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1.
Using the bosonic numerical renormalization group method, we studied the equilibrium dynamical correlation function C(ω) of the spin operator σ_z for the biased sub-Ohmic spin-boson model. The small-ω behavior C(ω) ∝ω~s is found to be universal and independent of the bias ε and the coupling strength α(except at the quantum critical point α = αc and ε = 0). Our NRG data also show C(ω) ∝χ~2ω~s for a wide range of parameters, including the biased strong coupling regime(ε = 0 and α α_c), supporting the general validity of the Shiba relation. Close to the quantum critical point αc,the dependence of C(ω) on α and ε is understood in terms of the competition between ε and the crossover energy scale ω_0~*of the unbiased case. C(ω) is stable with respect to ε for ε《ε~*. For ε》ε~*, it is suppressed by ε in the low frequency regime. We establish that ε~*∝(ω_0~*)~(1/θ)holds for all sub-Ohmic regime 0≤s 1, with θ = 2/(3s) for 0 s≤1/2 and θ = 2/(1 + s) for 1/2 s 1. The variation of C(ω) with α and ε is summarized into a crossover phase diagram on the α–ε plane. 相似文献
2.
3.
本文基于Lee-Low-Pines幺正变换法,采用Tokuda改进的线性组合算符法研究了Rashba自旋-轨道相互作用效应下量子盘中强耦合磁极化子的性质.结果表明,磁极化子的相互作用能Eint的取值随量子盘横向受限强度ω0、外磁场的回旋频率ωc、电子-LO声子耦合强度α和量子盘厚度L的变化均与磁极化子的状态性质密切相关;磁极化子的平均声子数N随ωc,ω0和α的增加而增大,随L的增加而振荡减小;在Rashba自旋-轨道相互作用效应影响下磁极化子的有效质量将劈裂为m*+,m*-两种,它们随ωc,ω0和α的增加而增大,随L的增加而振荡减小;在研究量子盘中磁极化子问题时,电子-LO声子耦合和Rashba自旋-轨道相互作用效应的影响不可忽略,但Rashba自旋-轨道相互作用和极化子效应对磁极化子的影响只有在电子运动的速率较慢时显著. 相似文献
4.
Sina Khorasani 《理论物理通讯》2018,70(3):344-360
We present a detailed calculation of the linear and nonlinear optical response of four types of monolayer twodimensional (2D) transition-metal dichalcogenides (TMDCs), having the formula MX2 with M=Mo, W and X=S, Se. The calculations are based on 6-band tight-binding model of TMDCs, and then performing a semi-classical perturbation analysis of response functions. We numerically calculate the linear χμν(1) (-ω;ω) and nonlinear surface susceptibility tensors χμνζη(3)(-ωΣ; ωr; ωs; ωt) with ωΣ=ωr+ωs+ωt. Both non-degenerate and degenerate cases are studied for thirdharmonic generation and nonlinear refractive index, respectively. Computational results obtained with no external fitting parameters are discussed regarding two recent reported experiments on MoS2, and thus we can confirm the extraordinarily strong optical nonlinearity of TMDCs. As a possible application, we demonstrate generation of a π/4-rotated squeezed state by means of nonlinear response of TMDCs, in a silica micro-disk resonator covered with the 2D material. Our proposed method will enable accurate calculations of nonlinear optical response, such as four-wave mixing and highharmonic generation in 2D materials and their heterostructures, thus enabling study of novel functionalities of 2D photonic integrated circuits. 相似文献
5.
FAN Hong-Yi YAN Peng 《理论物理通讯》2007,48(3):428-430
By virtue of the technique of integration within an ordered product of operators, we derive the normal ordering expansion of a one- and two-mode combination squeezing operator for two harmonic oscillators with coordinate- momentum coupling. It turns out that this squeezing operator just diagonalizes the Hamiltonian H=p^21/2m1+m1ω^21x^21/2+p^222m2+m2ω^22x^22/2-λx2p1 so its ground state is a one- and two-mode combination squeezed state. Quantum fluctuation in the ground state is calculated. 相似文献
6.
