离子型声子晶体的光学性质

提出了离子型声子晶体的概念,发展了相应的理论：在实验上证实了离子型声子晶体中存在超晶格振动与电磁波的强烈耦合,观察到原先存在于离子晶体中的极化激元等长波光波行为;预言了一些可能的物理效应,离子型声子晶体超晶格振动和电磁波的耦合方程与黄昆方程在形式上完全一致,说明了超晶格与实际晶格在物理上的相似性。     

磁性硅烯超晶格中电场调制的谷极化和自旋极化

研究了基于硅烯的静电势超晶格、铁磁超晶格、反铁磁超晶格中谷极化、自旋极化以及赝自旋极化的输运性质,分析了铁磁交换场、反铁磁交换场以及化学势对输运性质的影响,讨论了电场对谷极化、自旋极化以及赝自旋极化的调控作用.结果表明:当3种超晶格的晶格数达到10以上时,在硅烯超晶格中很容易实现100%的谷极化、自旋极化和赝自旋极化,而且通过调节超晶格上的外加电场可以使极化方向发生翻转,从而在硅烯超晶格中实现外电场对谷自由度、自旋自由度以及赝自旋自由度的操控.     

压电效应及其在家电中的应用

 压电效应及其理论解释1880年法国物理学家皮埃尔和雅各居里兄弟在实验中发现:当某些晶体受到机械力而发生拉伸或压缩时,晶体相对的两个表面会出现等量的异号电荷。科学家把这种现象叫做压电现象,具有压电现象的介质称为压电体。当压电体发生机械形变时,其极化强度发生变化,导致表面吸附的自由电荷随之而变。如果将两个表面装上电极并用导线接通,变化的自由电荷便从一个极板移至另一极板,形成电流。如果压电体上加交变电场,则压电体就会交替出现伸长和压缩,即发生机械振动。压电效应的解释:在离子性的晶体中,正、负离子有规则地交错配置,构成结晶点阵。     

无铅四方相钙钛矿短周期超晶格压电效应机理研究

超晶格压电行为与内部正离子之间的内在联系尚缺乏相关的研究.本文基于密度泛函理论的第一性原理方法,研究了三种无铅四方相钙钛矿铁电超晶格(BaTiO_3/SrTiO_3,KNbO_3/KTaO_3和BaTiO_3/KNbO_3)中A,B位正离子对整体的极化和压电贡献.通过计算超晶格不同轴向应变条件下原子结构和Born有效电荷,获得了超晶格和各个正离子的极化值和压电系数.结果表明,在轴向压缩应变条件下(-0.15—0 A),无铅超晶格中的正离子位移D(A)和D(B)受到抑制,在拉应变时位移才显著增大,因此极化和压电行为不明显.在轴向拉伸应变作用下(0—0.15 A),无铅超晶格中各原子的极化贡献显著增大,特别是B位原子Ti,Nb和Ta的极化贡献使得总的极化强度也显著提高,并当拉应变达到一定值,超晶格才会出现明显的压电行为.无铅超晶格的极化和压电行为主要由B位正离子贡献.     

准周期铁电光学超晶格多波长二次谐波的产生

准周期材料的研究是凝聚态物理学的热门课题之一。我们利用外电场室温极化技术，成功地制备了准周期ＬｉＴａＯ３超晶格，首次获得了高效，多波长的二次谐波输出。对应的基波波长分别为０．９７６２，１．０８４６，１．８３４，１．３６５０和１．５６９９μｍ。     

应力作用下铁电超晶格BaTiO3/SrTiO3的结构和极化的第一性原理研究

通过第一性原理计算，研究了在不同应力作用下铁电超晶格BaTiO₃/SrTiO₃的结构以及自发极化的变化.结果显示，在应力作用下，晶格发生变形，并且沿着c轴在Ti原子和O原子之间电荷发生传输.随着应力的增加，超晶格中各类原子沿着c轴的位移都会有不同程度上的增加，造成了铁电超晶格的自发极化不断提高.此外，在该模型中，通过变化所施加的应力，可以控制超晶格的极化性质.     

