共查询到20条相似文献,搜索用时 9 毫秒
1.
A. Paolone P. Roy A. Pimenov A. Loidl A.A. Mukhin A.M. Balbashov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):245-250
The optical conductivity of La0.85Sr0.15MnO3 single crystals was studied by means of submillimeter and infrared spectroscopy for frequencies cm-1 and temperatures 10 K <
T
<300 K. The submillimeter conductivity follows the temperature dependence of the dc-data. The phonon spectrum of La0.85Sr0.15MnO3 changes considerably below K revealing a structural phase transition induced by charge or orbital order. At T
=10 K a number of phonon modes can be identified in addition to the room-temperature spectrum. The optical conductivity () in the mid-infrared reveals the characteristics of small polaron absorption. Below the magnetic ordering temperature the
polaron binding energy is highly reduced, but the onset of charge order interrupts the formation of free charge carriers with
a Drude-like behavior. The frequency and temperature dependence of in this regime qualitatively resembles the small polaron predictions by Millis et al. (Phys. Rev. B 54, 5405 (1996)).
Received 5 November 1999 相似文献
2.
M. Sassetti B. Kramer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):357-367
The Raman spectra of quantum wires in the region of electronic intra-band excitations are investigated using one- and two-band
models based on the Luttinger approximation with spin. Structures related to charge and spin density modes are identified,
and analyzed with respect to their behavior with photon energy and temperature. It is found that the low-energy peaks in the
polarized spectra, close to resonance that are commonly assigned to “single particle excitations”, can be interpreted as the
signature of spin density excitations. A broad structure in the resonant depolarized spectrum is predicted above the frequency
of the spin density excitations. This is due to simultaneous but independent propagation of spin and charge density modes.
The results, when compared with experiment, show, that the electronic collective excitations of quantum wires at low energies
are characteristic for a non-Fermi liquid.
Received: 25 March 1998 / Accepted: 3 June 1998 相似文献
3.
The BaW04-17 phase is synthesized at 5.0 GPa and 610~C with a cubic-anvil apparatus and identified by XRD. Raman scattering measurement is carried out to investigate the phase behaviour of a pure BaW04-Ⅱ phase (space group P21/n, Z = 8) under hydrostatic pressures up to 14.8 GPa at ambient temperature. In each spectrum recorded for this phase, 27 Raman modes are observed, and all bands shift toward higher wavenumber with a pressure dependence ranging from 3.8 to 0.2 cm- 1/GPa. No pressure-driven phase transition occurs in the entire pressure range in this study. Our results indicate that the previously reported high pressure phase of Ba WO4 at pressure above about 10 GPa and room temperature (Errandonea et al. Phys. Rev. B 73(2006)224103) is not the BaW04-Ⅱ phase. 相似文献
4.
E. Buixaderas S. Kamba J. Petzelt M. Savinov N.N. Kolpakova 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):9-16
The infrared reflectivity of Cd2Nb2O7 single crystal was studied in the temperature interval of 10-540 K, together with complementary dielectric measurements.
A ferroelectric soft mode was revealed above the ferroelectric phase transition at T
c = 196 K coupled with a central-mode type dispersion in the near-millimetre range. This proves the mixed displacive and order-disorder
nature of the transition. Below T
c many new modes were detected due to lowering of the symmetry, especially below the previously suggested incommensurate transition
at 85 K. Discussion of the possible phase transitions based on symmetry considerations is presented with the conclusion that
the ferroelectric transition is proper with the F1u symmetry of the order parameter, whereas the intermediate ferroelastic transition is improper and triggered by the coupling
with the ferroelectric order parameter.
Received 17 July 2000 相似文献
5.
T. Rudolf Ch. Kant F. Mayr M. Schmidt V. Tsurkan J. Deisenhofer A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(2):153-160
We studied the optical properties of antiferromagnetic ZnCr2Se4 by infrared spectroscopy up to 28,000 cm-1 and for temperatures from 5 to 295 K. At the magnetic phase transition at 21 K, one of the four phonon modes reveals a clear
splitting of 3 cm-1 as a result of spin-phonon coupling, the other three optical eigenmodes only show shifts of the eigenfrequencies. The antiferromagnetic
ordering and the concomitant splitting of the phonon mode can be suppressed in a magnetic field of 7 T. At higher energies
we observed a broad excitation band which is dominated by a two-peak-structure at about 18,000 cm-1 and 22,000 cm-1, respectively. These energies are in good agreement with the expected spin-allowed crystal-field transitions of the Cr3+ ions. The unexpected strength of these transitions with d-d character is attributed to a considerable hybridization of the
selenium p with the chromium d orbitals. 相似文献
6.