The equilibrium geometries, potential energy curves, spectroscopic dissociation energies of the ground and low-lying electronic states of He2, He2+ and He2++ are calculated using symmetry adapted cluster/symmetry adapted cluster-configuration interaction (SAC/SAC-CI) method with the basis sets CC-PV5Z. The corresponding dissociation limits for all states are derived based on atomic and molecular reaction statics. The analytical potential energy functions of these states are fitted with Murrell--Sorbie potential energy function from our calculation results. The spectroscopic constants Be, α e, ω e, and ω e χ e of these states are calculated through the relationship between spectroscopic data and analytical energy function, which are in well agreement with the experimental data. In addition, the origin of the energy barrier in the ground state X1Σg+ of He2++ energy curve are explained using the avoided crossing rules of valence bond model. 相似文献
7.
It is shown that the resonant frequency ωc* of a magnetopolaron bound to a Coulomb impurity in a GaAs/Ga1-xAlx AS quantum well is lower than that oflongitudinal optical (LO) phonons owing to the effect of the Coulomb potential. Using MacDonald method to treat the Coulomb potential we come to the conclusion that ωc* is really below the frequency of LO phonons but not "pinning" at a frequency near that of TO phonons. 相似文献
8.
We investigate spin squeezing of a collective spin system governed by mixed Hamiltonian of the one-axis twisting and two-axis counter-twisting with decay. The analytic solutions of the optimally squeezed angle and the spin squeezing parameter are derived. It is shown that the two-axis counter-twisting Hamiltonian induces stronger spin squeezing than the one-axis twisting one. It is also shown that the decay rate has no effect on the size of the squeezing parameter, it only affects the period of squeezing parameter. 相似文献
9.
对于玻璃珠组成的颗粒介质样品,本文测量了横波和纵波声速,同时分析了剪切模量(G)与体积模量(B)的比值(G/B)随压强的变化规律.结果表明,在低压强下,颗粒体系的纵波声速(C_L)明显大于横波声速(c_T),且体系的CL,CT及G/B均随压强p变化呈幂律标度,即CL∝p~(0.3817),CT∝p~(0.2809)G/B∝p~(-0.4539),幂指数与文献[1]中预言的-1/2非常接近,暗示在我们实验压强范围内的颗粒样品处于L玻璃状态.此外,本文还利用快速傅里叶变换法测量了玻璃珠样品中的声学衰减特性及二阶谐波随压强的变化,发现:纵波声衰减系数(α)、接收端二倍频振幅(μ_(2ω))与基频振幅(μ_(1ω))平方的比值(μ_(2ω)/μ_(1ω)~2)均随压强的增大而幂率减小,分别为α∝p~-(-0.1879),和μ_(2ω)/μ_(1ω)~2∝p~(-0.866). 相似文献
10.
Zong-Fu JIANG 《理论物理通讯》1993,19(3):289-294
We explore the properties of the quantum kicked harmonic osciUation governed by the Hamiltonian H=1/2p2+1/2ω02x2-K cos x∑n=-∞∞δ(t/T - n): The classical version of this model is known to exhibit certain type of stochastic behavior. We reduce the quantum equation of the model td quantum mapping equations. Numerical results of the mappings show that the behavior of the average energy as a function of time depends on the ration of the frequency of the external (2π/T) and that of the unperturbed system wo. The energy increases first very rapidly and then the energy growth saturates for irrational ω0T/2π. The break time is independent of the strength of the external force, but is roughly proportional to 1/ω0T.For a fixed rational ω0T/2πt,h e energy is damped oscillation for smaller T , a nd it is seemingly recurrent with time in the sense of Hogg and Huberman. In both cases, these behaviors of energy are independent of the strength of the external force and differ from the behavior of the quantum kicked rotator. 相似文献
11.
