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1.
Third-harmonic generation during reflection of electromagnetic radiation from a thin superconducting film with a mixed d-and s-order parameter is studied theoretically. The dependence of the third harmonic intensity on the temperature and amplitude of an incident wave is calculated in the framework of the Ginzburg-Landau theory for superconductors with a two-component order parameter, and its behavior in the vicinity of transitions between phases with different symmetries is analyzed. It is shown, in particular, that the third harmonic intensity in the vicinity of the temperature corresponding to the d ? d + s phase transition substantially increases and is a nonanalytic function of the amplitude of the incident wave, while no singularity in the nonlinear response is observed for the d ? d + is transition. The linear reflection coefficient is found to be virtually insensitive to these phase transitions.  相似文献   

2.
The structure of unitary irreducible representations of the noncompact uq(2, 1) quantum algebra that are related to a negative discrete series is examined. With the aid of projection operators for the suq(2) subalgebra, a q analog of the Gelfand-Graev formulas is derived in the basis corresponding to the reduction uq(2, 1) → suq(2)×u(1). Projection operators for the suq(1, 1) subalgebra are employed to study the same representations for the reduction uq(2, 1) → u(1)×suq(1, 1). The matrix elements of the generators of the uq(2, 1) algebra are computed in this new basis. A general analytic expression for an element of the transformation brackets <U∣T>q between the bases associated with the above two reductions (the elements of this matrix are referred to as q Weyl coefficients) is obtained for a general case where the deformation parameter q is not equal to a root of unity. It is shown explicitly that, apart from a phase, the q Weyl coefficients coincide with the q Racah coefficients for the suq(2) quantum algebra.  相似文献   

3.
The wellknown derivation ofFresnel's formula for the reflection coefficient of a metal surface in the case of an oblique incident wave polarized parallel to the plane of incidence includes a mistake concerning the boundary conditions and neglecting the possibility of optical excitation of plasma waves. The right formula for this case is derived in the following paper byForstmann. The discussion of an approximate formula obtained by a simplified method leads in the case of vanishing reflectivity forΩ>Ω p to a real Brewster-angleα B . ForΩ<Ω p there exists another solution with a complex Brewster-angle, representing a surface wave in form of a Zenneck-wave. For large wave numbers and for light velocity ? electron velocity the dispersion formula for these surface waves is nearly identical with that obtained byRitchie andWagner, while for small wave numbers there is a great difference between these two formulas. In the middle region the frequenceΩ is nearlyΩ p /√2.  相似文献   

4.
Long-time polarization relaxation in the temperature range where PBSN-6 single crystals reside in the relaxor state was studied. An analysis of the time dependence of the permittivity ε′(t) performed at measuring frequencies from 1 Hz to 1 kHz in weak electric fields E0 showed that the relaxation (or freezing) times derived by extrapolating relations of the type ε′(t) ~ log(t/t0) and ε′(t) ~ exp{?[ln(t/t0)]β} range from 108 to 1011 min and depend substantially on the bias voltage applied to the sample. A study of the pattern of the dielectric response in moderate and strong infralow-frequency fields revealed that, after a sample was maintained under a bias lower than the coercive force, it no longer exhibited the additional anomalies in the amplitude dependences of the effective loss tangent taneff(E0) than were observed in a thermally recuperated sample.  相似文献   

5.
We derive an exact infinite set of coupled ordinary differential equations describing the evolution of the modes of the classical electromagnetic field inside an ideal cavity containing a thin slab with the time-dependent conductivity σ(t) and dielectric permittivity ε(t) for the dispersion-less media. We analyze this problem in connection with the attempts to simulate the so-called dynamical Casimir effect in three-dimensional electromagnetic cavities containing a thin semiconductor slab periodically illuminated by strong laser pulses. Therefore, we assume that functions σ(t) and δε(t) = ε(t) ? ε(0) are different from zero during short time intervals (pulses) only. Our main goal here is to find the conditions under which the initial nonzero classical field could be amplified after a single pulse (or a series of pulses). We obtain approximate solutions to the dynamical equations in the cases of “small” and “big” maximal values of the functions σ(t) and δε(t). We show that the single-mode approximation used in the previous studies can be justified in the case of “small” perturbations, but the initially excited field mode cannot be amplified in this case if the laser pulses generate free carriers inside the slab. The amplification could be possible, in principle, for extremely high maximum values of conductivity and the concentration of free carries (the model of an “almost ideal conductor”) created inside the slab under the crucial condition providing the negativity of the function δε(t). This result follows from a simple approximate analytical solution confirmed by exact numerical calculations. However, the evaluation shows that the necessary energy of laser pulses must be, probably, unrealistically high.  相似文献   

