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Cavity modes for the single-cavity and the double-cavities in two-dimensional phononic crystal are studied by using a plane waves expansion supercell method. We show that the single-cavity behaves like an atom while the double-cavities behave like a molecule. Couplings of cavity modes with the waveguide modes are investigated for typical configurations. Suitably designed waveguides with introduced cavities might be used as acoustic filter in waveguide applications. 相似文献
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A. Loidl R. Feile K. Knorr B. Renker J. Daubert D. Durand J. B. Suck 《Zeitschrift für Physik B Condensed Matter》1980,38(3):253-262
TheE g andT 2g acoustic phonon modes of the molecular crystals KBr0.96(CN)0.04 and KBr0.86(CN)0.14 have been investigated by inelastic neutron scattering at 6, 90 and 300 K. Clear resonances due to mode-mode coupling to molecular excitations were observed. In complementary ultrasonic experiments the elastic constants were found to pass through minima as a function of temperature. The results were quantitavely explained by a model which assumes simple forms of the molecular excitation spectrum. An alternative interpretation, though being only qualitative, postulates a freezing of the CN molecules into a glass-like phase. 相似文献
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I. Abbasian Shojaei A. Soltani Vala S. Shojaei M. Kalafi 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(1):63-68
We present a detailed study of localized defect modes in finite two-dimensional magnetic photonic crystal consisting of cylindrical
ferrite material in air background by using the scattering matrix method. It is shown that due to having positive and negative
value of the effective magnetic permeability in interested photonic band gap, the defect modes present different behavior.
Our results show that the modes appeared in positive permeability region have features similar to the modes supported by the
dielectric photonic crystal while those created in the negative permeability region are strongly localized at the interface
of defect ferrite rod with air background. Moreover, results indicate that defect modes occurred in the negative region are
sharper than those appeared in the positive one which means the quality factor of former case is extremely high. 相似文献
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构建了一种简单的二维声子晶体:由两个横截面为三角形的钢柱所组成的复式元胞按三角点阵的形式排列在空气中,等效地形成了一个蜂巢点阵结构.当三角形钢柱的取向与三角点阵的高对称方向一致时,整个体系具有C_(6v)对称性.研究发现:在保持钢柱填充率不变的条件下,只需要将所有三角柱绕着自己的中心旋转180°,就可实现二重简并的p态和d态在布里渊区中心Γ点处的频率反转,且该能带反转过程实质上是一个拓扑相变过程.通过利用Γ点的P态和d态的空间旋转对称性,构造了一个赝时反演对称性,并在声学系统中实现了类似于电子系统中量子自旋霍尔效应的赝自旋态.随后通过k·p微扰法导出了Γ点附近的有效哈密顿量,并分别计算了拓扑平庸和非平庸系统的自旋陈数,揭示了能带反转和拓扑相变的内在联系.最后通过数值模拟演示了受到拓扑不变量保护的声波边界态的单向传输行为和对缺陷的背向散射抑制.文中所研究的声波体系,尽管材料普通常见,但其拓扑带隙的相对宽度超过21%,比已报道的类似体系的带隙都要宽,且工作原理涵盖从次声波到超声波的很大频率范围,从而在实际应用上具有较大的优势和潜力. 相似文献
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Kivshar YS 《Physical review. B, Condensed matter》1993,47(17):11167-11170
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The spatial distribution of the electromagnetic field in a two-dimensional photonic crystal with a lattice defect is investigated.
