共查询到20条相似文献,搜索用时 156 毫秒
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振动弛豫时间是可激发气体分子内外自由度能量转移速率的宏观体现,它决定了声吸收谱峰值点对应的弛豫频率.本文给出了等温、绝热定压和绝热定容三种不同热力学过程下振动弛豫时间的相互关系;基于Petculescu和Lueptow[2005 Phys.Rev.Lett.94 238301]的弛豫过程合成算法,推导了单一压强下两频点声测量值的弛豫时间重建算法.该算法可应用于等温、绝热定压、绝热定容弛豫时间和弛豫频率的重建测量,并避免了弛豫时间传统声测量方法需要不断改变气体腔体压强的问题.仿真结果表明,对于室温下CO_2,CH_4,Cl_2,N_2和O_2组成的多种气体,重建的弛豫时间和弛豫频率与实验数据相符. 相似文献
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根据电子自旋轨道耦合对自旋极化弛豫影响的DP机理进一步导出了半导体中电子自旋弛豫与动量弛豫及载流子浓度的关系,并采用飞秒抽运探测技术在室温下测量AlGaAs/GaAs 多量子阱中载流子浓度在 1×1017—1×1018cm-3范围内,电子自旋弛豫时间由58ps增加至82 ps的变化情况,与理论计算值符合,说明了随着载流子浓度的增加,载流子间的频繁散射加速了电子动量驰豫,减弱了电子自旋轨道耦合作用,从而延长了电子自旋寿命.
关键词:
电子自旋轨道耦合
电子自旋弛豫和动量弛豫
飞秒光谱技术 相似文献
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在水相合成CdTe以及CdTe/CdS核壳结构量子点基础上, 利用基于抽运-探测技术的瞬态差分透射技术研究了CdTe量子点以及不同CdS壳层厚度的CdTe/CdS量子点的最低激子能态的超快激发与弛豫动力学. 研究表明:相比于CdTe,CdTe/CdS量子点的电子空穴由于空间分离,其所需的激发时间要长于电子空穴空间重叠态所需要的激发时间.随着壳层厚度的增加, 量子点表面的钝化有效地减少了表面态相关弛豫机理,并延长相对应的弛豫时间. 相似文献
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《物理学报》2017,(4)
采用时间分辨圆偏振光抽运-探测光谱,测量了(110)晶向生长的近似对称和完全非对称掺杂GaAs/AlGaAs量子阱中的电子自旋弛豫,发现两种量子阱材料中的电子自旋弛豫时间随载流子浓度的增大均呈现出先增大后减小的趋势,且近似对称掺杂GaAs量子阱中的电子自旋弛豫时间明显大于完全非对称掺杂量子阱.分析表明,在(110)晶向生长的GaAs量子阱中并非只有通常认为的Bir-Aronov-Pikus(BAP)机理起作用,在低载流子浓度区域,两种量子阱中D′yakonov-Perel′(DP)机理起主导作用,高载流子浓度区域BAP机理和DP机理都起作用,完全非对称掺杂的量子阱中DP机理强于近似对称掺杂量子阱. 相似文献
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 ̄14N核四极共振自旋系统的自旋-晶格弛豫是一种双指数弛豫。本文介绍了 ̄14N核四极共振自旋系统的自旋-晶格弛豫时间的3种测量方法,利用可变多面体方法对实验数据进行拟合,获得了 ̄14N核四极共振自旋系统的自旋-晶格弛豫时间T_1s和T_11,对有关文献中关于核四极共振弛豫时间的测量的3个观点提出了质疑。 相似文献
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14N核四极共振自旋系统的自旋-晶格弛豫是一种双指数弛豫。本文介绍了14N核四极共振自旋系统的自旋-晶格弛豫时间的3种测量方法,利用可变多面体方法对实验数据进行拟合,获得了14N核四极共振自旋系统的自旋-晶格弛豫时间T1s和T11,对有关文献中关于核四极共振弛豫时间的测量的3个观点提出了质疑。 相似文献
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We use an ensemble Monte Carlo simulation of coupled electrons, holes and nonequilibrium polar optical phonons in multiple quantum well systems to model the intersubband relaxation of hot carriers measured in ultra-fast optical experiments. We have investigated the effect of various models of confined photon modes on the energy relaxation and intersubband transition rate in single quantum well and coupled well systems. In particular, the symmetry of the atomic displacement with respect to the quantum well has a marked effect on the relative intersubband versus intrasubband scattering rates, depending on whether one considers electrostatic boundary conditions(slab modes) or mechanical boundary conditions(guided modes). In single quantum wells systems, the overall intersubband relaxation time is not found to be strongly dependent on the confined mode model used due to competing effects of hot phonons and the relative intrasubband scattering rates. For coupled well systems, the relaxation rate is much more dependent on the exact nature of the phonon amplitude. Large effects are found associated with localized AlAs interface modes which dominate the intersubband relaxation time. 相似文献
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通常单量子信号的强度在Raman磁共振谱中要比其它多量子信号的强度大得多,因而易引起接收机饱和,使信号发生变形,不利于多量子信号的检测,因此压抑强的单量子峰是必要的.积算符理论分析表明,异核体系Raman磁共振谱的单,多量子峰的共振频率及其信号强度关于频偏满足对称关系:当频偏由正变为负时,单量子信号的强度亦随之改变了符号.因此,对正负频偏(数值相等)的两次Raman磁共振实验的FID信号进行累加,就可压抑强的单量子峰,而对于多量子峰则在大的频偏条件下不会相互抵消.因此,这样的实验累加可以保持多量子信号的强度而压抑掉强的单量子峰.作为实验验证,我们给出了异核AXn体系(CHCl3,CH2Cl2,CH3OH)的按上述正负频偏循环累加采样方法得到Raman磁共振13C实验谱.实验结果同理论预言完全一致. 相似文献
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《Comptes Rendus Physique》2008,9(1):119-126
A software package has been designed to simulate nuclear magnetic resonance spectra and images. Combining the product operator matrix with the non-linear Bloch equations, the software can efficiently simulate classical and quantum effects including scalar coupling, dipolar coupling, translational diffusion, chemical shift, radiation damping, transverse relaxation, and longitudinal relaxation. One of the most unique features of the software is its ability to incorporate effects of inter- and intra-molecular multiple quantum coherences in complex multiple-spin coupled systems, which are difficult with other existing software packages. The software, written in Visual C++, has a friendly graphical user interface and is easy to use. To cite this article: C. Cai et al., C. R. Physique 9 (2008). 相似文献
