电驰豫效应,发现在施力状态下及撤力后的自由状态下样品释放的电荷均遵守自由驰豫规律,考虑到PVDF与铁电陶瓷空间电荷分布的相似性,以及结晶高聚物的多相性,上述现象可以解释。     

铁电——驻极体复合材料的传导性和热电驰豫效应

研究了未极化的0—3模式、不同体积比的 TGS—PVDF 复合膜0℃至75℃的传导性和极化后的复合膜在0℃和30℃下的热电驰豫效应。发现复合膜中 TGS 与 PVDF 的耦合对复合膜的传导性和热电驰豫有影响,体积比约1∶1时影响较显著。复合膜的热电驰豫遵从 t~(1/2)规律,是空间电荷的驰豫效应。复合膜中耦合相实质上是组成复合材料的两相物质界面附近被束缚的局域空间电荷效应。     

Kondo effect in quantum dots and molecular devices

Kondo effect is a very important many-body phenomenon in condensed mailer physics, which explains why the resistance increases as the temperature is lowered （usually 〈10 K） in dilute magnetic alloy, and why the conductance increases as temperature is decreased in quantum dots. This paper simply introduces equilihrium and nonequilibrium Kondo effects in quantum dots together with the Kondo effect in quantum dots with even number of electrons （when the singlet and triplet states are degenerate）. Furthermore, Kondn effect in single aton/molecular transistorss is introduced, which indicates a new way in study Kondo effect.     

玻色-爱因斯坦凝聚体量子模拟实验技术进展

玻色爱因斯坦凝聚体（BEC）的最初理论在1925年由爱因斯坦和玻色提出,直到1994年才通过激光冷却原子气体的方法在实验室实现,并于2001年获得诺贝尔物理学奖。BEC具有宏观量子特性并且具有较长的相干时间,因此是开展量子模拟研究的重要平台。随着光阱、光晶格、微结构光阱和量子气体显微镜等技术的发展,基于BEC的量子模拟器不仅能够用于研究凝聚态物理中已有的基本模型,而且能够探索自然界中不存在的新奇量子物理现象和量子物态。甚至在非平衡和动力学演化研究方面,BEC量子模拟器可以用来研究当前物理实验中无法观测的快速量子物理现象。     

纳米材料的应用

纳米材料由于其特征的结构层次具有表面效应。小尺寸效应，量子尺寸效应。宏观量子隧道效应等特性，使拥有了一系列新颖的物理和化学特征，在众多研究领域中具有非常重要的应用价值。文中结合自己的工作对纳米材料的发展及应用进行了综述。     

Two-dimensional gas of massless Dirac fermions in graphene

Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schr?dinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.     

原子分子体系的引力效应

寻找完整的量子引力理论是目前理论物理中的前沿热点问题之一,而黑洞热力学和量子干涉仪探测引力效应被认为是正在形成的量子引力理论的两个重要的"实验区".前者通过将量子概念引入到广义相对论来检验二者如何结合,特别是量子力学幺正性将在这两个理论的结合中经受严峻考验;而后者通过量子系统在引力场背景中的演化来试验引力对系统量子属性的影响,在这一方面广义相对论等效原理在微观粒子领域将接受越来越严格的实验检验.目前,原子分子物理实验中出现了类似黑洞辐射的现象,然而,这些现象出现的理论机制还不是非常明确,究竟能否用目前已有的理论解释,或者还是需要构建新的理论来解释也是不清楚的,但是无论如何,这些现象的出现为实验研究量子引力理论打开了一扇窗户.另一方面,人们已经使用量子系统测量一些弱引力效应,这不仅为研究引力对量子系统的影响提供了便利条件,也为研究二者结合提供了一个好的突破口.本综述将结合我们近几年的工作,围绕原子分子体系中的强引力和弱引力效应来介绍和讨论这些问题.     

拓扑绝缘体与低维超导体的电输运特性

拓扑绝缘体这种具有新奇量子特性的物质和具有百余年研究历史的超导体都是当前凝聚态物理学领域的研究热点．本文简要介绍了拓扑绝缘体、超导体的研究背景和基本特性,重点回顾了拓扑绝缘体、超导薄膜及纳米桥、超导纳米线以及纳米尺度下拓扑绝缘体．超导异质结构的电输运特性．并对该领域的进一步发展做出了展望．     

Spontaneous symmetry breaking in a quenched ferromagnetic spinor Bose-Einstein condensate

A central goal in condensed matter and modern atomic physics is the exploration of quantum phases of matter--in particular, how the universal characteristics of zero-temperature quantum phase transitions differ from those established for thermal phase transitions at non-zero temperature. Compared to conventional condensed matter systems, atomic gases provide a unique opportunity to explore quantum dynamics far from equilibrium. For example, gaseous spinor Bose-Einstein condensates (whose atoms have non-zero internal angular momentum) are quantum fluids that simultaneously realize superfluidity and magnetism, both of which are associated with symmetry breaking. Here we explore spontaneous symmetry breaking in 87Rb spinor condensates, rapidly quenched across a quantum phase transition to a ferromagnetic state. We observe the formation of spin textures, ferromagnetic domains and domain walls, and demonstrate phase-sensitive in situ detection of spin vortices. The latter are topological defects resulting from the symmetry breaking, containing non-zero spin current but no net mass current.     

金属薄膜中的杂质散射效应

考虑到杂质散射效应，运用量子统计的方法，计算金属薄膜中杂质散射的弛豫时间和电导率．计算结果表明：这些物理量都是金属薄膜厚度的函数，具有量子尺寸效应．     

Light-cone-like spreading of correlations in a quantum many-body system

In relativistic quantum field theory, information propagation is bounded by the speed of light. No such limit exists in the non-relativistic case, although in real physical systems, short-range interactions may be expected to restrict the propagation of information to finite velocities. The question of how fast correlations can spread in quantum many-body systems has been long studied. The existence of a maximal velocity, known as the Lieb-Robinson bound, has been shown theoretically to exist in several interacting many-body systems (for example, spins on a lattice)--such systems can be regarded as exhibiting an effective light cone that bounds the propagation speed of correlations. The existence of such a 'speed of light' has profound implications for condensed matter physics and quantum information, but has not been observed experimentally. Here we report the time-resolved detection of propagating correlations in an interacting quantum many-body system. By quenching a one-dimensional quantum gas in an optical lattice, we reveal how quasiparticle pairs transport correlations with a finite velocity across the system, resulting in an effective light cone for the quantum dynamics. Our results open perspectives for understanding the relaxation of closed quantum systems far from equilibrium, and for engineering the efficient quantum channels necessary for fast quantum computations.     

任意空间维倾斜狄拉克费米子的带内纵向光电导的推导

狄拉克费米子是当前凝聚态物理中的研究热点.狄拉克费米子的纵向光电导，因其能够提取能带结构信息而被广泛关注.本文基于低能有效模型与线性响应理论，利用生成函数方法，解析地处理零温下任意空间维、任意倾斜相的狄拉克费米子的带内纵向光电导.特别地，我们讨论了二维和三维空间情况，并揭示了不同维度的倾斜类型对带内纵向光电导的影响.文中发展的生成函数方法有望用于其他相关问题的研究.