CaBa-铝酸盐玻璃中Cr4+谱线宽度随温度的变化

测量了15~300K温度范围内57.5%Al_1.5O-35%CaO-7.5%BaO玻璃中四价铬的发射光谱.这种材料中铬离子的能级处于Tanabe-Sugano图上弱场范围中,最低的激发态是³T₂,发射谱是一个宽带.按照单频近似理论拟合低温下的光谱,得到³T₂能级的零声子线位置E_zp=8400cm^-1,声子能量tω=320cm^-1,黄昆因子S=358.尽管单频近似能够较好地描述低温下的线形,发射光谱宽度随温度的变化却与单频近似理论的结果不符.讨论了这种差别的原因,认为可能的解释是与激发态耦合的声子能量大于与基态耦合的声子能量.     

Vibronic sidebands in ruby

An experimental and group-theoretical study of single phonon vibronic sidebands of theR-lines in ruby has been performed. Restrictions in the electron-phonon-spectra due to crystal symmetry occur only inEC-polarization and for phonons withk-vectors zero or parallel to theC-axis. An analysis of the fluorescence and excitation spectra led to an identification of part of the lines in the vibronic sidebands with normal modes of the lattice. In the regime of acoustical phonons the intensity of the sideband increases with frequency following a potential law with an exponent of slightly less than 5. A strong enhancement of the vibronic transition probability was found on the high frequency side of theR-lines due to a resonance with the electronic transitions⁴ A ₂-² T ₁. Crosssections of the vibronic transitions in the spectral range of Stokes- and anti-Stokessidebands are given in a diagram. For acoustical phonons with energies up to 6 THz they are also expressed in a formula.     

Motional averaging in an excited state of ZnS: Cu2+

The single isotropic g factor found in the ²E excited state of ZnS:Cu²⁺ is hard to reconcile with the properties of this state, in particular with the moderate strength of the E ? ? vibronic coupling. A vibronic coupling between this state and the vibronic levels of the ground ²T₂ state due to τ₂ modes can bring about motional averaging between strain split states of ²E through a two phonon non-resonant process. In general, excited state mechanisms will be effective between states of the same spin multiplicity and which have large Stoke shifts.     

Vibronic problem in the higher excited states of F-center in alkali halides

Vibronic problem in the higher excited states of F-center in alkali halidesA new approach to the vibronic problems of bound polaron is proposed, taking advantage of the spherical symmetry of the system. By applying the obtained formula to the analysis of the transient absorption spectra due to the transition from the relaxed excited state to higher excited states of F-center in alkali halides, a good fit between the theory and the experiments is obtained and the final states of the transition are assigned to be 3p state and its phonon side bands perturbed through vibronic coupling.     

The influence of surfaces and interfaces on coherent phonons in semiconductors

Experiments have shown that ultrafast optical excitation of semiconductors can produce oscillating changes in the optical properties of the material. The frequency of the oscillations in transmission or reflection usually matches one of the phonon modes, typically theq = 0 optical mode. These oscillations are known as coherent phonons. We discuss the role of surfaces and interfaces on the coherent phonon signal. We show that: (1) the coherent phonon signal can be used as a probe of the surface depletion field and (2) multiple interfaces as in a superlattice, can drastically alter the coherent phonon spectrum: screening of the modes in the superlattices is reduced and acoustic modes can now be excited.     

Fröhlich 极化子的非经典基态

本文计及波矢 q,q' 声子间动力学关联效应,采用双模-压缩(声子)相干态作为再一次正则变换方案,基于Huybrechts变分近似,求解 Fröhlich 大极化子的非经典基态.由于双模-压缩(声子)相干态导致声子相干态-压缩声子态关联效应,相干参量 f_q 与双模压缩角 φqq' 关键词： 双模-压缩(声子)相干态 位移-声子压缩态 Frö hlich 极化子 非经典基态     

On the theory of lasing at vibronic transitions in impurity crystals

Some aspects of lasing at vibronic transitions in impurity crystals are theoretically studied. The threshold conditions for a vibronic laser are shown to be dependent on the strength of the interaction of optical centers with a local vibration, which forms the vibronic spectrum, and the crystal lattice temperature. The theory can easily be generalized to the spectrum containing a structureless phonon sideband and well agrees with the experimental temperature dependence of the output power of a Mg₂SiO₄:Cr⁴⁺ forsterite laser.     

Vibronic coupling and implications in the copper related 1.014 eV photoluminescence spectrum in silicon

The 1.014 eV photoluminescence spectrum observed in Cu diffused, quenched silicon crystals exhibits a characteristic strong phonon sideband structure. It is shown that the intensity decrease of the no-phonon transition from 4.2 to 40 K is not due to vibronic coupling but originates in the population of excited electronic states of the defect. The thermal luminescence data and published lifetime measurements can consistently be explained by the electronic level scheme which was recently proposed.     

