Spin-polarized transport in all-metal mesoscopic spin-valve devices

In spintronic devices the spin of the electron as well as its charge is utilized. We have fabricated a spin-valve device consisting of two permalloy electrodes which are connected by a normal-metal strip made of aluminum. By changing the relative alignment of the magnetizations of the electrodes the resistance of the device can be controlled. The domain configurations of the electrodes are imaged by magnetic-force microscopy in external fields at room temperature. In transport measurements at temperatures between 1.8 and 150 K we identify the observed magnetoresistance as a spin-valve effect.     

Modeling rectification effects in mesoscopic superconducting devices

We study thermal fluctuations and capacitive effects on small Josephson Junction Rings (JJR) that mimics the rectification phenomena recently observed in triangular shaped mesoscopic superconductors, due to the superposition of the field induced persistent current with the bias current. At finite temperature we predicted that the amplitude of the rectified signal depends strongly on the current contacts configuration on the JJR, in coincidence with experiments. In addition, we analyze the range of parameters where a closed loop of capacitive junctions is an appropriate model to explain the experimental observations. We conclude that the closed loop of weak links, a JJR, is a simple, robust and good model to explain the observed voltage rectification effects on mesoscopic superconducting samples for a wide range of temperature.     

Stadium型介观器件腔中粒子逃逸率的研究

本文研究了粒子在二维弱开口的Bunimovich Stadium型介观混沌器件中的逃逸规律.利用经典统计的方法,通过改变器件端口宽度、圆弧半径及器件腔长等参数,首次发现随器件各项参数变化的分形维数与粒子逃逸率趋势符合,并揭示了混沌体系的逃逸指数受器件形状的影响.统计并拟合了粒子逃逸率与粒子波数大小的关系,数值结果表明,粒子逃逸率与波数为二次函数关系,但逃逸率与能量大小不是严格的线性关系.进一步分析了在器件入口处粒子的衍射效应对粒子逃逸的影响,结果表明,衍射效应使粒子逃逸率增加,且粒子数的演化在时间较短时不再满足指数关系,长时间的演化再次满足指数衰减规律.     

Spin-orbit coupling and spin current in mesoscopic devices

Recently,the spin-orbit coupling and spin current in nanodevice have been investigated extensively.In this paper,we review the recent progresses in this field.We introduce the real space Hamiltonian and the second quantization Hamiltonian of a typical quantum transport mesoscopic device,metal-QD-metal configuration,containing the spin-orbit interaction,e-e interactions,and magnetic field.Some noteworthy effects(e.g.,the spin-polarized current,spin accumulation,persistent spin current) originated from the spin-orbit interaction are reviewed,and the electric field induced by spin-current is mentioned.Lastly,we introduce some unsolved problems and prospects in this field.     

Interaction of mesoscopic Josephson devices with non-classical microwaves

Mesoscopic Josephson devices, interacting with non-classical microwaves, are studied. The phase difference in Josephson's equations is a quantum mechanical operator, whose expectation value with respect to the density matrix describing the microwaves, determines the current. Dual phenomena with vortex condensates in Josephson array insulators are also considered. Dual Josephson junctions for vortices, made from two insulators separated by a weak link through which the vortices tunnel, are described by dual Josephson equations.     

Anisotropic magnetoresistance and spin-valve effect in all-metal mesoscopic spin-valve devices

We have fabricated all-metal lateral spin-valve devices consisting of two permalloy electrodes and an interconnecting aluminum strip. The micromagnetic behavior of the device has been imaged with a magnetic-force microscope in external magnetic fields at room temperature. During a single cooling cycle at temperatures between 2 and 120 K we have measured the anisotropic magnetoresistance of both electrodes and the magnetoresistance of the entire device. In the latter, we can clearly identify the contributions of the anisotropic magnetoresistance and the mesoscopic spin-valve effect.     

Effect of dephasing on the current statistics of mesoscopic devices

We investigate the effects of dephasing on the current statistics of mesoscopic conductors with a recently developed statistical model, focusing, in particular, on mesoscopic cavities and Aharonov-Bohm rings. For such devices, we analyze the influence of an arbitrary degree of decoherence on the cumulants of the current. We recover known results for the limiting cases of fully coherent and totally incoherent transport and are able to obtain detailed information on the intermediate regime of partial coherence for a varying number of open channels. We show that dephasing affects the average current, shot noise, and higher order cumulants in a quantitatively and qualitatively similar way, and that consequently shot noise or higher order cumulants of the current do not provide information on decoherence additional or complementary to what can be already obtained from the average current.     

Electronic transport time through mesoscopic devices with contact barriers

Information about the transport time of electrons through a quasi one-dimensional sample is obtained by calculating the energy auto-correlation function of the conductance. Depending on the length of the sample and its coupling to the external device (here modelled by perfectly conducting leads), the transport time undergoes a smooth crossover between two different limiting regimes. In the case of long samples and good coupling it coincides with the diffusion time. In the opposite limit of short and weakly coupled systems, however, the transport time is given by the reciprocal of the quantum mechanical decay width into the leads. The transition between both regimes is discussed in terms of a few model independent concepts.     

