Phonon Raman scattering in (La1−xSrx)2CuO4single crystals (original) (raw)
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Investigation of electron–phonon interaction in La2−xSrxCuO4 by Raman scattering
Physica B: Condensed Matter, 1999
In this paper, the problem of electron-phonon interaction (EPI) in semiconductor crystals and quantum dots (QDs) is considered. It is shown that the model of strong EPI developed for organic molecular crystals can be successfully applied to bulk and nanosized semiconductors. The idea of the approach proposed here is to describe the experimental Raman (or absorption) spectra containing the phonon replicas theoretically by varying the EPI constant. The main parameter of the theoretical expression describing the experimental spectrum is the ratio of EPI constant to the frequency of the corresponding phonon mode. Based on the experimental and theoretical results, we have found that decreasing the size of CdS x Se 1-x QDs embedded in borosilicate glass matrix results in some enhancement of electron-phonon interaction.
Electron-phonon interaction in La 2 − x Sr x CuO 4 investigated by Raman scattering
Physical Review B, 2000
Using high-quality single crystals of La 2Ϫx Sr x CuO 4 , Raman scattering spectra in the ͑c,c͒ geometry have been investigated in different Sr concentrations (xϭ0,0.1,0.113,0,15,0.22) and in the wide temperature region. It has been found that the apical oxygen vibration along the c axis shows the following anomalous behaviors in the dependences of the Sr concentration and temperature. With the increase of the Sr concentration, the peak intensity abruptly decreases from xϭ0 to 0.1 and its line shape becomes asymmetric. In the temperature dependence, its energy is almost constant or slightly decreases with decreasing temperature, and also its intensity decreases above 100 K universally in the doped samples. In addition, the background intensities increase with increasing x, except for xϭ0.113 at 6 K, where ''1/8 problem'' occurs. This increase shows that the background response is caused by an electronic excitation because the magnetic one is forbidden in the ͑c,c͒ spectra. The decrease of the background at xϭ0.113 at 6 K is understood by the formation of charge density wave. The asymmetric line shapes of the apical oxygen vibration are well explained by the Fano model, which is based on the interference effect between the phonon and electronic excitations. Furthermore, the abrupt decrease of the intensity from xϭ0 to 0.1 is also explained by the introduction of the electron-phonon interaction. The correlation between the obtained electron-phonon interaction and T c has been found in the Sr-concentration dependence.
Infrared spectra of optical phonons in semiconducting La2CuO4+x single crystals
Physica C: Superconductivity, 1993
Far-infrared mfl~ivity spectra R(~) in polarization E.I_ C and DC-conductivity ape have been studied in a semieonducting phase of La2CuO4+x single crystals with various oxygen contents. The spectrum of infrared-active optical phonons has been obtained for stoiehiometric La2CuO4. It has been shown that the phonon spectrum should be analyzed in a framework of the orthorhombie crystal structure at T< 300 IC Extra lines have been found in the phonon spectrum upon doping the crystals with oxygen. The results of studying the temperature dependence of R(~) and a~c allow one to interpret these features as vibrational modes, which are active in the l~arnao scattering spectrum and displayed in the IR spectrum due to their interaction with selflocalized holes.
Journal of Raman Spectroscopy, 2009
The Raman scattering spectra of uranium-doped Ca2CuO3 were investigated. The small doping of uranium (≤5%) in this one-dimensional spin 1/2 chain system induced three new first-order scattering bands and two new multiphonon bands in the structure of forbidden phonons. The first-order bands were found to agree well with the existing theoretical results from the ab initio and tight-binding calculation. Among them, the 470 and 665 cm−1 bands appeared as the basic wavenumbers of which the multiphonon overtones were composed. The grain size effect in this strongly anisotropic system was proposed not to originate from the classical phonon confinement but rather as a result of the segmentation of one-dimensional spin chains due to doping, which in turn allowed the new vibrational modes and implied the appearance of higher overtones in the scattering spectra. Copyright © 2008 John Wiley & Sons, Ltd.
