Effects of Depolarization Field and Interfacial Coupling on the Polarization of Ferroelectric Bilayers

A ferroelectric bilayer model considering depolarization field and interfacial coupling is proposed and the expression of the depolarization field is derived. The spatial profiles of spontaneous polarization and hysteresis loops are calculated using the numerical method with and without considering the depolarization field. The effects of the depolarization field and interfacial coupling on the polarization of second-order ferroelectric bilayers are studied systematically. When interfacial coupling is ferroelectric coupling, the interface spontaneous polarization increases and the area of hysteresis loop becomes larger with increasing coupling. When interfacial coupling is antiferroelectric coupling, the depolarization field makes the central loop become smaller and the shape of the hysteresis loop becomes steep. Meanwhile, as interfacial coupling increases, the outer loops stretch further out horizontally and the size of the central loop widens.     

P(VDF-TrFE)铁电聚合物薄膜不对称铁电开关现象

报道了铁电聚合物薄膜中观测到的不对称铁电开关双峰现象．当薄膜被略低于其矫顽场的电场极化时可观测到铁电开关双峰,当进一步连续施加超过矫顽场的电场后这一开关双峰现象消失．用空间电荷的注入和再分布模型对这一不对称现象进行了探讨．     

Correlation between Imprint and Long-Time Polarization Reversal under Low Fields in Ferroelectric Thin Films

Time interval of slow polarization reversal in ferroelectric thin films is broadened over more than two decades to disobey the classical Kolmogorov-A vrami-Ishibashi （KAI） equation as the applied field approaches the coercive field of domain switching. The assumption of a Lorentzian distribution of logarithmic waiting times of reversed domain nucleation in this equation can resolve this dilemma. In our work, we explain this equation from the coercive-voltage distribution in thin films, and derive a similar function to describe slow polarization reversal from the consideration of a long-time imprint effect rather than the KAI model.     

二维随机介质中偏振模式的竞争和阈值特性

基于随机激光的时域理论,建立了横磁与横电光波模式共享反转粒子数情况下的理论模型,并利用时域有限差分法(FDTD)数值求解麦克斯韦方程组和速率方程组,从而获得了二维随机介质内横磁与横电光波模式的阈值特性.结果表明,如果横磁与横电偏振模式之间没有共享反转粒子数,则横磁光波模式拥有较低的激发阈值;反之,则横电光波模式的激发阈值更低.在共享反转粒子数的情况下,改变样品的表面填充率对两种偏振模式的阈值并没有很大的影响,而增加样品面积则可以明显的降低横磁模式的阈值.     

Methods for Switching Radiation Polarization in GaAs Laser Diodes

Technical Physics - Operation modes of laser structures with controlled polarization of light have been studied and the results of measuring polarization characteristics are presented. The...     

Effective Pyroelectric Coefficient and Polarization Offset of Compositionally Step-like Graded Ferroelectric Structures

In this paper, the effective pyroelectric coefficient and polarization offset of the compositionally step-like graded multilayer ferroelectric structures have been studied by use of the first-principles approach. It is exhibited that the dielectric gradient has a nontrivial influence on the effective pyroelectric coefficient, but has a little influence on the polarization offset; and the polarization gradient plays an important role in the abnormal hysteresis loop phenomenon of the compositionally step-like graded ferroelectric structures. Moreover, the origin of the polarization offset is explored, which can be attributed to the polarization gradient in the compositionally step-like graded structure.     

制备全光功能开关的多量子阱材料设计

采用有效质量框架下一维有限深势阱模型对InGaAsP多量子阱的组分和阱宽之间的关系进行了计算,利用更符合实验结果的Harrison模型来计算带阶,分别就晶格匹配和应变补偿两种情况进行了比较计算,最后根据要制作的全光功能开关的性能指标对计算结果进行了选择,得到最适合于制作光开关的材料.     

Carbon Nanotubes in Arrays: Competition of van-der-Waals and Elastic Forces

Doklady Physics - The van-der-Waals interaction between carbon nanotubes leads to the formation of agglomerates of bundles and strands. In such a self-assemblage, identical nanotubes are assembled...     

Polarization Switching Bistability and Dynamics in Vertical-Cavity Surface-Emitting Laser under Orthogonal Optical Injection

Bistability as well as dynamics associated to polarization switching in a vertical-cavity surface-emitting laser (VCSEL) submitted to orthogonal optical injection from an external master laser are investigated. Intensity-polarization switching bistability is studied by increasing and decreasing the intensity of the injected beam and for a fixed frequency detuning, i.e. the frequency offset between master and the free running VCSEL. Depending on the frequency detuning, bistable switching is experimentally found to occur with or without injection locking of the fundamental mode to the master laser frequency. For large positive detuning, injection locking of the first-order transverse mode with a strong depression of the fundamental mode has been observed. The case of frequency – polarization switching bistability, i.e. when the frequency detuning is first decreased and then increased for a fixed injected power, has also been theoretically analyzed. Qualitative comparison with previous experimental work is presented for the dependence of the width of the bistable switching region on the injection strength level. Finally we show an experimental result of complicated dynamics including period doubling route to chaos that accompany polarization switching and which motivates future theoretical investigations.     