6.
The optical properties of Violet 1-doped polyvinyl alcohol (PVA) have been investigated using Wemble and Didomenico (WD) method. The optical constants such as refractive index n, the dispersion energy E d, the oscillation energy E 0, the lattice dielectric constant \(\varepsilon _{\infty } \), light frequency dielectric constant ε 0 and the ratio of carrier concentration to the effective mass N/m* have been determined using reflection spectra in the wavelength range 300–900 nm. The single- beam Z-scan technique was used to determine the nonlinear optical properties of Violet 1:polyvinylalcohol (PVA) thin film. The experiments were performed using continuous wave (cw) laser with a wavelength of 635 nm. The calculated nonlinear refractive index of the film, n 2 = ?2.79×10?7 cm2/W and nonlinear absorption coefficient, β = 6.31×10?3 cm /W. Optical limiting characteristics of the dye-doped polymer film was studied. The result reveals that Violet 1 can be a promising material for optical limiting applications.  相似文献   

7.
The dielectric properties of the triglycine sulfate (TGS) crystal grown by lowering the temperature with a transition through Curie point TC during its growth are studied. The greatest values of low-frequency dielectric permittivity εmax(T = TC) and effective dielectric permittivity εeff(E0) correspond to the layer of crystal formed at the temperature of the phase transition.  相似文献   

8.
The spin and lattice dynamics of the R2CuO4 quasi-2D antiferromagnetic crystals (R=Pr, Nd, Sm, Eu, Gd) were studied in the millimeter-range electromagnetic wave band. Strong variations of the absorption coefficient were observed to occur at temperatures TT0. Absorption lines of electrical nature due to lattice dynamics were also revealed near the T0 temperatures. The observed anomalies are assumed to originate from phase transitions at TT0, which entail changes in the structural and magnetic properties.  相似文献   

9.
The spectrum of spin fluctuations in the stacked-triangular antiferromagnet YMnO3 was studied above the Néel temperature using both unpolarized and polarized inelastic neutron scattering. We find an in-plane and an out-of-plane excitation. The in-plane mode has two components just above T N : a resolution-limited central peak and a Debye-like contribution. The quasi-elastic fluctuations have a line width that increases with q as Dq z and the dynamical exponent z = 2.3. The out-of-plane fluctuations have a gap at the magnetic zone center and do not show any appreciable q dependence at small wave vectors.  相似文献   

10.
The dimension D of a polycrystalline film and the optical anisotropy m = εzx of uniaxial crystallites with the principal components εx = εy and εz of the tensor of the dielectric constant have been shown to produce a strong influence on the effective dielectric constant εD* and the effective refractive index nD* = (εD*)1/2 of the film in the optical transparency region, as well as on the boundaries of the intervals BDl ≤ εD*BDu. The intervals Δ2(m) = B2lB2u and Δ3(m) = B3lB3u are separated by a gap for m in the range 1 < m < 2, whereas the theoretical dependence ε2*(m) is separated by a gap from the interval Δ3(m) for m in the range 1 < m < 4. This is confirmed by a comparison of the experimental (noP) and theoretical (nD*) ordinary refractive indices for uniaxial polycrystalline films of the conjugated polymer poly(p-phenylene vinylene) (PPV) with uniaxial crystallites and appropriate values of m. In the visible transparency region of the PPV films with a change in m(λ) in the range 2 < m(λ) < 3 due to the dependence of the components εx,z(λ) on the light wavelength λ, the refractive indices noP2(λ) = εoP(λ) are consistent with the theoretical values of ε2*(λ) and lie outside the interval Δ3(m). For m(λ) > 3 near the electronic absorption band of the crystallites, the values of εoP(λ) lie in the region of the overlap of the intervals Δ2(m) and Δ3(m). The boundaries mc of the range 1 < m < mc are determined, for which the interval Δ2(m) is separated by a gap from the dependences ε3*(m) corresponding to the effective medium theory with spherical crystallites and hierarchical models of a polycrystal, as well as from the proposed new dependence ε3*(m).  相似文献   