It is shown that the slowly varying amplitudes of both high and low frequency extraordinary waves propagating perpendicular to the dc magnetic field in ferromagnetic systems are described by the nonlinear SchrEdinger equation. The extraordinary waves are modulationally stable (unstable) and may evolve as dark (bright) solitons as the frequency ω satisfies ω0 < ω < ωb or ω > ω1(0 < ω < ω0 or ωa ≤ ω < ω1), where ωa, ωb, ω0 and w1 are given in the text. 相似文献
12.
通过电子注入的方法制备了含氮空位色心单光子源的金刚石荧光纳米颗粒. 自旋回声测试结果表明, 纳米颗粒中氮空位色心的相干时间T2很短, 介于0.86 μs至5.6 μs之间. Ramsey干涉条纹测试结果表明, 氮空位色心NV1点的退相干时间T2* 最大, 为0.7 μs, 其电子自旋共振谱可分辨的最小线宽为1.05 MHz. 并且NV1点的电子自旋共振谱可分辨氮空位色心本身的14N核自旋与 氮空位色心电子自旋之间的2.2 MHz超精细相互作用, 这对于在金刚石纳米颗粒中实现核自旋的操控和多个量子比特的门操作具有重要意义.
关键词:
纳米颗粒
氮空位色心
电子自旋 相似文献
13.
Ramachandran K. Tripathi V.K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1997,25(3):423-426
A long wavelength Langmuir wave (ω0, k0), propagating through a parabolic plasma density channel, can decay into a low-frequency mode (ω,k&oarr;) and two short wavelength Langmuir wave sidebands (ν1,2,k&oarr;1,2 ), via two-stream instability where ω1,2=ω∓ω0 and k&oarr;1,2=k&oarr;∓k&oarr;0. Depending on the mode number n, the growth rate maximizes in the range γmax≃0.1ωpi-0.4ωpi for the range of k from 0.1(ωpi/cs) to 0.2(ωpi/cx) for ν0~νth where ν0 and νth are the oscillatory and thermal velocities of electrons, ωpi is the ion plasma frequency on the axis, and cs is the sound speed. The growth rate increases with the width a of the plasma density channel. It decreases with the mode number. The instability may be relevant to laser based charged particle accelerators 相似文献
14.
Ramachandran K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1996,24(2):487-489
A high-power linearly polarized laser propagating through a plasma produces oscillatory electron velocity at the second harmonic due to-the ν&oarr;×B&oarr; force, This velocity couples a Langmuir wave (ω, k&oarr;) and an electromagnetic wave (ω1, k&oarr;1), where ω1=ω-2ω0 , k-2k&oarr;0 and ω0, k&oarr;0 are frequency and wavenumber of the laser pump, causing second harmonic Raman scattering. The growth rate is maximum for side scattering. This process can occur above the quarter critical density, unlike the first harmonic stimulated Raman scattering which occurs below the quarter critical density 相似文献
15.
Theoretical study of spin-forbidden cooling transitions of indium hydride using ab initio methods
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The feasibility of spin-forbidden cooling of the In H molecule is investigated based on ab initio quantum chemistry calculations. The potential energy curves for the X~1Σ_(0~+)~+, a~3Π_~(0~-), a~3Π_(0~+), a~3Π_1, a~3Π_2, A~1Π_1, 1~3Σ_(0~-)~+, and 1~3Σ_1~+states of In H are obtained based on multi-reference configuration interaction plus the Davidson corrections method. The calculated spectroscopic constants are in good agreement with the available experimental data. In addition, the influences of the active space and spin–orbit coupling effects on the potential energy curves and spectroscopic constants are also studied. For Re of a~3Π_(0~-), a~3Π_(0~+), a~3Π_1, and a~3Π_2 states, the error from large active space is small. The potential energy curve of the A~1Π_1state is not smooth for small active space. The spin–orbit coupling effects have great influences on the potential well depth and equilibrium internuclear distance of the A~1Π state. The Franck–Condon factors and radiative lifetimes are obtained on the basis of the transition dipole moments of the a~3Π_(0~+) → X~1Σ_(0~+)~+, a~3Π_1 → X~1Σ_(0~+)~+, and A~1Π_1 → X~1Σ_(0~+)~+ transitions. Our calculation indicates that the a~3Π_1( ν'= 0) → X~1Σ_(0~+)~+(ν = 0) transition provides a highly diagonally distributed Franck–Condon factor and a short radiative lifetime for the a3Π1 state, which can ensure rapid and efficient laser cooling of In H.The proposed laser drives a~3Π_1 → X~1Σ_(0~+)~+ transitions by using three wavelengths. 相似文献
16.