相干输运中的接点问题

为了研究介观体系的相干输运中接点的重要作用,采用一简单的纳米单势垒“二维-一维-二维”(2D-1D-2D)模型,应用散射矩阵方法和托马斯-费米近似,计算了体系透射率和在直流电压下电势分布. 结果表明： 1)接点对其透射率有显著的影响; 2)电势降落表现的电导性质违背了与经典串联电路中等价的基尔霍夫定律. 因此介观体系中各器件与接点间是量子相干的,考虑接点问题有利于对介观体系相干输运更为深入的研究. 关键词： 相干输运 接点 介观体系     

Role of mesoscopic morphology in charge transport of doped polyaniline

In doped polyaniline (PANI), the charge transport properties are determined by mesoscopic morphology, which in turn is controlled by the molecular recognition interactions among polymer chain, dopant and solvent, Molecular recognition plays a significant role in chain conformation and charge delocalization. The resistivity of PANI doped by camphor sulfonic acid (CSA)/2-acrylo-amido-1-propane sulfonic acid (AMPSA)/dodecyl benzene sulfonic acid (DBSA) is around 0.02 Ω cm. PANI-CSA and PANI-AMPSA show a metallic positive temperature coefficient of resistivity above 150 K. with a finite value of conductivity at 1.4 K; whereas, PANI-DBSA shows hopping transport at low temperatures. The magnetoresistance is positive (negative) for PANI-CSA (PANI-AMPSA); and PANI-DBSA has a large positive MR. The behavior of MR suggests subtle variations in mesoscopic morphology between PANI-CSA and PANI-AMPSA.     

Nanoscale dynamical mean-field theory for molecules and mesoscopic devices in the strong-correlation regime

We develop a nanoscale dynamical mean-field theory (nano-DMFT) to deal with strong Coulomb interaction effects in physical systems that are intermediate in size between atoms and bulk materials, taking into account the tunneling into nearby electrodes. Focusing on a simplified treelike geometry, the usual DMFT loop simply stops when the finite lattice is fully covered, starting with an initial seed provided by the electronic environment at the boundary. To illustrate this nano-DMFT, we investigate the disappearance of the quasiparticle weight in a correlated nano object near the Mott transition. In contrast to thermally driven classical phase transitions, quantum effects lead to unexpected oscillations of the order parameter, related to the interference of coherent renormalized quasiparticles. This behavior also implies a spatially inhomogeneous Mott localization process at the nanoscale.     

Schottky contacts in germanium nanowire network devices synthesized from nickel seeds

This paper presents reliable process to the synthesis of germanium nanowires by the vapor–liquid–solid method using nickel as an alternative catalyst to gold, the most commonly used metal, without toxic gas precursors. The structural study showed single-crystalline germanium nanowires with diamond structure, lengths of tens of microns and diameters smaller than 40 nm. The reduced dimensions of the nanowires led to phonons localization effect, with correlation lengths of the same order of the nanowires diameters. Additionally, the analysis of electronic properties of metal-nanowire-metal devices indicated the presence of Schottky barriers, whose values depend linearly on temperature. This linear dependence was assigned to the tunneling process through an insulator layer (mostly GeO_x) at the metal-semiconductor interface. These results point to the existence of another channel for electrons transference from metal to semiconductor being very significant to electronic devices fabrication.     

RIKEN介观器件腔中粒子输运过程的混沌性质及分形自相似结构研究

研究了粒子在RIKEN介观器件中的输运性质, RIKEN器件的理论模型是二维Sinai台球的一种, 是研究粒子逃逸曲线混沌性质和分形规律的理想模型之一. 采用逃逸曲线定性比较和分形维数定量计算两种方法, 得到了开口宽度、腔长、拐角位置、圆弧半径等器件参数对逃逸曲线混沌区域分布的影响规律. 结果发现逃逸曲线中存在分形自相似结构, 揭示了粒子在RIKEN介观器件腔中输运过程存在的混沌性质, 并首次运用"眼式结构"分析和相似比比较等方法对分形自相似结构进行了验证. 关键词： 介观器件 混沌性质 分形自相似 分形维数     

瞬态光电流对有机薄膜光伏器件中肖特基接触的研究

制备了结构为氧化铟锡(ITO)/有机半导体/金属的有机薄膜光伏器件,电流--电压曲线显示其具有整流特性但有机半导体和电极间肖特基接触的内建电场方向很难判定.为了研究有机半导体和电极的肖特基接触特性,分别制备了结构为ITO/有机绝缘层/有机半导体/金属和ITO/有机半导体/有机绝缘层/金属的器件,通过调制激光照射下器件的瞬态光电流方向可容易判断有机半导体和电极间肖特基接触的内建电场方向,外加偏压下瞬态光电流的强度变化进一步证实了判断的正确性.     

An analytical approach for studying the resonant states in mesoscopic devices using the phase coherence of electron waves

Based on the phase coherence of electron waves, an analytical method has been proposed to approach the resonant states in mesoscopic devices. The proposed method has been demonstrated that it is valid in the studies of the resonant states in quantum well structures and the ballistic transport in ultrathin MOS devices. The resonant states in mesoscopic devices calculated from the proposed method agree well with those from the quantum mechanical method. The results show that the proposed method is valid in simplifying some quantum issues in mesoscopic devices.