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1.
O. Dubos W. Petry J. Neuhaus B. Hennion 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):447-454
We present inelastic neutron scattering measurements of the low energy and strongly damped phonons in the high temperature
bcc phase of zirconium. These phonons were investigated at different scattering vectors but equivalent phonon wave vectors in different Brillouin zones or along different but equivalent paths in the same Brillouin zone. Neither the observed differences
in intensity nor in line shapes can be explained by the coherent one-phonon scattering law . This leads to an apparent violation of the fundamental symmetry of lattice dynamics. Taking into account the strong anharmonicity
of these phonons, interferences between one- and multi-phonon scattering are held responsible for these effects. Measurements
in different scattering planes reveal that due to the symmetry of the bcc lattice, these effects can only be observed in certain
directions.
Received: 24 December 1997 / Received in final form: 9 March 1998 / Accepted: 19 March 1998 相似文献
2.
Using the model of rigid ions bound by short-distance forces the lattice dynamics of the CuA1S2 crystal with chalcopyrites structure are investigated. The model parameters are determined from experiments on infrared reflection and combination scattering of light. The phonon spectrum is calculated in the center of the Brillouin zone and in directions of high symmetry. Oscillator amplitudes for frequencies active in IR reflection and components of the static dielectric permeability tensor are calculated. 相似文献
3.
We investigate the possibility of inducing ferromagnetic order in
4d and 5d late transition metals through crystal symmetry change.
First principles, self-consistent density functional theory
calculations, with spin-orbit coupling included, performed at 0 K
show that ferromagnetism occurs in the bulk of Rh and Pd at the
optimum lattice constant if Rh is in the bcc and Pd in the
hcp/dhcp phase. The ferromagnetic order originates in the d-band
occupancy of Rh or Pd which locates the Fermi energy at the top of
the highest peak of the respective (paramagnetic) density of
states induced by the bcc or hcp/dhcp structure. This peak in the
density of states is caused by flat bands which lie at the surface
of the respective Brillouin zone. For a bcc crystal these flat
bands have the eg character and are positioned at the surface
of the bcc Brillouin zone along the N-P line. The origin of the
flatness of the bands was found to be the translation symmetry of
the cubic lattice which causes the bands with the eg character
to be narrow along the k-lines whose k-vector directions are
furthest off the directions to which the orbitals of the eg
symmetry point. Due to the d-band occupancy of Rh these flat
bands lie in the paramagnetic state at the Fermi energy, whereas
in the ferromagnetic state they exhibit the largest
energetic split. This indicates that a smaller degree of orbital overlap
narrows electronic bands enhancing the tendency of the system for
ferromagnetic band split. For the hcp/dhcp structure the states
contributing to the high density of para-magnetic states at
the Fermi level of Pd lie in the vicinity of the M-L line
of the hcp Brillouin zone boundary, which possesses a high number
of symmetry (M and L) points. Moreover, the M-L line is aligned
with the stacking sequence direction ([0001]) which is furthest
off the densest-packed atomic chain direction of an hcp-crystal
and, consequently, the weakest-bond direction in the crystal. This
makes the narrow bands along the M-L line flat. The instability of
the bcc and the meta-stability of the hcp crystal phase
modifications for metals with native close-packed crystal
structures is subsequently analysed in order to find whether they
can be grown as films on suitable substrates. 相似文献
4.
M. Vos V.A. Sashin C. Bowles A.S. Kheifets E. Weigold 《Journal of Physics and Chemistry of Solids》2004,65(12):2035-2039
Electron momentum spectroscopy is often used to determine the spectral function of materials. It relies on the determination of the scattering angle of electrons with extremely high precision. In practice, it is important to calibrate these angles, and hence the momentum scales. Here we describe a method to do so and show how minor misalignments affect the measured momentum densities of Li2O. Using the same procedure we further calibrated the momentum scale by measuring the spectral momentum density along a Brillouin zone boundary of a Si single crystal. 相似文献
5.
M. Samsel-Czekała G. Kontrym-Sznajd G. Döring W. Schülke J. Kwiatkowska F. Maniawski S. Kaprzyk A. Bansil 《Applied Physics A: Materials Science & Processing》2003,77(1):87-92
A reconstruction technique based on the solution of the Radon transform in terms of Jacobi polynomials is used to obtain the
3D electron momentum density, ϱ(p), from nine high-resolution Compton profiles (CPs) for a Cu0.9Al0.1 disordered alloy single crystal. The method was also applied to theoretical CPs computed within the Korringa–Kohn–Rostoker
coherent potential approximation (KKR-CPA) first-principles scheme for the same nine orientations of the crystal. The experimental
ϱ(p) is in satisfactory agreement with the theoretical ϱ(p), shows most details of the Fermi surface (FS) and exhibits electron correlation effects. We comment on the map of the FS
obtained by folding the reconstructed ϱ(p) into the first Brillouin zone, which yields the occupation number density, ϱ(k). A test of the validity of data via a consistency condition (within our reconstruction algorithm) as well as the propagation
of experimental noise in the reconstruction of both ϱ(p) and ϱ(k) are investigated.