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We present a new readout method for a superconducting flux qubit, based on the measurement of the Josephson inductance of a superconducting quantum interference device that is inductively coupled to the qubit. The intrinsic flux detection efficiency and backaction are suitable for a fast and nondestructive determination of the quantum state of the qubit, as needed for readout of multiple qubits in a quantum computer. We performed spectroscopy of a flux qubit and we measured relaxation times of the order of 80 micros. 相似文献
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We present a variational theory for the optimal control of quantum systems with relaxation over a finite time interval. In our approach, which is a nontrivial generalization of previous formulations and which contains them as limiting cases, the optimal control field fulfills a high-order Euler-Lagrange differential equation, which guarantees the uniqueness of the solution. We solve this equation numerically and also analytically for some limiting cases. The theory is applied to two-level quantum systems with relaxation, for which we determine quantitatively how relaxation effects limit the control of the system. 相似文献
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We investigate heavy-hole spin relaxation and decoherence in quantum dots in perpendicular magnetic fields. We show that at low temperatures the spin decoherence time is 2 times longer than the spin relaxation time. We find that the spin relaxation time for heavy holes can be comparable to or even longer than that for electrons in strongly two-dimensional quantum dots. We discuss the difference in the magnetic-field dependence of the spin relaxation rate due to Rashba or Dresselhaus spin-orbit coupling for systems with positive (i.e., GaAs quantum dots) or negative (i.e., InAs quantum dots) g factor. 相似文献
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DIRECT MEASUREMENT OF TRANSVERSE RELAXATION TIME OF INTERMOLECULAR MULTIPLE QUANTUM COHERENCES IN NMR 总被引:4,自引:0,他引:4
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A one-dimensional NMR method is presented for measuring the transverse relaxation time, T2,n, of intermolecular multiple quantum coherences (IMQCs) of coherence order n in highly polarized spin systems. The pulse sequence proposed in this paper effectively suppresses the effects of radiation damping, molecular diffusion, inhomogeneity of magnetic field, and variations of dipolar correlation distance, all of which may affect quantitation of T2,n. This pulse sequence can be used to measure not only IMQC transverse relaxation time T2,n(n>1) quickly and directly, but also the conventional transverse relaxation time. Experimental results demonstrate that the quantitative relationship between T2,n(n≥1) and T2 is T2,n≈T2/n. These results will be helpful for understanding the fundamental properties and mechanisms of IMQCs. 相似文献
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Quantum chemical methods originally developed for studying atomic and molecular systems can be applied successfully to the study of few-body electron-hole systems in semiconductor nanostructures. A new computational approach is presented for studying the energetics and dynamics of interacting electrons and holes in a semiconductor quantum dot. The electron-hole system is described by a two-band effective mass Hamiltonian. The Hamiltonian is diagonalized in a configuration state function basis constructed as antisymmetric products of the electron one-particle functions and antisymmetric products of the hole one-particle functions. The symmetry adapted basis set used for the expansion of the one-particle functions consists of anisotropic Gaussian basis functions. The transition probability between electron-hole states consisting of different numbers of carrier pairs is calculated at the full configuration interaction level. The results show that the electron-hole correlation affects the radiative recombination rates significantly. A method for calculating the phonon relaxation rates between excited states and the ground state of quantum dots is described. The phonon relaxation calculations show that the relaxation rate is strongly dependent on the energy level spacings between the states. 相似文献