原位Raman光谱技术应用于铁电陶瓷畴变与电疲劳研究

基于铁电陶瓷材料90°畴变导致Raman光谱变化的原理,自行设计并搭建了铁电材料原位测试分析和数据采集系统,通过与Raman光谱仪的联用,利用特制的样品旋转装置,从实验上证实在外加电场作用下铁电材料中的90°畴变使平均电畴的择优取向发生改变,从而导致Raman光谱强度的变化,利用铁电材料原位测试分析和数据采集系统,实现...     

Evidence of the Ferroelectric Polarization in Charge Transport through WTe2 Weyl Semimetal Surface

JETP Letters - We investigate electron transport along the surface of WTe2 three-dimensional single crystals, which are characterized by the coexistence of the conductivity and ferroelectricity of...     

AlGaN合金中局域态和极化电场的竞争机制

通过MOVPE方法生长了不同Al组分的3块Al_xGa_1-xN样品,利用稳态光谱和时间分辨光谱对其样品的光学特性进行了分析。鉴于影响氮化物发光性质的极化电场或局域态的单一机制不能充分解释我们的实验现象,提出了局域态-内部极化电场竞争的机制。通过对实验数据的分析,得出如下重要结论：样品PL峰位蓝移的温度起点基本对应于局域态和极化电场起作用的交替点,PL峰位发生蓝移的温度起点与光强-温度曲线的斜率出现明显变化的温度点一致;随着温度的升高,若AlGaN合金样品中PL峰位存在二次蓝移,则说明样品中电场分布不均匀。     

Core Polarization and Tensor Coupling Effects on Magnetic Moments of Hypernuclei

Effects of core polarization and tensor coupling on the magnetic moments in ¹³_ΛC, ¹⁷_Λ, and ⁴¹_ΛCa Λ-hypernuclei are studied by employing the Dirac equation with scalar, vector and tensor potentials. It is found that the effect of core polarization on the magnetic moments is suppressed by Λ tensor coupling. The Λ tensor potential reduces the spin--orbit splitting of p_Λ states considerably. However, almost the same magnetic moments are obtained using the hyperon wavefunction obtained via the Dirac equation either with or without the Λ tensor potential in the electromagnetic current vertex. The deviations of magnetic moments for p_Λ states from the Schmidt values are found to increase with nuclear mass number.     

基于InGaAs/InP多量子阱的全光偏振开关的研究

研究了一种基于InGaAs/InP多量子阱的全光偏振开关,讨论了相空间填充(PSF)效应引起的激子饱和以及光学非线性,计算了在抽运光下的阱中载流子布居数随时间的变化,推导出了探测光偏振态的主轴瞬态旋转角.计算结果表明,在100 pJ飞秒脉冲抽运下该全光开关理论旋转角最大可达60°.     

Chirality and correlations in graphene

Graphene is described at low energy by a massless Dirac equation whose eigenstates have definite chirality. We show that the tendency of Coulomb interactions in lightly doped graphene to favor states with larger net chirality leads to suppressed spin and charge susceptibilities. Our conclusions are based on an evaluation of graphene's exchange and random-phase-approximation correlation energies. The suppression is a consequence of the quasiparticle chirality switch which enhances quasiparticle velocities near the Dirac point.     

Quantum Limits of Polarization Switching in Optical Mesoscopic Devices with Distributively Coupled Quantum Modes

The quantum theory of nonlinear dynamics and the switching effect for two distributively coupled modes in optical systems has been developed based on the Hartree approximation. The quantum limits for observation of the switching effect for the polarization characteristics of light has been determined. The creation of a new type of nonclassical mesoscopic states of light like the Schrödinger-cat states and mesoscopic qubit/qutrit states is predicted. The theoretical prediction is confirmed by a numerical estimation of real systems, i.e., tunnel-coupled optical fibers and waveguides, for the experimental realization of the states under consideration.     

Competition between ferroelasticity and ferroelectricity

In the crystals of the KH₂PO₄ family, the properties of ferroelasticity and ferroelectricity strongly interact. It is for example possible to change by application of an electric field the orientation of the phase front between high temperature and low temperature phases, and to observe the rotation of reticular planes during an electric hysteresis cycle drawing. These phenomena, as the existence of a quasi constant domain width illustrate the particular competition between ferroelasticity and ferroelectricity in these compounds.     

Competition between neutrino and gravitational radiation

This essay discusses the competition between neutrino radiation and gravitational radiation for the dominant method by which forming neutron stars radiate away their gravitational collapse energy. It is shown that neutrinos may, in fact, be the dominant mode; thus a failure to detect gravitation radiation from a supernova does not imply an error in general relativity but rather the existence of a more efficient radiation mechanism.This essay was awarded the third prize for 1976 by the Gravity Research Foundation.