11.
Hamaker interaction energies and cutoff distances have been calculated for disordered carbon films, in contact with purely dispersive (diiodomethane) or polar (water) liquids, using their experimental dielectric functions ε (q, ω) obtained over a broad energy range. In contrast with previous works, a q-averaged <ε (q, ω) >  q is derived from photoelectron energy-loss spectroscopy (XPS-PEELS) where the energy loss function (ELF) < Im[?1/ε (q, ω)] >  q is a weighted average over allowed transferred wave vector values, q, given by the physics of bulk plasmon excitation. For microcrystalline diamond and amorphous carbon films with a wide range of (sp3/sp2 + sp3) hybridization, non-retarded Hamaker energies, A 132 (L < 1 nm), were calculated in several configurations, and distance and wavenumber cutoff values were then calculated based on A 132 and the dispersive work of adhesion obtained from contact angles. A geometric average approximation, H 0?CVL ?=?(H 0?CVC H 0?LVL )1/2, holds for the cutoff separation distances obtained for carbon-vacuum-liquid (CVL), carbon-vacuum-carbon (CVC) and liquid-vacuum-liquid (LVL) equilibrium configurations. The linear dependence found for A CVL, A CLC and A CLV values as a function of A CVC, for each liquid, allows predictive relationships for Hamaker energies (in any configuration) using experimental determination of the dispersive component of the surface tension, \( {\gamma}_{CV}^d \), and a guess value of the cutoff distance H 0?CVC of the solid.
Graphical Abstract
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12.
This paper reports on an experimental and theoretical study of the spectra of Bragg reflection of light from opal-like photonic crystals near the critical angle of incidence ? c , at which the Bragg reflection in the p polarization of reflected light disappears The objects studied were polymer photonic-crystal structures made up of polystyrene particles. It is shown that Bragg reflection for the electromagnetic TM mode becomes totally suppressed at an angle of incidence ? c , which depends on the geometric parameters and dielectric constants of the spatially periodic structure.  相似文献   

13.
The uniaxial strain of quasi-one-dimensional conductor whiskers of orthorhombic TaS3 at a strain higher than ε c ~ 0.8% leads to a sharp increase in the coherence of the properties of a charge density wave (CDW), which manifests itself in its motion in fields higher than threshold field E t . During uniaxial elongation, TaS3 is shown to exhibit the following unusual properties even in weak fields: Peierls transition temperature T P depends nonmonotonically on ε, one-dimensional fluctuations weaken near T P , and the coherence length of a charge density increases at T < T P . Investigations in fields higher than E t show that the ultracoherent properties of CDW exist in a wide temperature range and are retained when temperature increases up to T P . These properties of CDW make it possible to observe a sharp increase in E t near T P and an almost jumplike increase in E t at T < 90 K. The increase in E t at T P is explained by a decrease in the coherence volume of CDW because of a fluctuational suppression of the Peierls gap.  相似文献   

14.
A discussion of the Born-Huang theory of dispersion in polar crystals with regard to the internal vibrations of molecular crystals (organic crystals, ionic crystals with complex ions) connects the imaginary part (?″) of the optical dielectric tensor (?)=(?′)?i(?″) with the eigenfrequencies of the vibrations active in absorption and with the direction and magnitude of the transition moments in crystals. The limits are shown, within which this theory gives a Lorentzian line shape, often found in experiment. The propagation of an electromagnetic wave in a strongly absorbing, anisotropic medium and its reflection at crystal boundaries are investigated with special emphasis on the experimental determination of (?). This treatment leads to expressions for (?), which are not limited to the case of weak absorption and which are valid for all crystal symmetries.  相似文献   

15.
The evolution of the surface morphology of LPCVD poly-Si films (deposition temperature 620°C), a-Si films (deposition temperature 550°C) and poly-Si films, obtained by the crystallization of a-Si is investigated in the thickness range 40–500 nm. It is found that upon an increase in the thickness from 40 to 500 nm, the surface roughness (parameters S q , S z , S v ) is increased for poly-Si, while in the case of a-Si and poly-Si obtained by crystallization a-Si, on the contrary, decreases. The correlation length (S al ) increases for all three types of silicon films. Poly-Si films, obtained by the crystallization of a-Si, as compared to LPCVD poly-Si films have a significantly lower surface roughness, respectively, S q two times less at a thickness of 40 nm and sixteen times less at 500 nm. In contrast to thick films, thin a-Si films (at thicknesses of less than 40 nm) have a granular structure, which is especially pronounced at an average thickness of about 20 nm and there is a maximum on the dependence of the roughness S q on the thickness.  相似文献   