Properties of ground state and anomalous quantum fluctuations in one-dimensional polaron-soliton systems—the effects of electron-two-phonon interaction and non-adiabatic quantum correlations

Based on the Holstein model Hamiltonian of one-dimensional molecular crystals, by making use of the expansion approach of the correlated squeezed-coherent states of phonon instead of the two-phonon coherent state expansion scheme, the properties of the ground state and the anomalous quantum fluctuations are investigated in a strongly coupled electron-phonon system with special consideration of the electron-two-phonon interaction. The effective renormalization (αi) of the displacement of the squeezed phonons with the effect of the squeezed-coherent states of phonon and both the electron-displaced phonon and the polaron-squeezed phonon correlations have been combined to obtain the anomalous quantum fluctuations for the corrections of the coherent state. Due to these non-adiabatic correlations, the effective displacement parameter αi is larger than the ordinary parameter α (0) i . In comparison with the electron-one-phonon interaction (g) corrected as αig, we have found the electron-two-phonon interaction (g1) corrected as αi2 g1 is enhanced significantly. For this reason, the ground state energy (E(2) 0 ) contributed by the electron-two-phonon interaction is more negative than the single-phonon case (E(1) 0 ) and the soliton solution is more stable. At the same time, the effects of the electron-two-phonon interaction greatly increase the polaron energy and the quantum fluctuations. Furthermore, in a deeper level, we have considered the effect of the polaron-squeezed phonon correlation (f-correlation). Since this correlation parameter f > 1, this effect will strengthen the electron-one and two-phonon interactions by fαig and f2αi2 g1, respectively. The final results show that the ground state energy and the polaron energy will appear more negative further and the quantum fluctuations will gain further improvement.     

带有电子-双声子相互作用的一维铁磁性介观环的非经典本征态和非经典本征持续电流

在一维铁磁性织构介观环的基础上, 计及电子-双声子相互作用, 介入了三项非经典效应抑制电子-单声子相互作用引起的量子涨落效应: 1) 跳步电子-单声子相干态关联效应;2) 由压缩相干态引起的声子压缩态-单声子相干态间过程关联效应;3) 声子位移-声子压缩态的表象关联效应．从结果来看, 电子-双声子相互作用明显加强了压缩效应(增大压缩参量), 而跳步电子-单声子相干态关联效应引起本征能量大幅度下降, 持续电流大幅度增加．特别是介入了声子压缩态-单声子相干态间过程关联效应后, 声子压缩参量远大于理想压缩态相应的压缩参量, 有效地抑制了Debye-Waller(D-W)效应．当声子压缩态-单声子相干态间过程关联与声子位移重整化效应结合在一起时, 声子场的压缩将更大幅度地增加, D-W效应(参量w_ph)将更大幅度地减小, w_ph << w_ph⁽⁰⁾, 从而极大幅度地抑制了电子-单声子相互作用导致的量子涨落效应. 这样一来, 非经典态本征能量E_n极大幅度地下降, E_n << E_n⁽⁰⁾, 与此同时, 本征持续电流振幅I_n 则极大幅度地增大, I_n >> I_n⁽⁰⁾.     

On the power from phonon fluorescence in superconductors

A vibronic sideband spectrometer is used to detect phonons generated from phonon fluorescence in superconductors. Although previously projected phonon powers are just within the minimum detectivity, no sideband signals were observed. An interpretation of this result is given.     

Theoretical investigation of superconductivity in ternary silicide NaAlSi with layered diamond-like structure

We have investigated the electronic structure, phonon modes and electron–phonon coupling to understand superconductivity in the ternary silicide NaAlSi with a layered diamond-like structure. Our electronic results, using the density functional theory within a generalized gradient approximation, indicate that the density of states at the Fermi level is mainly governed by Si p states. The largest contributions to the electron–phonon coupling parameter involve Si-related vibrations both in the x–y plane as well as along the z-axis in the x–z plane. Our results indicate that this material is an s-p electron superconductor with a medium level electron–phonon coupling parameter of 0.68. Using the Allen–Dynes modification of the McMillan formula we obtain the superconducting critical temperature of 6.98 K, in excellent agreement with experimentally determined value of 7 K.     

Dynamical behavior of a mesoscopic circuit in phonons bath derived by virtue of the IWOP technique

Taking into account the interactions between electrons and phonons, we study the dynamic behavior of a dissipative mesoscopic circuit for pure initial coherent state of phonon bath modes by virtue of the IWOP technique. It shows that if the bath modes are initially in coherent states, some phenomena like Brownian behavior will appear in mean charge and current of the mesoscopic circuit. The quantum fluctuations of charge and current are constant and irrelevant to the coupled coefficients between electrons and phonons.     