Received: 24 October 2001 / Accepted: 20 January 2002 / Published online: 3 June 2002
RID="*"
ID="*"Corresponding author. Fax: +48-71/344-10-29, E-mail: samsel@int.pan.wroc.pl 相似文献
6.
Angle-resolved photoemission measurements have been made on the metallic layer compound 2H-NbSe2. From the results, E vs k∥ dispersion curves have been obtained along two principal symmetry directions in the Brillouin zone. The experimental energy bands are found to be in good agreement with the results predicted by one-dimensional density of initial states along k⊥. 相似文献
7.
First principles calculations, by means of the full-potential linearized augmented plane wave method within the local density approximation, were carried out for the electronic properties of Li3GaN2. The calculated lattice parameter is in good agreement with the measured one. The bandgap is direct at the Brillouin zone centre. The Li-N and Ga-N bonds are both ionic with a small covalent character of the latter one. 相似文献
8.
结合均匀光子晶格的衍射关系和晶格中正负缺陷的布里渊区谱特性,探讨了光诱导二维光子晶格中线性缺陷模式的形成条件,对布里渊区中各点的缺陷模式进行了模拟分析,并得到了光子带隙结构中“嵌入点”X1点的正、负缺陷模式.结果表明:对于二维缺陷,只有当衍射关系曲面中沿两个正交的横向波矢方向同时为正常(反常)衍射的区域才能存在正(负)缺陷模式;而对于一维缺陷,只要在一个横向波矢方向上存在正常(反常)衍射的区域就可以支持正(负)缺陷模式,因此在某些特殊点处,正和负的缺陷模式可以同时存在.X1点正缺陷模式的存在预示着自聚焦非线性同样可以支持带内孤子.研究结果有助于对光子晶格中晶格孤子(特别是带内孤子)的理解和进一步研究.
关键词:
光诱导光子晶格
光子带隙
线性缺陷态 相似文献
9.
Yu. M. Basalaev P. V. Demushin E. V. Nikolaeva A. V. Silinin 《Moscow University Physics Bulletin》2011,66(1):39-44
It is demonstrated that the crystalline structure of MgGeN2 can be reduced to the superposition of “approximated” high-symmetry Bravais sublattices by shifting atoms in a unit cell
within the range of 5% of the lattice constant. The superimposed Brillouin zones were plotted for crystal lattices and sublattices.
The computational results are presented for the electronic structure of MgGeN2 in terms of the theory of the density function. The influence of “hidden” symmetry in this crystal on zone spectra is described. 相似文献
10.
V. I. Zinenko M. S. Pavlovskii A. S. Krylov I. A. Gudim E. V. Eremin 《Journal of Experimental and Theoretical Physics》2013,117(6):1032-1041
Raman spectra of light are obtained for HoFe3(BO3)4 and HoAl3(BO3)4 crystals at various temperatures and are used for determining the frequencies of crystal lattice vibrations at the center of the Brillouin zone. It is also found that the HoFe3(BO3)4 crystal exhibits a phase transition at T c ≈ 366 K. The magnetoelectric effect in the paramagnetic phase of these compounds is studied experimentally. The lattice vibration frequencies, elastic and piezoelectric moduli, Born dynamic charges, and the high-frequency permittivity are calculated using the density functional method. A peculiar behavior of the transverse acoustic vibration branch is observed in the Γ → Z direction of the Brillouin zone of the HoFe3(BO3)4 crystal. The electric polarization induced by an external field is estimated using the calculated values of piezoelectric moduli and experimental values of magnetostriction. 相似文献
11.
L. Liu J.T. Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):381-388
For photons propagating in a periodic dielectric lattice, the dispersion curve forms photonic bands separated by forbidden
gaps. When the dielectric lattice deviates only slightly from being homogenous, the photonic band structure resembles the
linear dispersion relation for photons folded into the first Brillouin zone, i.e., the so-called empty lattice bands. Using group theoretical technique, we calculate the splitting of the accidental degeneracies
in the empty lattice bands at symmetry points for a simple cubic dielectric lattice.
Received 23 June 1998 相似文献
12.
Bahadir Altintas 《Journal of Physics and Chemistry of Solids》2011,72(11):1325-1329
Transition metal based monosilicide compounds (CrSi and RhSi) have been investigated theoretically from ab initio calculations. The structural and electronic band calculations of CrSi and different phases of RhSi crystals show that the metallic property and hypothetically constructed structures of RhSi(Pnma) under different pressures from 0 GPa to 75 GPa show a certain difference only along Γ–Z directions of the high symmetry points of first Brillouin zone. The character of the bands around fermi level was determined by partial density of state calculations. 相似文献
13.