铁电层厚度对(BiCoO_3)_n/(La_(2/3)Sr_(1/3)MnO_3)_1超晶格磁电性质的影响

本文利用第一性原理,对由四方相BiCoO_3(BCO)和La_(2/3)Sr_(1/3)MnO_3(LSMO)所构造的超晶格的形成能、电子结构与磁电性质进行了系统研究.研究表明,超晶格中BCO层厚度变化可对超晶格的电子结构,及其极化位移与自旋极化率等磁电性质产生重要影响.特别的,在BiO/Mn_BO_2为界面构型的超晶格中,当BCO侧为一个单胞层时,超晶格表现出半金属性,可获得100%自旋极化率.上述研究结果对于新型自旋电子器件研究具有一定科学意义.     

应力作用下铁电超晶格BaTiO3/SrTiO3的结构和极化的第一性原理研究

通过第一性原理计算,研究了在不同应力作用下铁电超晶格BaTiO3/SrTiO3的结构以及自发极化的变化.结果显示,在应力作用下,晶格发生变形,并且沿着c轴在Ti原子和O原子之间电荷发生传输.随着应力的增加,超晶格中各类原子沿着c轴的位移都会有不同程度上的增加,造成了铁电超晶格的自发极化不断提高.此外,在该模型中,通过变化所施加的应力,可以控制超晶格的极化性质.     

半导体超晶格系统中的磁电调控电子自旋输运研究

通过采用转移矩阵方法求解自旋电子隧穿过程,理论研究了半导体超晶格系统中电子自旋输运的磁电调控行为.结果表明：仅对超晶格系统施以磁调制,隧穿系数将出现自旋分裂,随磁场增强,电导自旋极化率变大且展宽于费米能区;若选取不变磁场情况,同时施以间隔周期电场调制,超晶格的电子极化率将有更为显著地提高.进一步发现,随电场强度的改变,电子自旋输运行为显然存在两个明显不同区域,下自旋电子将在不同调制区域表现为不同的变化趋势.然而,若对周期磁超晶格施加间隔两周期的电调制,自旋电导输运的临界行为消失,电导极化率在高能区的共振峰 关键词： 半导体超晶格 自旋输运 磁电调控     

两耦合半无限超晶格中的局域界面声子-极化激元

采用转移矩阵方法，研究了含结构缺陷层的两耦合半无限超晶格(GaAs/AlAs)中的局域界面声子-极化激元模性质. 研究发现，含不同介电特性的缺陷超晶格结构中的局域界面声子-极化激元模在剩余射线区［ω_TO, ω_LO］的分布情况与数量存在不同，而且反对称模表现出不同的特征. 文中着重研究了缺陷层介电常数与角频率无关的缺陷超晶格，发现该结构中的局域界面声子-极化激元模对组分层的排列顺序与厚度、缺陷层的厚度以及横向波数有着不同程度的依赖.     

New type of polariton in a piezoelectric superlattice

We studied the propagation of an electromagnetic (EM) wave in a piezoelectric superlattice. Because of the piezoelectric effect, a transverse polarization can be induced by a longitudinal wave which couples strongly to the EM wave in some particular frequency regions, resulting in the creation of a new type of polariton that does not exist in ionic crystals. The forbidden band associated with the polariton is not due to the Bragg reflection, but rather to the coupling.     

Theory of nonlinear excitation of surface polaritons in lossy media

The purpose of this paper is to study the nonlinear excitation of surface polaritons taking fully into account the damping of the active medium and the finite cross-section of the nonlinear polarization on the interface. This problem is solved using the guided wave calculation techniques where the EM field at the surface polariton frequency is expanded over a complete set of normal modes of the unperturbed interface. Using a “table method” we find that this set includes one guided mode, which is the surface polariton mode, and two classes of radiation modes. The expressions of all these modes are derived and interpreted physically. We then get the expression of the EM field excited at the surface polariton frequency inside and outside the pumped region and show that, in the general case, it is a mixture of all these normal modes. The end of the paper is mainly devoted to the study of the surface term occurring in the expression of the EM field at the surface polariton frequency: we point out the existence of a resonance phenomenon with two kinds of surface polariton modes: the “spatial” one and the “temporal” one. The corresponding dispersion curves, or resonance curves, are given and it is explained how each of them can be obtained experimentally.     

