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介观体系输运过程中载流子的离散性导致了散粒噪声.通过测量散粒噪声可以得到传统的基于时间平均值的电导测量无法得到的随时间涨落信息,因而作为一种重要手段在极低温量子输运研究中得到了一定的应用.极低温环境下的噪声测量是一种难度很大的极端条件下的微弱信号测量,通常需要在低温端安装前置放大器并且尽量靠近待测器件以提高测量信噪比和带宽,因此对放大器的噪声水平和功耗都有严格的要求.提出了在稀释制冷机内搭建的散粒噪声测量系统,以及利用此套系统得到了在mK温区超导隧道结散粒噪声的测量结果.自行研制的高电子迁移率晶体管低温前置放大器采用整体封装,便于安装在商用干式稀释制冷机的4 K温区,本底电压噪声为0.25 nV/√Hz,功耗仅为0.754 mW.通过对隧道结进行散粒噪声测量,得到的Fano因子和理论计算吻合. 相似文献
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Majorana零能量模式是自身的反粒子,在拓扑量子计算中有重要应用.本文研究量子点与拓扑超导纳米线混合结构,通过量子点的输运电荷检测Majorana零模式.利用量子主方程方法,发现有无Majorana零模式的电流与散粒噪声存在明显差别.零模式导致稳态电流差呈反对称,在零偏压处显示反常电导峰.电流差随零模式分裂能的增大而减小,随量子点与零模式耦合的增强而增大.另一方面,零模式导致低压散粒噪声相干振荡,零频噪声显著增强.分裂能导致相干振荡愈加明显且零频噪声减小,而量子点与零模式的耦合使零频噪声增强.当量子点与电极非对称耦合时,零模式使电子由反聚束到聚束输运,亚泊松噪声增强为超泊松噪声.稳态电流差结合低压振荡的散粒噪声能够揭示Majorana零模式是否存在. 相似文献
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输运测量是了解物质性质的一个重要手段.本文简单介绍最近在量子气体中实现的输运实验及其主要结论,包括在类似于介观物理器件中的Landauer输运和强相互作用费米气体中的自旋输运行为.我们着重讨论自旋动力学的特殊性以及其由于全同粒子相互作用所导致的特殊自旋扩散流的形式. 相似文献
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应用全带多粒子Monte Carlo模拟方法,研究了钎锌矿相GaN 材料电子的高场输运特性. 模拟中利用了基于第一性原理总能量赝势方法计算得到的纤锌矿GaN的能带结构数据. 用Cartier的方法,计算碰撞电离散射率. 计算得到了电子平均漂移速度和电子平均能量与电场的关系曲线. 电离系数的分析表明当电场强度大于1 MV/cm时,才会有明显的碰撞电离发生,量子产额的分析表明当电子的能量大于7 eV时,量子产额随能量增加迅速增大. 研究了在0—4 MV/cm电场强度范围内电子在各导带的分布,低场下电子全部位于
关键词:
碰撞电离
高场输运
能带结构
Monte Carlo模拟 相似文献
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Majorana费米子是其自身的反粒子, 在拓扑量子计算中有着重要的应用. 利用粒子数表象下的量子主方程方法, 研究双量子点与Majorana费米子混合结构的电子输运特性, 特别是散粒噪声. 有无Majorana费米子耦合的电流与散粒噪声存在明显差别: 有Majorana费米子耦合时稳态电流差呈反对称, 噪声谱呈现相干振荡并且低频噪声显著增强. 量子点与Majorana费米子对称弱耦合时, 零频噪声由"峰"变为"谷", 并且"边谷"展宽逐渐减小; 当对称强耦合时, 零频噪声的谷深增加, "边谷"向高频端移动. 改变系统与电极的耦合强度时, 零频噪声由谷变成峰. 因此, 稳态电流结合散粒噪声可以探测双量子点结构中Majorana费米子是否存在. 相似文献
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针对介观电子谐振腔模型,在由电荷算符本征态构成的新Fock空间中,假设系统具有变换的对称性,通过求解Hamilton算符的本征值方程,给出系统的量子能谱关系.在电荷算符的Fock态下计算能量的量子涨落,分析和研究电子谐振腔的量子能谱性质.结果表明:类似于电荷的量子性,能谱明显地呈现出离散性,其大小决定于谐振腔的电参量、形状因子及栅极所加偏压等因素;而能量的量子涨落却仅与电荷量子、Planck常数以及系统自感有关. 相似文献
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We investigate the shot noise for phase-coherent quantum transport in the chaotic-to-regular crossover regime. Employing the modular recursive Green's function method for both ballistic and disordered two-dimensional cavities, we find the Fano factor and the transmission eigenvalue distribution for regular systems to be surprisingly similar to those for chaotic systems. We argue that, in the case of regular dynamics in the cavity, diffraction at the lead openings is the dominant source of shot noise. We also explore the onset of the crossover from quantum-to-classical transport and develop a quasiclassical transport model for shot noise suppression which agrees with the numerical quantum data. 相似文献
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Q. Chen H. -K. Zhao 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):237-248
We have investigated the spectral density of shot noise for an ultra-small quantum dot(QD) system in the Coulomb blockade
regime when irradiated with microwave fields (MWFs) by employing a nonequilibrium Green’s function technique. The shot noise
is sensitive to Coulomb interaction, and the photon-assisted Coulomb blockade behaviour strongly modifies the mesoscopic transport.
