关键词： coherent   quantum   utilize  

摘要： We propose a scheme for controlling the coherent transport of a single electron through a closed three-level structure in coupled quantum *** coherent transport is externally controlled by applying a weak few-cycle pulse with an adjustable carrier-envelope phase(CEP).It is revealed numerically that there exists a significant dependence of the electron transport on the *** results illustrate the potential to utilize few-cycle pulses for the excitation in coupled quantum dot systems through control of the CEP,as well providing guidance in the design for possible experimental implementations.

关键词： CdS quantum dot   TiO2 nanowire   QD-SSC   Photovoltaic performance   Photoelectron transport property  

摘要： Single-crystalline rutile TiO2 nanowires were synthesized in situ on transparent conductive oxide (TCO) glass substrate and CdS quantum dots (QDs) were deposited on nanowires to form a TiO2/CdS heterojunction structure. The orientation growth, single-crystalline structure of TiO2 nanowire and the core-shell structure of TiO2/CdS were confirmed by XRD, SAED and HR-TEM measurements. The QD sensitized solar cells (QD-SSCs) were assembled and the optical, photoelectrical properties of QD-SSCs were investigated. The results showed that CdS QDs enhanced the optical absorbance of TiO2 in the visible region, therefore greatly improved the photovoltaic performance of solar cells. Under optimum parameters, a power conversion efficiency of 1.72% was achieved. Electron impedance spectroscopy measurement was also carried out to investigate the kinetics of charge transfer and recombination in QD-SSCs. The effects of amount of QDs and photoelectron transport properties of QD-SSCs on the cell efficiency were analyzed. It was proved that the amount of QDs was more important factor than electron lifetime and transfer rate for cell efficiency when the coverage of QDs on TiO2 was not high enough.

关键词： 单负特异材料   量子阱   多通道滤波  

摘要： 研究了由电单负特异材料量子阱实现的可调紧凑型多通道滤波器。利用电磁场传输矩阵方法计算出由两层电单负特异材料和一层正常介电材料构成的单个量子阱,及多个级联量子阱实现的可调型多通道滤波性。电单负特异材料的介电常数由德鲁得模型给出。通过多个电单负特异材料量子阱的耦合使得单个共振峰被劈裂成多个分离的共振峰导致了多通道滤波特性。跟常规的多通道滤波器比较,本文设计的滤波器结构更紧凑,而且可调节性好,有望在未来的光子器件中发挥作用。

关键词： 宽禁带半导体   输运   自旋  

摘要： Ⅲ族氮化物半导体具有宽的直接带隙,很强的极化电场,优异的物理特性,是发展高频、高温、高功率电子器件和光电子器件的优选材料.同时,Ⅲ族氮化物半导体有很长的电子自旋弛豫时间以及很高的居里温度,也成为近年来半导体自旋电子学研究的重要材料体系之一.本文介绍了用量子输运和自旋光电流方法对GaN基异质结构中载流子的量子输运和自旋性质的研究进展.对Ⅲ族氮化物半导体中的能带结构,子带占据和散射,自旋分裂及自旋轨道耦合机制等进行了讨论.

关键词： Coherent systems   Gas lasers   High resolution spectroscopy   Laser sources   Terahertz spectroscopy   Ultrafast lasers  

摘要： The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser. (c) 2013 Optical Society of America

关键词： 科学中心   北京大学   材料   量子   创新   科研机构  

摘要： 量子材料科学中心是北京大学（简称北大）成立的理工医领域“新体制科研机构”之一。这个中心从一诞生起，便以“创新”为使命。

关键词： MAGNONS   COMPOSITE materials   THERMOPHYSICAL properties   BRILLOUIN scattering   MAGNETITE   NANOPARTICLES  

摘要： We describe the preparation of multilayer composite coating comprising nanoparticles of magnetite on metal substrates previously modified by sonication. Using the Brillouin light-scattering method, we have investigated the spectral characteristics of thermal magnons in these films as a function of the number of layers and the external magnetic-field strength.

关键词： QUANTUM theory   QUANTUM phase transitions   NONEQUILIBRIUM statistical mechanics   KONDO effect   NONEQUILIBRIUM flow   KOSTERLITZ-Thouless transitions  

摘要： The resonant-level model represents a paradigmatic quantum system which serves as a basis for many other quantum impurity models. We provide a comprehensive analysis of the nonequilibrium transport near a quantum phase transition in a spinless dissipative resonant-level model, extending earlier work [Phys. Rev. Lett 102, 216803 (2009)]. A detailed derivation of a rigorous mapping of our system onto an effective Kondo model is presented. A controlled energy-dependent renormalization-group approach is applied to compute the nonequilibrium current in the presence of a finite bias voltage V. In the linear-response regime V→0, the system exhibits as a function of the dissipative strength a localized-delocalized quantum transition of the Kosterlitz-Thouless (KT) type. We address fundamental issues of the nonequilibrium transport near the quantum phase transition: Does the bias voltage play the same role as temperature to smear out the transition? What is the scaling of the nonequilibrium conductance near the transition? At finite temperatures, we show that the conductance follows the equilibrium scaling for VT. We furthermore provide different signatures of the transition in the finite-frequency current noise and ac conductance via a recently developed functional renormalization group (FRG) approach. The generalization of our analysis to nonequilibrium transport through a resonant level coupled to two chiral Luttinger liquid leads, generated by fractional quantum Hall edge states, is discussed. Our work on the dissipative resonant level has direct relevance to experiments on a quantum dot coupled to a resistive environment, such as H. Mebrahtu et al., [Nature (London) 488, 61 (2012)].

关键词： APPROXIMATION theory   GREEN'S functions   DIFFERENTIAL equations   QUANTUM theory   RESEARCH   POTENTIAL theory (Mathematics)  

摘要： In this work, the low rank approximation concept is extended to the non-equilibrium Green's function (NEGF) method to achieve a very efficient approximated algorithm for coherent and incoherent electron transport. This new method is applied to inelastic transport in various semiconductor nanodevices. Detailed benchmarks with exact NEGF solutions show (1) a very good agreement between approximated and exact NEGF results, (2) a significant reduction of the required memory, and (3) a large reduction of the computational time (a factor of speed up as high as 150 times is observed). A non-recursive solution of the inelastic NEGF transport equations of a 1000 nm long resistor on standard hardware illustrates nicely the capability of this new method. (C) 2013 AIP Publishing LLC.

关键词： 铁磁体   自旋极化输运   自旋极化率   隧穿系数   Rashba自旋轨道相互作用  

摘要： 根据量子相干输运理论,利用传递矩阵的方法,研究自旋电子在铁磁体(F)/半导体多量子阱(SWM)/铁磁体的一维结构中,考虑自旋轨道耦合效应时的量子相干输运的特性.通过计算发现在这种一维多量子阱结构中的自旋电子的输运特性发生了一定的变化,这有利于进一步提高自旋电子的隧穿系数和自旋极化率.