16.
Spatial nonlocality (dispersion) of transport equations leads to a nonlinear dependence of the voltage drop U on the distance between the points of voltage measurement. For this reason, the results of conventional two-probe measurements of conductivity substantially depend on the relationship between the linear dimensions of the sample L and the characteristic length of spatial dispersion R of the generalized diffusion coefficient D(q, ω). This makes it possible to obtain information on the character of spatial nonlocality of D(q, ω) in the vicinity of the Anderson transition and, in particular, on the magnitude of the correlation multifractal dimension D2 of electron wave functions near the mobility edge.  相似文献   

17.
The dynamics of charge carriers in doped graphene, i.e., graphene with a gap in the energy spectrum depending on the substrate, in the presence of a Coulomb impurity with charge Z is considered within the effective two-dimensional Dirac equation. The wave functions of carriers with conserved angular momentum J = M + 1/2 are determined for a Coulomb potential modified at small distances. This case, just as any two-dimensional physical system, admits both integer and half-integer quantization of the orbital angular momentum in plane, M = 0, ±1, ±2, …. For J = 0, ±1/2, ±1, critical values of the effective charge Zcr(J, n) are calculated for which a level with angular momentum J and radial quantum numbers n = 0 and n = 1 reaches the upper boundary of the valence band. For Z < Zcr (J, n = 0), the energy of a level is presented as a function of charge Z for the lowest values of orbital angular momentum M, the level with J = 0 being the first to descend to the band edge. For Z>Zcr (J, n = 0), scattering phases are calculated as a function of hole energy for several values of supercriticality, as well as the positions ε0 and widths γ of quasistationary states as a function of supercriticality. The values of ε0* and width γ* are pointed out for which quasidiscrete levels may show up as Breit–Wigner resonances in the scattering of holes by a supercritical impurity. Since the phases are real, the partial scattering matrix is unitary, so that the radial Dirac equation is consistent even for Z > Zcr. In this single-particle approximation, there is no spontaneous creation of electron–hole pairs, and the impurity charge cannot be screened by this mechanism.  相似文献   

18.
Polarized spectra of reflectance R(ν) and transmittance Tr(ν) of single-crystal CdTiO3 samples have been obtained in the frequency range 7 < ν < 1000 cm?1 and for temperatures from 5 to 300 K using IR Fourier spectroscopy and submillimeter-range techniques. Dispersion analysis was carried out in terms of the additive-oscillator model, and dielectric responses ε(ν) and ε″(ν) were calculated. The polar modes were assigned to particular symmetry types, and their oscillator parameters (dielectric contributions, normal frequencies, damping constants) were determined. The numerical values of the components of the static permittivity tensor, ε11 and ε33, are shown to be almost fully determined by the total dielectric contributions due to the B3u and B1u phonons, respectively. In the low-frequency domain, lines showing anomalous behavior of the oscillator parameters, which is characteristic of soft ferroelectric modes, were observed. It is shown that, in CdTiO3 at cryogenic temperatures, there exist several different polar states with switching in the direction of the spontaneous polarization vector.  相似文献   

19.
The infrared reflection spectra of mechanically free and uniaxially compressed LiNH4SO4 crystals are studied for the first time in the spectral range of 800–1700 сm–1 along three crystallophysical directions. The Kramers–Kronig dispersion relations are used to determine the dispersion and baric dependences of refractive index n and the real ε1 and imaginary ε2 parts of the dielectric constant and to calculate the frequencies of longitudinal ωLO and transverse ωТO vibrations, decay constant γ, and oscillator strength f of mechanically free and compressed LiNH4SO4 crystals. The considerable changes observed in the main reflection bands are explained by the effect of uniaxial pressures on the NH4 and SO4 tetrahedra.  相似文献   

20.
In this paper, we first construct the Cauchy q-shift operator T(a, b;D xy ) and the Cauchy q-difference operator L(a, b; θ xy ). We then apply these operators in order to represent and investigate some new families of q-polynomials which are defined in this paper. We derive some q-identities such as generating functions, symmetry properties and Rogers-type formulas for these q-polynomials. We also give an application for the q-exponential operator R(bD q ).  相似文献   

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