M. Sassetti F. Napoli B. Kramer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):643-654
Using the bosonization technique, a theory for the collective excitations of the interacting electrons in quantum wires with
two subbands occupied is developed. The dispersion relations for the inter-subband charge and spin density excitations are
determined. The results are used to interpret the features observed in recent measurements of the Raman spectra of AlGaAs/GaAs
quantum wires, particularly for photon energies near band gap resonance. It is shown that peaks previously identified as “single
particle excitations” are signatures of higher order collective spin density excitations. Predictions about the observability
of the interband modes are made.
Received 8 February 1999 相似文献
7.
Olga Degtyareva Viktor V. Struzhkin Russell J. Hemley 《Solid State Communications》2007,141(3):164-167
The vibrational dynamics of elemental solids that form incommensurate host-guest structures are of fundamental interest. High-pressure Raman scattering has been used to examine the vibrational spectrum of the group-V element Sb up to 33 GPa. A1g and Eg phonons of the ambient pressure rhombohedral A7 phase display a marked decrease with pressure, i.e., prior to the transition to the tetragonal host-guest Sb-II phase at 8.6 GPa, via the monoclinic host-guest Sb-IV phase. The Raman spectrum of the incommensurate host-guest Sb-II phase, has five bands between 80 cm−1 and 200 cm−1 that increase with pressure. For the bcc structure stable above 28 GPa, we observe one weak disorder-induced band that increases with pressure. 相似文献
8.
9.
R. Nemetschek R. Hackl M. Opel R. Philipp M.T. Béal-Monod J.B. Bieri K. Maki A. Erb E. Walker 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):495-503
After briefly recalling the d
+
s model valid for some anisotropic high T
c superconductors, we present a theory of electronic Raman spectra in that model and then compare it with new experimental
data obtained for an overdoped Y123 single crystal. The d
+
s model appears to describe satisfactorily the experimental results, indicating a possible doping dependence of the mixing
ratio. We note that the Raman spectrum of the overdoped Bi2212 could also be accounted for by the d
+
s superconductivity model. The case of Hg1212 (or Hg1223) is reexamined. It appears that the spontaneous breakdown of d-wave symmetry may be rather universal in high T
c cuprates.
Received: 3 March 1998 / Accepted: 30 April 1998 相似文献
10.
Haizheng Tao 《Solid State Communications》2006,137(8):408-412
Room temperature Raman scattering measurements of samples of the (1−x)GeS2-xIn2S3 (x=0.00-0.35) system have been conducted together with the FTIR transmission spectra of partial samples. Based on the Raman scattering and FTIR transmission spectra of the prepared defect spinel polycrystalline In2S3, the additional peaks at 306 and 245 cm−1 were ascribed to the local symmetric stretching vibration of InS4 tetrahedra and InS6 octahedra, respectively. According to the Raman scattering spectral evolution of the Ge-In sulfide glasses, the microstructure of the studied glasses was considered to be that S3Ge-GeS3 and S3In-InS3 ethane-like units originated from the sulfur deficient with the addition of In2S3 are homogeneously dispersed in a disordered polymer network formed by GeS4, InS4 tetrahedra and a small quantity of InS6 octahedra interconnected by sulfur bridges. 相似文献
11.
A. Sacchetti T. Corridoni E. Arcangeletti P. Postorino 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(3):301-305
We report a high-pressure Raman study on two members of the La1-xCaxMnO3-δ manganite family (x = 0.20, δ = 0 and δ = 0.08). The results obtained for the δ = 0 sample show a different behavior in
the low and high pressure regime which is ascribed to the onset of a new pressure-activated interaction previously invoked
in other manganite compounds. The comparison of our results with literature data gives further support to the identification
of the Jahn-Teller sensitive stretching mode and shows that pressure-induced octahedral symmetrization is more effective in
systems exhibiting a lower metallic character. On the contrary the new interaction sets in at a pressure which decreases on
increasing the metallic character of the system indicating an important role of the Mn–Mn hopping integral in its activation. 相似文献
12.