H. Salehi M. Aryadoust M. Zargar Shoushtari 《Applied Physics A: Materials Science & Processing》2014,116(1):69-77
In this paper, the propagation of acoustic waves in the phononic crystal of 3D with rhombohedral(I) lattice is studied theoretically. The crystal composite constituted of nickel spheres embedded in epoxy. The calculations of the band structure and density of states are performed with the plane wave expansion method in the irreducible part of Brillouin zone. In the present work, we have investigated the effect of lattice angle on the band structure and width of the band gap rhombohedral(I) lattice in the irreducible part of the first Brillouin zone and its planes separately. The results show that more than one complete band gape are formed in the four planes of the irreducible part. The most complete band gaps are formed in the (111) plane and the widest complete band gap in (443) with an angle greater than 80 \(^{\circ }\) . So, if the sound passes through the (111) and (443) planes for the lattice angle close to 90 \(^{\circ }\) , the crystal phononic displays the excellent insulation behavior. Moreover, in the other planes, the lattice angle does not affect on the width and the number of band gaps. Also, for the filling fraction 5 %, the widest complete band gap is formed. These results are consistent with the effect of symmetry on the band gap width, because the (111) plane has the most symmetry. 相似文献
14.
Cihan Parlak 《Physica B: Condensed Matter》2012,407(13):2622-2625
We report a detailed ab initio study of the structural, electronic, and volume dependent elastic and lattice dynamical properties of Sr(Ni0.5Si0.5)2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. The phonon dispersion curves along the high-symmetry directions and phonon frequencies with their Grüneisen parameters at the Brillouin zone center are computed by using density functional perturbation theory while the elastic constants are calculated in metric-tensor formulation. The band structure, and partial densities of states and Fermi surface topology are also discussed. 相似文献
15.
We present a detailed study of high Miller-index (h k l) photonic bands in a-SiO2 synthetic opals. Polarized light transmission spectra of opals were studied in a wide wavelength range for all high symmetry directions on the Brillouin zone (BZ) in the face-centered cubic (fcc) lattice. It is shown that under the conditions of low dielectric contrast the dispersion of high Miller-index photonic bands is described well by the calculated dependences of Bragg wavelengths diffracted from the (h k l) crystallographic planes of the fcc lattice. 相似文献
16.
Using the methods of the theory of charged corepresentation, the laws of dispersion were studied in the vicinity of symmetry points in the Brillouin zone for class D2d crystals which form the simple tetragonal lattice Γq. Possible variants from the dispersion laws were obtained by quadratic approximation of the parametric expansion of the wave-vector components, taking into consideration and neglecting spin-orbit coupling. The zero inclination points were determined. 相似文献
17.
Using the method of charged corepresentations [1], we obtain parametric expansions of dispersion laws in wave vector components in the quadratic approximation, possible degeneracies, and vanishing slopes of energy surfaces close to symmetry points of the Brillouin zone of class C4h crystals with a simple tetragonal lattice. 相似文献
18.
The structural and electronic properties of sodium bromide (NaBr) are investigated by the density functional theory (DFT) within the generalized gradient approximation (GGA) for the exchange and correlation energy. The equilibrium lattice constant, bulk modulus and its pressure derivative are obtained by fitting the calculated total energy to the third-order Birch-Murnaghan equation of state. The band structure along the higher symmetry axes in the Brillouin zone, the density of states (DOS) and the partial density of states (PDOS) are presented. The results have been discussed and compared with the available experimental and theoretical data. 相似文献
19.
Tacchi S Montoncello F Madami M Gubbiotti G Carlotti G Giovannini L Zivieri R Nizzoli F Jain S Adeyeye AO Singh N 《Physical review letters》2011,107(12):127204
The dispersion curves of collective spin-wave excitations in a magnonic crystal consisting of a square array of interacting saturated nanodisks have been measured by Brillouin light scattering along the four principal directions of the first Brillouin zone. The experimental data are successfully compared to calculations of the band diagram and of the Brillouin light scattering cross section, performed through the dynamical matrix method extended to include the dipolar interaction between the disks. We found that the fourfold symmetry of the geometrical lattice is reduced by the application of the external field and therefore equivalent directions of the first Brillouin zone are characterized by different dispersion relations of collective spin waves. The dispersion relations are explained through the introduction of a bidimensional effective wave vector that characterizes each mode in this magnonic metamaterial. 相似文献
20.
T. McAvoy J. Zhang C. Waldfried D.N. McIlroy P.A. Dowben O. Zeybek T. Bertrams S.D. Barrett 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):747-755
The experimental band structure of Mo(112) and the effects by temperature and adsorbate are presented. A surface resonance,
identified as crossing the Fermi level at about 1/3 from to of surface Brillouin zone, was observed to be very sensitive to both contamination and temperature. We find evidence of adsorbate
and temperature induced reconstruction of the Mo(112) surface. Examination of low-energy electron diffraction (LEED) and scanning
tunneling microscopy (STM) data provides evidence for an adsorbate induced reconstruction of the Mo(112) surface with periodicities
consistent with the Fermi level crossing of the surface resonance. The reconstruction is found to occur at coverages as low
as 0.03 Langmuirs of oxygen or carbon. The reconstruction and/or adsorbate affects the density of states and bands near the
Fermi level of a
1 symmetry.
Received 3 March 1999 and Received in final form 1 October 1999 相似文献