We have calculated the first and second derivatives of shot noise in the strong and weak coupling regimes to compare the theoretical
results with existing experimental results. In the strong coupling regime, the first and second derivatives of shot noise
display Fano type peak-valley structures around the charging channel 2E
c
due to Coulomb interaction. When the magnitudes of the MWFs are sufficiently large, the system displays channel blockade
due to photon irradiation. The photon-assisted and Coulomb blockade steps in the noise — as well as the resonant behaviour
in the differential noise — are smeared by increasing temperature. The Coulomb interaction suppresses the shot noise, but
the ac fields can either suppress the shot noise(balanced case) or enhance the shot noise(unbalanced case). The suppression
of shot noise caused by ac fields in the balanced case is greater than that caused by Coulomb interaction in our system. Super-Poissonian
shot noise may be induced due to the compound effects of strong Coulomb interaction and photon absorption-emission processes. 相似文献
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The reduction of quantum scattering leads to the suppression of shot noise. In this Letter, we analyze the crossover from the quantum transport regime with universal shot noise to the classical regime where noise vanishes. By making use of the stochastic path integral approach, we find the statistics of transport and the transmission properties of a chaotic cavity as a function of a system parameter controlling the crossover. We identify three different scenarios of the crossover. 相似文献
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Shot noise of the spin inelastic tunneling through a quantum dot with single molecule-magnet 下载免费PDF全文
We have studied the quantum fluctuations of inelastic spin-electron scattering in quantum dot with an embedded biaxial single molecule-magnet and particularly investigated the zero-frequency shot noise and Fano factor in different magnetic fields. It is found that the shot noise and Fano factor exhibit a stepwise behaviour as bias increases in the presence of interaction between the electron and molecule-magnet for a weak magnetic field. As magnetic field becomes strong, a dip is displayed in the shot-noise-bias curve due to the suppression of inelastic shot noise caused by the quantum tunneling of magnetisation. Because of the spontaneous inelastic tunneling at zero bias, a small shot noise occurs, which results in the case of Fano factor F >> 1. Moreover, our results show that the sweeping speed can also influence the shot noise and Fano factor obviously. 相似文献
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H.-K. Zhao L.-L. Zhao J. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(3):441-451
We have investigated the shot noise in the mesoscopic system
composed of a quantum dot (QD) coupled to ferromagnetic terminals
under the perturbation of ac fields. The shot noise has been derived
using the nonequilibrium Green's function (NGF) technique to
describe the spin polarization effect along with photon absorption
and emission processes in the Coulomb blockade regime. We have
examined the influence of spin polarization on the shot noise under
the perturbation of ac fields in the nonadiabatic regime.
The Coulomb blockade effect results
in the modification of shot noise compared with the noninteracting
case. The spin orientation contributes a spin valve effect for
controlling electron tunnelling through this QD, and different
resonant forms appear around the Coulomb blockade channel. The
photon-assisted spin-splitting and spin-polarization effect
contributes a photon-assisted spin valve to adjust the electron
tunnelling current and shot noise. The spin-polarization effect
varies the value of the Fano factor. However, it does not change
the noise type from sub-Poissonian to super-Poissonian. 相似文献
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It is shown that the spin-resolved current shot noise can probe attractive or repulsive interactions in mesoscopic systems. This is illustrated in two physical situations: (i) a normal-superconducting junction where the spin-current noise is found to be zero, and (ii) a single-electron transistor where the spin-current noise is found to be Poissonian. Repulsive interactions may also lead to weak attractive correlations (bunching of opposite spins) in conditions far from equilibrium. Spin-current shot noise can also be used to measure the spin relaxation time T1, and a setup is proposed in a quantum dot geometry. 相似文献
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We investigate shot noise for quantum dots whose classical phase space consists of both regular and chaotic regions. The noise is systematically suppressed below the universal value of fully chaotic systems, by an amount which varies with the positions of the leads. We analyze the dynamical origin of this effect by a novel way to incorporate diffractive impurity scattering. The dependence of the shot noise on the scattering rate shows that the suppression arises due to the deterministic nature of transport through regular regions and along short chaotic trajectories. Shot noise can be used to probe phase-space structures of quantum dots with generic classical dynamics. 相似文献
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Photon-assisted shot noise through a quantum dot coupled to Luttinger liquid leads is considered using nonequilibrium-Green-function-method. We find that the effect of ac field on the differential shot noise is different for different intralead electron interaction. The inelastic channels associated with photon-assisted-tunneling can dominate electron transport for some ac parameters. 相似文献
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Electron transport in mesoscopic conductors has traditionally involved investigations of the mean current and the fluctuations of the current. A complementary view on charge transport is provided by the distribution of waiting times between charge carriers, but a proper theoretical framework for coherent electronic systems has so far been lacking. Here we develop a quantum theory of electron waiting times in mesoscopic conductors expressed by a compact determinant formula. We illustrate our methodology by calculating the waiting time distribution for a quantum point contact and find a crossover from Wigner-Dyson statistics at full transmission to Poisson statistics close to pinch-off. Even when the low-frequency transport is noiseless, the electrons are not equally spaced in time due to their inherent wave nature. We discuss the implications for renewal theory in mesoscopic systems and point out several analogies with level spacing statistics and random matrix theory. 相似文献
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S. -H. Ouyang C. -H. Lam J. Q. You 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):67-72
We study electron transport through a quantum dot, connected to non-magnetic leads, in a magnetic field. A super-Poissonian
electron noise due to the effects of both interacting localized states and dynamic channel blockade is found when the Coulomb
blockade is partially lifted. This is sharp contrast to the sub-Poissonian shot noise found in the previous studies for a
large bias voltage, where the Coulomb blockade is completely lifted. Moreover, we show that the super-Poissonian shot noise
can be suppressed by applying an electron spin resonance (ESR) driving field. For a sufficiently strong ESR driving field
strength, the super-Poissonian shot noise will change to be sub-Poissonian. 相似文献