V. Mohaček-Grošev D. Kirin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):85-90
Methyl-mercury(II) halides CH3HgX (X = Cl, Br and I) were studied by means of temperature dependent Raman spectroscopy from 10 K to 410 K. In addition to
the previously reported soft phonons, new changes in the low frequency spectra were observed at T
≈ 70 K in CH3HgBr and at T
≈ 100 K in CH3HgI. The bandwidths of the two internal modes in CH3HgBr, the CH3 symmetric stretching band and the C-Hg-Br bending band, rise towards a local maximum at T
≈ 50 K as the temperature is raised from 10 K to 300 K. On the other hand the bandwidths of the two corresponding modes in CH3HgI crystals monotonously increase with temperature, obeying an Arrhenius law. Besides the three phonon modes present in the
Raman spectra of CH3HgCl at room temperature, the fourth phonon band that has been observed at temperatures below 245 K might correspond to the
freezing of methyl librations. The huge bandwidth of the C-Hg-Br bending mode could suggest the presence of additional weak
bonding of a mercury atom with bromine atoms from other molecules, thus inducing positional disorder.
Received 19 November 1999 and Received in final form 10 November 2000 相似文献
13.
H.L. Liu M.A. Quijada D.B. Tanner H. Berger G. Margaritondo 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):47-56
We report on the ab-plane polarized reflectance of an untwinned single crystal over the frequency range from 80 to (10 meV-4 eV) at temperatures between 10 and 300 K. We find a clear anisotropy in the ab-plane optical conductivity above and below , which is very similar to that formerly published data of (M.A. Quijada et al., Z. Phys. B 94, 255 (1994)). We employ both the one-component and two-component analyses to the optical data, which suggest that the normal-state
infrared anisotropy of originates not only from the mass anisotropy, but also from the scattering rate anisotropy. Our results provide evidence
that the electronic structures within the plane are anisotropic. In the superconducting state, there is a definite ab-plane anisotropy to the far-infrared absorption. This anisotropy could be due either to anisotropy of the superconducting
gap or to anisotropy of the mid-infrared component to the conductivity. We also observe the superconducting condensate is
anisotropic: The value of the superconducting penetration depth in the a-direction is slightly smaller than that along the b-axis.
Received 16 July 1998 相似文献
14.
L. Martín-Carrón A. de Andrés 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):11-16
We have studied the behavior of the Raman phonons of a stoichiometric LaMnO3 single crystal as a function of temperature in the range between 77 K and 900 K. We focus on the three main phonon peaks
of the Pbnm structure, related to the tilt, antisymmetric stretching (Jahn-Teller mode) and stretching modes of Mn-O octahedra.
The phonon frequencies show a strong softening that can be fit taking into account their renormalization because of three
phonon anharmonic effects in the pseudoharmonic approximation. Thermal expansion effects, in particular the variation of Mn-O
bond lengths with temperature, are not relevant above 300 K. On the contrary, phonon width behavior deviates from the three
phonon scattering processes well bellow T
c
. The correlation between the magnitude of the cooperative Jahn-Teller distortion, that disappears at 800 K, and the amplitude
of the Raman phonons in the orthorhombic phase is shown. Nevertheless, Pbnm phonons are still observable above this temperature.
Phonon width and intensity behavior around T
c
can be explained by local melting of the orbital order that begins quite below T
c
and by fluctuations of the regular Mn-O octahedra that correspond to dynamic Jahn-Teller distortions.
Received 25 January 2001 and Received in final form 14 March 2001 相似文献
15.
P.T. Jochym K. Parlinski M. Sternik 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):9-13
Ab initio calculations and a direct method have been applied to derive the phonon dispersion curves and phonon density of states for
the TiC crystal. The results are compared and found to be in a good agreement with the experimental neutron scattering data.
The force constants have been determined from the Hellmann-Feynman forces induced by atomic displacements in a supercell. The calculated phonon density of states suggests that vibrations of Ti atoms form acoustic branches, whereas the
motion of C atoms is confined to optic branches. The elastic constants have been found using the deformation method and compared
with the results obtained from acoustic phonon slopes.
Received 23 February 1998 相似文献
16.
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
17.
