EPR INVESTIGATION OF La0.7Ca0.3MnO3: EVIDENCE OF SPIN-GLASS FORMATION

EPR investigations on La 0.7 Ca 0.3 MnO 3 were carried out in the temperature range from 14 K to 300 K. The important observations are: (i) a coincidence of resistivity maxima with the disappearance of paramagnetic EPR line I, which suggests that there exists a strong electron–phonon interaction, (ii) the appearance of an "out of phase" line near the Curie temperature T c due to the formation of spin clusters consisting of Mn3+ and Mn4+ ions, and (iii) the appearance of an intense EPR line III and the splitting of FC and ZFC magnetization curves below 160 K, ascribed to local magnetic frustrations. The above EPR observations provide experimental evidence for the co existence of spin fluctuations and magnetic disorders in this sample, which leads to the formation of spin-glass features below T c .

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Bosonic Spectral Function and the Electron-Phonon Interaction in HTSC Cuprates

Advances in Condensed Matter Physics ◽

10.1155/2010/423725 ◽

2010 ◽

Vol 2010 ◽

pp. 1-64 ◽

Cited By ~ 26

Author(s):

E. G. Maksimov ◽

M. L. Kulić ◽

O. V. Dolgov

Keyword(s):

Spectral Function ◽

Spin Fluctuations ◽

Strongly Correlated ◽

Phonon Interaction ◽

Strong Electron ◽

Optimal Doping ◽

Electron Phonon Interaction ◽

Wave Pairing ◽

Range Part ◽

D Wave

In this paper we discuss experimental evidence related to the structure and origin of the bosonic spectral function in high-temperature superconducting (HTSC) cuprates at and near optimal doping. Global properties of , such as number and positions of peaks, are extracted by combining optics, neutron scattering, ARPES and tunnelling measurements. These methods give evidence for strong electron-phonon interaction (EPI) with in cuprates near optimal doping. We clarify how these results are in favor of the modified Migdal-Eliashberg (ME) theory for HTSC cuprates near optimal doping. In Section 2 we discuss theoretical ingredients—such as strong EPI, strong correlations—which are necessary to explain the mechanism of d-wave pairing in optimally doped cuprates. These comprise the ME theory for EPI in strongly correlated systems which give rise to the forward scattering peak. The latter is supported by the long-range part of EPI due to the weakly screened Madelung interaction in the ionic-metallic structure of layered HTSC cuprates. In this approach EPI is responsible for the strength of pairing while the residual Coulomb interaction and spin fluctuations trigger the d-wave pairing.

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Optical Spectroscopic Studies of a Soluble Fluorene-Based Conjugated Polymer: A Hydrostatic Pressure and Temperature Study

MRS Proceedings ◽

10.1557/proc-708-bb10.7 ◽

2001 ◽

Vol 708 ◽

Author(s):

S. Guha ◽

J.D. Rice ◽

C. M. Martin ◽

W. Graupner ◽

M. Chandrasekhar ◽

...

Keyword(s):

Hydrostatic Pressure ◽

Conjugated Polymer ◽

Spectroscopic Properties ◽

Spectroscopic Studies ◽

Phonon Interaction ◽

Optical Studies ◽

Strong Electron ◽

Conjugated Molecules ◽

Electron Phonon Interaction ◽

Backbone Conformation

ABSTRACTSpectroscopic properties of conjugated molecules/polymers have varying degrees of sensitivity to backbone conformation. Optical studies are presented as a function of temperature and hydrostatic pressure, using photoluminescence and Raman scattering from two polymers with distinct differences in their backbone conformation, namely, polyfluorene (PF) and ladder type poly(para-phenylene)(m-LPPP). In contrast to the photoluminescence (PL) vibronics in mLPPP, the 0-0 PL vibronic peak in PF shows a red-shift with increasing temperatures. Pressure studies reveal that the PL spectrum of PF red-shifts and broadens with increasing pressures. The phonon lines in PF show an antiresonance effect at higher pressures indicating a strong electron-phonon interaction.

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