利用考虑Davidson修正的内收缩多参考组态相互作用(icMRCI+Q)方法结合相关一致基组aug-ccpV6Z计算了AlH~+离子前两个离解极限对应的5个Λ-S态和10个?态的势能曲线.为了提高势能曲线的可靠性和精确性,计算中考虑了自旋轨道耦合效应、芯电子价电子相关和标量相对论修正以及将势能外推至完全基组极限.基于得到的势能曲线,获得了束缚和准束缚的4个Λ-S态和8个?态的光谱常数和振动能级,与已有的实验结果符合.计算了2(1/2)→X~2Σ_(1/2)~+和A~2Π_(3/2)→X~2Σ_(1/2)~+跃迁的跃迁偶极距.利用计算的精确的势能曲线和跃迁偶极矩,获得了2(1/2)~(第一势阱)(υ′=0, 1)→X~2Σ_(1/2)~+(υ′′)和A~2Π_(3/2)(υ′=0, 1)→X~2Σ_(1/2)~+(υ′′)跃迁的高度对角化分布的Franck-Condon因子(f_(00)和f_(11))和大的振动分支比;预测了2(1/2)~(第一势阱)(υ′=0, 1)和A~2Π_(3/2)(υ′=0, 1)态短的自发辐射寿命和窄的辐射宽度,这适合于AlH~+离子的快速激光致冷.所需的3束激光冷却波长都在紫外区域.这些结果表明了激光冷却AlH~+离子的可行性.此外,评估了自旋轨道耦合效应对光谱常数、振动能级和激光冷却AlH~+离子的影响. 相似文献
17.
钙钛矿型锰氧化物(La$lt;sub$gt;0.8$lt;/sub$gt;Eu$lt;sub$gt;0.2$lt;/sub$gt;)$lt;sub$gt;4/3$lt;/sub$gt;Sr$lt;sub$gt;5/3$lt;/sub$gt;Mn$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;7$lt;/sub$gt;的磁性和电性研究
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采用传统固相反应法制备钙钛矿型锰氧化物 (La0.8Eu0.2)4/3Sr5/3Mn2O7多晶样品, X-射线衍射分析表明, 样品(La0.8Eu0.2)4/3Sr5/3Mn2O7结构呈现良好的单相. 通过磁化强度随温度的变化曲线(M-T)、不同温度下磁化强度随磁场的变化曲线(M-H)和电子自旋共振谱发现: 在300 K以下, 随着温度的降低, 样品先后经历了二维短程铁磁有序转变 (TC2D ≈ 282 K)、三维长程铁磁有序转变(TC3D ≈ 259 K)、奈尔转变(TN ≈ 208K)和电荷有序转变(TCO ≈ 35 K); 样品 (La0.8Eu0.2)4/3Sr5/3Mn2O7在TN以下, 主要处于反铁磁态; 在TC3D达到370 K时, 样品处于铁磁-顺磁共存态, 在370 K以上时样品进入顺磁态. 此外, 分析电阻率随温度的变化曲线(ρ-T)得到: 样品在金属-绝缘转变温度(TP ≈ 80 K)附近出现最大磁电阻值, 其位置远离TC3D, 表现出非本征磁电阻现象, 其磁电阻值约为61%. 在TCO以下, 电阻率出现明显增长, 这是由于温度下降使原本在高温部分巡游的eg电子开始自发局域化增强所致. 通过对 (La0.8Eu0.2)4/3Sr5/3Mn2O7的ρ-T 曲线拟合, 发现样品在高温部分的导电方式基本遵循小极化子的导电方式.