D. Zhang X. Chen Y. Jin X. Cao D. Zhu Y. Wang G. Ding Y. Cui C. Chen Z. Wu G. Lan 《Applied Physics A: Materials Science & Processing》2001,72(1):95-102
Raman spectra of Er:LiNbO3 crystal and Ti-diffusedEr:LiNbO3 strip waveguide, in which the Li/Nb ratio was altered using a vapor-phase equilibration (VPE) technique, were measured at
room temperature in the wave-number range 50–3500 cm-1. Both 488 and 514.5 nm radiations were used to excite Raman scattering, A1(TO) and E(TO) modes were recorded at backward scattering geometry. The results indicated that the lattice vibrational spectra
of the as-grown Er:LiNbO3 are almost the same as those of pure LiNbO3 except for the little shift of the peak position and the change of relative intensity of some peaks. In comparison with the
spectra of as-grown Er:LiNbO3 crystal the vapor-phase equilibrated Er:LiNbO3 and Er:Ti:LiNbO3 crystals in the lattice vibrational region exhibit the following features: firstly, Raman peaks become narrow, indicating
that the VPE process has brought Er:LiNbO3 and Er:Ti:LiNbO3 crystals closer to a stoichiometric composition; secondly, relative intensity of some peaks varies with the VPE time; and
finally, slight blue shifting in peak position was observed. Some of these features were correlated with the NbO6 octahedra and with the site distribution of the doped Er ions. In addition, green fluorescence peaks and/or bands associated
with the electron transitions 2
H
11/2?4
I
15/2 and 4
S
3/2?4
I
15/2 of the doped Er3+ were also observed. For 488 nm excitation they appear in the wavenumber range of 1200–3000 cm-1 and are well separated from lattice vibrational region; for 514.5 nm excitation, however, these fluorescence peaks shift
towards the low wavenumber region and overlap partially with the lattice vibrational spectra.
Received: 24 May 2000 / Accepted: 29 May 2000 / Published online: 13 September 2000 相似文献
18.
Yongqing Cai Litong Zhang Qingfeng Zeng Laifei Cheng Yongdong Xu 《Solid State Communications》2007,141(5):262-266
Using the linear response theory, vibrational and dielectric properties are calculated for c-BN, w-BN and h-BN. Calculations of the zone-center optical-mode frequencies (including LO-TO splittings) are reported. All optic modes are identified and excellent agreement is found between the theory and experimental results. The static dielectric tensor is decomposed into contributions arising from individual infrared-active phonon modes. It is found that all the structures have a smaller lattice dielectric constants than those of the electronic contributions. Finally, the infrared reflectance spectrums are presented. Our theoretical results indicate that w-BN shows a similar reflectivity spectrum as c-BN. It is difficult to tell apart the wurtzite structure from the zinc blende phase by IR spectroscopy. 相似文献
19.
J. Sichelschmidt M. Paraskevopoulos M. Brando R. Wehn D. Ivannikov F. Mayr K. Pucher J. Hemberger A. Pimenov H.-A. Krug von Nidda P. Lunkenheimer V.Yu. Ivanov A.A. Mukhin A.M. Balbashov A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):7-17
The charge-ordered perovskite Pr0.65Ca0.28Sr0.07MnO3 was investigated by means of magnetic susceptibility, specific heat, dielectric and optical spectroscopy and electron-spin
resonance techniques. Under moderate magnetic fields, the charge order melts yielding colossal magnetoresistance effects with
changes of the resistivity over eleven orders of magnitude. The optical conductivity is studied from audio frequencies far
into the visible spectral regime. Below the phonon modes hopping conductivity is detected. Beyond the phonon modes the optical
conductivity is explained by polaronic excitations out of a bound state. ESR techniques yield detailed informations on the
(H,T ) phase diagram and reveal a broadening of the linewidth which can be modeled in terms of activated polaron hopping.
Received 9 August 2000 相似文献
20.
Sonic stop-bands for cubic arrays of rigid inclusions in air 总被引:2,自引:0,他引:2
M.S. Kushwaha B. Djafari-Rouhani L. Dobrzynski J.O. Vasseur 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):155-161
Extensive band structures have been computed for cubic arrays of rigid spheres and cubes in air. Complete stop bands are obtained
for the face-centered-cubic (fcc) structure; however, there is no gap for the body-centered-cubic (bcc) and simple-cubic (sc)
structures. These gaps start opening up for a filling fraction of (27%) for spherical (cubic) inclusions and tend to increase with the filling fraction, exhibiting a maximum at the close-packing.
We also propose a tandem structure that allows the achievement of an ultrawideband filter for environmental or industrial
noise in the desired frequency range. This work is motivated by the recent experimental measurement of sound attenuation on
the sculpture, by Eusebio Sempere, exhibited at the Juan March Foundation in Madrid (Nature 378, 241 (1995)) and complements the corresponding theoretical work (Appl. Phys. Lett. 70, 3218 (1997)).
Received: 24 October 1997 / Revised: 1 December 1997 and 26 January 1998 / Accepted: 6 March 1998 相似文献