It is shown that in such a structure the field can be localized in a region smaller than one wavelength in size. The dependence
of the spectrum of defect modes on the parameters of a two-dimensional photonic crystal is investigated. The light field at
the exit of the photonic crystal possesses properties of a nonradiative mode, making it possible to achieve spatial resolution
in the near-field much higher than the radiation wavelength. The possibilities of using this phenomenon in optical near-field
microscopy to produce optical memory devices and to increase the efficiency of nonlinear optical interactions are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 323–328 (10 September 1999) 相似文献
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The structure of impurity excitations in solid binary solutions XeKr, XeAr, KrAr has been studied using the luminescence vacuum u.v. spectroscopy. Emission from biatomic heteronuclear molecules of inert elements was separated. The existence of two excited states of heteronuclear molecules of different atomic configurations is predicted. The pair potential of inert element interaction in the excited and ground states are analysed and force constants found. The peculiarities of the heteronuclear molecule formation as a function of concentration and temperature for solid binary solutions of inert gases have been discussed. 相似文献
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A. F. Bokhonov S. V. Davydov I. I. Kulak M. I. Nedel'ko L. A. Ogurtsova F. S. Pokrovskaya 《Journal of Applied Spectroscopy》1989,50(6):615-620
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 6, pp. 966–972, June, 1989. 相似文献
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The interaction between the rotational degrees of freedom of a diatomic impurity molecule and phonon excitations of a two-dimensional atomic matrix commensurate to the substrate is investigated theoretically. It is shown that the translational-rotational interaction leads to renormalization of the crystal field constants and a change in the form of the operator for the rotational kinetic energy as compared to the corresponding expression for a free rotator. The contribution from the rotational degrees of freedom of impurities to the low-temperature heat capacity of a diluted solution of diatomic molecules in the two-dimensional atomic matrix is calculated. The possibility of experimentally observing the predicted effects is discussed. 相似文献
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R.C. Newman 《物理学进展》2013,62(75):545-663
A brief account is given of the theory of the vibrations of an imperfect crystal containing isolated impurities and pairs of impurities, and the strength of the induced infra-red absorption is discussed. An analysis is then made, by the methods of group theory, of the energy levels and expected optical transitions of an anharmonic localized oscillator vibrating in a static potential well with various point symmetries. These results are compared with the available experimental data for pairs of impurities and more complicated impurity aggregates in ionic crystals with the fluorite and rocksalt structures, and also for similar defects in the covalent crystals silicon, germanium and some III–V compound materials. 相似文献
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Experiments quantifying the rotational and translational motion of particles in a dense, driven, 2D granular gas floating on an air table reveal that kinetic energy is divided equally between the two translational and one rotational degrees of freedom. This equipartition persists when the particle properties, confining pressure, packing density, or spatial ordering are changed. While the translational velocity distributions are the same for both large and small particles, the angular velocity distributions scale with the particle radius. The probability distributions of all particle velocities have approximately exponential tails. Additionally, we find that the system can be described with a granular Boyle's law with a van?der?Waals-like equation of state. These results demonstrate ways in which conventional statistical mechanics can unexpectedly apply to nonequilibrium systems. 相似文献
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《Physics letters. A》1998,237(3):175-182
Green's function methods are used to study H-polarized electromagnetic single site and waveguide impurity modes in two-dimensional photonic crystals. Modes for impurities formed of frequency independent, frequency dependent, and nonlinear dielectric media are treated. Results for H- and E-polarized modes are compared and contrasted. 相似文献
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We have derived an expression for the light scattering spectrum of a crystal in which the mechanically regular sites are occupied by point polarizable orientationally disordered molecules when the polarizabilities are assumed to depend on the positions of the surrounding atoms (interaction induced polarizability fluctuations). Owing to the ‘electrical’ disorder properties of the system all phonons can contribute to the anisotropic scattering measured in all polarization configuration with wavevector, branch index and polarization dependent coefficients. Assuming short range interaction induced polarizabilities we show that the temperature reduced intensity I(ω)/[n(ω) + 1] is given by a superposition of the Brillouin zone centre symmetry ‘projected’ density of states with polarization dependent coefficients. These coefficients are found to be essentially frequency independent for all the projections, exception made for those corresponding to the acoustic phonons. For the acoustic branches the coefficients vanish in a first approximation. They can however be treated on more rigorous grounds and, as already found by other authors, their contribution is proportional to the density of states multiplied by ω2. In addition zone centre (k?0) totally symmetric phonons can also be present in the ‘isotropic’ term (which appears only in the polarized VV configuration). A procedure is suggested to obtain the total density of states from the spectra measured in different polarization configurations. 相似文献