关键词:
磁性
电性
金属-绝缘转变温度
电子自旋共振 相似文献
18.
FAN Hong-yi 《理论物理通讯》1990,14(2):181-188
We point out that the compact exponential operator V≡exp[-i(λ1Q2-λ2P2)/2] (where λ1, λ2 are real;P and Q are momentum and coordinate operators, respectively;the units of h=m=ω=l is taken, m and ω are harmonic oscillator's mass and'frequency, respectively) is a generalized single-mode squeeze operator which can generate mixed squeezing and rotating transformations. The decomposition of V as a product of a squeeze operator and a rotating operator is derived through the technique of integration within an ordered product.The fluctuation in quadrature phases for the squeezed vacuum state generated by V is analyzed. 相似文献
19.
We investigate in detail the effects of R-parity lepton number violation on the decay b1→bχ10 in
the R-parity violating minimal supersymmetric standard model
(Rp-MSSM) under the present experimental constraints
on Rp parameters. In our numerical calculations we
consider two cases of input parameters of the squark and slepton sectors,
Msquark<Mslepton and
Msquark>Mslepton, for comparison. The results show that the relative R-parity violating correction is not very sensitive to the mass of the lightest neutralino
χ10 and the degenerate R-parity violating
coupling parameter λ2, but strongly depends on
Msquark,
Mslepton, tan β and the
degenerate R-parity violating coupling parameter λ1. The relative correction is about -4~3% and can exceed -6% in some region of parameter space. Therefore, precise experiment analyses on the decay
b1→bχ10
may provide a probe of the R-parity violation. 相似文献
20.
The surface impedance γ and the penetration depth δ of the electromagnetic field was calculated for a polycrystalline conductor under the conditions of the normal skin effect. The polycrystal is composed from the single-phase slightly anisotropic single-crystalline grains of arbitrary symmetry. Corrections (γ-γ0)/γ0 and (δ-δ0)/δ0 due to the polycrystallinity are functions of the parameter ζ=δ0/a, where γ0 and δ0 are the impedance and the penetration depth of the isotropic conductor with the conductivity σ0=Sp σik/3, σik is the separate grain conductivity tensor, and a is the mean size of a grain.
The effective conductivity of a polycrystal can be obtained either from the impedance γ (σef(γ)) or from the penetration depth δ (σef(δ)) It was found that σef(γ)≠σef(δ) The corrections (σ-σef((γ))/σ0 and (σ0-σef(δ))/σ0 depend on the frequency of the incident wave.
The obtained results are also applicable in the infrared spectrum region. It was shown that, just as for the isotropic conductor, there is the total reflection of the electromagnetic wave from the polycrystal surface.
It was necessary to examine the oblique incidence of an electromagnetic wave onto the surface of an isotropic metal for the substantiation of the set of the boundary conditions used. 相似文献
The effective conductivity of a polycrystal can be obtained either from the impedance γ (σef(γ)) or from the penetration depth δ (σef(δ)) It was found that σef(γ)≠σef(δ) The corrections (σ-σef((γ))/σ0 and (σ0-σef(δ))/σ0 depend on the frequency of the incident wave.
The obtained results are also applicable in the infrared spectrum region. It was shown that, just as for the isotropic conductor, there is the total reflection of the electromagnetic wave from the polycrystal surface.
It was necessary to examine the oblique incidence of an electromagnetic wave onto the surface of an isotropic metal for the substantiation of the set of the boundary conditions used. 相似文献