Theory of non-Markovian dynamics in resonance fluorescence spectrum

We present a detailed theoretical study of non-Markovian dynamics in the fluorescence spectrum of a driven semiconductor quantum dot (QD), embedded in a cavity and coupled to a three-dimensional (3D) acoustic phonon reservoir. In particular, we investigate the effect of pure dephasing on one of the side-peaks of the Mollow-triplet spectrum, expressed in terms of the off-diagonal element of the reduced system operator. The QD is modeled as a two-level system with an excited state representing a single exciton, and ground state represents the absence of an exciton. Coupling to the radiative modes of the cavity is treated within usual Born–Markov approximation, whereas dot-phonon coupling is discussed within non-Markovian regime beyond Born approximation. Using an equation-of-motion technique, the dot-phonon coupling is solved exactly and found that the exact result coincides with that of obtained within Born approximation. Furthermore, a Markov approximation is carried out with respect to the phonon interaction and compared with the non-Markovian lineshape for different values of the phonon bath temperature. We have found that coupling to the phonons vanishes for a resonant pump laser. For a non-resonant pump, we have characterized the effect of dot-laser detuning and temperature of the phonon bath on the lineshape. The sideband undergoes a distinct narrowing and acquires an asymmetric shape with increasing phonon bath temperature. We have explained this behavior using a dressed-state picture of the QD levels.     

Kerr效应对非线性J-C模型辐射谱的影响

研究了Kerr介质腔中非线性J-C模型的辐射谱.导出了双模初始光场处于任意量子态时辐射谱的计算公式,给出了光场处于数态、相干态和压缩真空态时的数值结果,讨论了Kerr效应和初始场强对辐射谱的影响.发现在光子数态的情况下,Kerr效应使低频峰增强、高频峰减弱,并使各峰向右移动.在初始腔场为较强的相干态时,原子辐射谱明显地分成两个拱形的梳状峰群,Kerr效应的增强使左侧峰群增高,右侧的边峰受到抑制.在压缩真空态情况下,边带峰只出现在中心频率双峰的左侧,随Kerr效应和初始场的增强,边峰个数也随之增多.无论哪种情况都破坏谱结构的对称性,在强场条件下Kerr效应的影响更加显著.     

Laser cooling of a nanomechanical resonator mode to its quantum ground state

We show that it is possible to cool a nanomechanical resonator mode to its ground state. The proposed technique is based on resonant laser excitation of a phonon sideband of an embedded quantum dot. The strength of the sideband coupling is determined directly by the difference between the electron-phonon couplings of the initial and final states of the quantum dot optical transition. Possible applications of this scheme include generation of nonclassical states of mechanical motion.     

The effect of surface temperature on H2/D2(v = 0, j = 0)–Ni(100) scattering processes

We carry out both four-dimensional (4D×2D) and six-dimensional (6D) quantum dynamics on a parametrically time- and temperature-dependent effective Hamiltonian for H₂/D₂(v = 0,j = 0)–Ni(100) collision process. Such an effective potential was derived within a theoretical framework of mean-field approximation by considering weakly correlated interaction between molecular degrees of freedom, phonon modes and electron– hole pair (elhp) coupling through a Hartree-product-type wave function, where the initial state distribution of the surface modes and elhp coupling were introduced through Bose– Einstein and Fermi– Dirac probability factor, respectively. The temperature-dependent dissociation and state-to-state transition probabilities for H₂/D₂(v = 0,j = 0)–Ni(100) system are depicted as a function of initial kinetic energ of the incoming diatom. Though such effect appears negligibly small for H₂(v = 0,j = 0)–Ni(100) system, it is prominent in the case of D₂(v = 0,j = 0)–Ni(100) collision. It appears that the change of dissociation and transition probabilities of D₂ with the increase of surface temperature is exclusively dictated by the phonon modes directed along Z-axis, but the effect of elhp coupling particularly for transition probabilities is insignificant.     

Eigenvalue problem for arbitrary linear combinations of a boson annihilation and creation operator

The eigenvalue problem for arbitrary linear combinations kα + μα^? of a boson annihilation operator α and a boson creation operator α^? is solved. It is shown that these operators possess nondegenerate eigenstates to arbitrary complex eigenvalues. The expansion of these eigenstates into the basic set of number states | n >, (n = 0, 1, 2, …), is found. The eigenstates are normalizable and are therefore states of a Hilbert space for | ζ | < 1 with ζ ? μ/k and represent in this case squeezed coherent states of minimal uncertainty product. They can be considered as states of a rigged Hilbert space for | ζ | ? 1. A completeness relation for these states is derived that generalizes the completeness relation for the coherent states | α 〉. Furthermore, it is shown that there exists a dual orthogonality in the entire set of these states and a connected dual completeness of the eigenstates on widely arbitrary paths over the complex plane of eigenvalues. This duality goes over into a selfduality of the eigenstates of the hermitian operators kα + k* α^? to real eigenvalues. The usually as nonexistent considered eigenstates of the boson creation operator α^? are obtained by a limiting procedure. They belong to the most singular case among the considered general class of eigenstates with ζ ? μ/k as a parameter.     

Multimode stimulated Raman scattering with squeezed light

Stimulated Raman scattering of a multimode pump light on an one-mode phonon system is examined. The pump light is expected to be strong, so that it can be treated classically. The phonon mode and scattered Stokes and anti-Stokes modes are described quantally. The phonon is prepared in a coherent state and the scattered modes are prepared in displaced and squeezed states at the input.The author would like to thank Dr. J. Peina for fruitful discussions, and Dr. A. Luk for comments on the results.