Shear Bloch waves and coupled phonon–polariton in periodic piezoelectric waveguides

Coupled electro-elastic SH waves propagating in a periodic piezoelectric finite-width waveguide are considered in the framework of the full system of Maxwell’s electrodynamic equations. We investigate Bloch–Floquet waves under homogeneous or alternating boundary conditions for the elastic and electromagnetic fields along the guide walls. Zero frequency stop bands, trapped modes as well as some anomalous features due to piezoelectricity are identified. For mixed boundary conditions, by modulating the ratio of the length of the unit cell to the width of the waveguide, the minimum widths of the stop bands can be moved to the middle of the Brillouin zone. The dispersion equation has been investigated also for phonon–polariton band gaps. It is shown that for waveguides at acoustic frequencies, acousto-optic coupling gives rise to polariton behavior at wavelengths much larger than the length of the unit cell but at optical frequencies polariton resonance occurs at wavelengths comparable with the period of the waveguide.     

Terahertz phonon polariton imaging

In this article, we primarily review the time-resolved imaging of THz phonon polariton, which is generated by femtosecond laser in ferroelectric crystal. We pay more attention to the imaging in thin crystal, which can be used as an integration platform for terahertz-optics or terahertz-electrics. The imaging techniques, which can get quantitatively in-focus time-resolved images, are introduced in more detail. They have made enormous progress in recent years, and are powerful tools for the research of phonon polariton, optics, and THz wave. We also briefly introduce the generation principle and general propagation properties of THz phonon polariton.     

Phonon-polariton in two-dimensional piezoelectric phononic crystals

The phonon-polariton behaviors of two-dimensional piezoelectric phononic crystals (PPCs) were studied using the plane wave expansion method. The governing equations combine Maxwell's equations and Newton's equations of motion. A mode-repulsion can be formed by strong coupling between electromagnetic (EM) waves and elastic waves in the vicinity of the center of the first Brillouin zone for PPC that comprises piezoelectric material and with opposite polarization in different periodically organized areas. Take a 2D ZnO PPC as a numerical example, it was decoupled into two independent groups. One refers to the mixed mode of the in-plane elastic waves and the transverse-magnetic (TM) mode EM waves. The other group refers to the mixed mode of the out-of-plane elastic waves and the transverse-electric (TE) mode EM waves. Coupling repulsion is also observed in these two groups.     

Piezoelectric-induced polariton coupling in a superlattice

Propagation of electromagnetic waves in a piezoelectric superlattice is studied. Because of the piezoelectric effect, a coupling between two orthogonally polarized electromagnetic waves is induced by the superlattice vibration. As a consequence of the strong coupling, two types of polariton modes are found: one is supported in the band gap while the other prohibited. This unusual coupling effect is not present in classical lattices.     

Phonon-polariton and band structure of electro-magneto-acoustic SH wave propagation oblique to the periodic layered piezoelectric structures

Electro-magneto-acoustic SH waves propagating oblique to the periodic layered piezoelectric structures are studied under the coupling of the acoustic wave and the electromagnetic wave. Band structures of the so-called piezoelectric superlattice and phononic/photonic crystal are given both at acoustic frequencies and at optical frequencies. For the periodic layered piezoelectric structures, phonon-polaritons (the coupling modes of the phonons and photons) are found not only happening near the center of the Brillouin zone (in the long-wavelength limit) at acoustic frequencies, but also being able to appear in the whole Brillouin zone at optical frequencies. Appearing of these phonon-polaritons may provide a way to design a new type of acousto-optic devices.     

极化激元(polaritons)与拉曼散射

在给出介质中的光（电磁）波与极化波混合作用而得出的极化激元方程。极化激元色散方程之后又讨论了相应的物理意义及相关的物理问题；获得极化激元的实验方法。接着还介绍和讨论了极化激元的拉曼散射。     

光量子阱单滤波、多通道开关

在对称的光学厚度为1/4波长光子晶体体系中插入另一光学厚度为半波长的光子晶体形成光量子阱.通过控制入射光强可微小地改变此含缺陷光子晶体材料的介电常数,从而可形成高效的多通道光学开关,同时位于中心频率处的EM波保持高透射.研究表明该光学开关的阈值随缺陷光子晶体的层数增加而减小.