Symmetry of phonon, magnetic, and spin-phonon excitations inGdSr2RuCu2O8single crystals
Physical Review B, 2001
We present a polarized Raman scattering study of GdSr 2 RuCu 2 O 8 single crystals. In this compound, the RuO 6 octahedra are rotated around the c axis that in turn gives some Raman activity of the oxygen (O Ru) vibrations at 265 cm Ϫ1 (A 1g), 411 cm Ϫ1 (B 2g) and 607 cm Ϫ1 (B 1g). These vibrations, as well as those of the apical oxygen of RuO 6 at 654 cm Ϫ1 (A 1g) and the Cu-plane oxygen at 318 cm Ϫ1 (B 2g), clearly respond to the onset of magnetic ordering at T m Ϸ140 K. In particular, the 265 cm Ϫ1 mode hardens anomalously with decreasing temperature below T m. Notably, the corresponding phonon line is absent in the Raman spectra of GdSr 2 NbCu 2 O 8 (Nb 5ϩ :4d 0), a compound isomorphic to GdSr 2 RuCu 2 O 8 (Ru 5ϩ :4d 3). We argue that the eigenvector of the 265 cm Ϫ1 phonon ͑rotational mode͒ facilitates efficient modulation of the Ru(t 1g)-O Ru (p) bands. This modulation gives both Raman scattering strength to the 265 cm Ϫ1 mode and strong spin-phonon coupling.
Evidence for strong electron-phonon coupling and polarons in the optical response of La2−xSrxCuO4
Physica C: Superconductivity, 1997
The normal state optical response of La 2−x Sr x CuO 4 is found to be consistent with a simple multi-component model, based on free carriers with strong electron-phonon interaction, localized polaronic states near 0.15 eV and a mid-infrared band at 0.5 eV. Normal state reflectance and absorbance of La 1.83 Sr 0.17 CuO 4 are investigated and their temperature dependence is explained. Both, the ac and dc response are recovered and the quasi-linear behavior of the optical scattering rate up to 3000 − 4000 cm −1 is found to be consistent with strong electron-phonon interaction, which also accounts for the value of T c . Although not strictly applicable in the superconducting state, our simple model accounts for the observed penetration depth and the optical response below T c can be recovered by introducing a small amount of additional carriers. Our findings suggest that the optical response of La 2−x Sr x CuO 4 could be explained both, in the normal and superconducting state, by a simple multi-fluid model with strong electron-phonon interaction if the gap symmetry and the temperature dependence of the 0.5 eV MIR band are adequately taken into account. 74.20.De, 74.25Fy, 74.25Gz, 74.72Dn Typeset using REVT E X
Raman and infrared (IR) spectra of an underdoped La1.90Sr0.10CuO4 single crystal have been measured as a function of temperature. Both techniques provide unconventional low-energy spectra. The IR conductivity exhibits features peaked at finite frequencies which do not have a counterpart in the Raman response. Below approximately 100 K a transfer of both Raman and IR spectral weight towards lower energies is found and a new component in the Raman response builds up being characterized by a very long lifetime of electrons propagating along the Cu-O bonds.
Raman scattering study of electronic and magnetic excitations in La2−Sr CuO4
Physica C: Superconductivity, 2003
Electronic and magnetic excitations with A 1g-symmetry have been investigated by the polarized Raman scattering in the energy region between 0 and 4000 cm À1 for La 2Àx Sr x CuO 4 (x ¼ 0, 0.1, 0.113, 0.15, 0.22). In the bða; aÞ b b polarization both magnetic and electronic excitations are allowed, while only electronic excitation for bðc; cÞ b b. In x 6 0:15, the intensity of bða; aÞ b b is larger than that of bðc; cÞ b b due to the additional existence of the magnetic excitation, however, both spectra become the same for x ¼ 0:22. This result is the experimental evidence that dynamical magnetic fluctuation disappears in the over-doped region in La 2Àx Sr x CuO 4 .
Journal of Physics: Condensed Matter, 1992
The polarized Raman spectra of Ca2Cu03, C a l. s S r~.~C u O~ and Ca1.6Sro.rCuO3 single oystals and the IR transmission spenra of Ca~Cu03 and Cal.aSro.rOuO~ have been measured. The frequencies of all I'point phonons of Ca2Cuo3 have been dclermined on the basis of assignment of the one-phonon Raman (4) and IR lines 10 definite normal modes and alculalions of the lattice dynamics. The line assignment is wnsislenl wilh earlier mults for Cal.gSr0.2ChO3 as well BS with the line shifts upon substitution of Sr for Ca. I h e inlensive bmad lines in the (bb)polarized Raman speclra of both Sr-free and Sr-subtiluted ?ample (in addition l o the two As Lines already assigned) have been attributed to resonanlly enhanced two-phonon scattering involving modes related 10 motions of Cu andlor O(2) atoms. A coincidence has k e n found between most of the line frequencies and half-widlhs in the (bb)polarized Raman spectra and some of the maxima in the two-phonon density of stales as oblained fmm lattice dynamirs calculations.