X-ray diffuse scattering studies of the local structural inhomogeneities in high temperature superco...

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" X-ray diffuse scattering studies of the local structural inhomogeneities in high temperature superconductors "
Xuerong Liu S. K. Sinha

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	52431
Doc. No	:	TL22385
Call number	:	‭3339219‬
Main Entry	:	Xuerong Liu
Title & Author	:	X-ray diffuse scattering studies of the local structural inhomogeneities in high temperature superconductors\ Xuerong Liu
College	:	University of California, San Diego
Date	:	2009
Degree	:	Ph.D.
student score	:	2009
Page No	:	148
Abstract	:	The high temperature superconductivity in cuprates is realized by off-stoichiometric doping. In addition to contributing carriers to the CuO2 planes, the dopants inherently introduce local disorder into the systems. Using the X-ray diffuse scattering technique, we studied the dopant-induced local structural distortions in two cuprate compounds: La1.92 Sr0.08 CuO 4 and YBa2 Cu3 O6.92 . On La1.92 Sr0.08 CuO4 , strong anisotropic diffuse scattering pattern on top of the diffuse scattering due to thermal vibrations was observed. Our quantitative analysis shows that the observed anisotropic X-ray diffuse scattering intensities can be well described by the Huang Diffuse Scattering(HDS) theory with the single defect approximation, which indicates the Sr dopants are randomly distributed in the crystal. Based on the fitted parameters, the Sr-dopant induced elastic lattice distortion pattern was reconstructed. The big amplitude of the elastic lattice distortion near the Sr dopants suggests that Sr-dopant induced local structural modulation might be the origin of the electronic inhomogeneities observed with scanning tunneling microscopy experiments. The oxygen vacancies in YBa2 Cu3 O6.92 behave in a different way. Our X-ray diffuse scattering measurements reveal that majority of the oxygen vacancies tend to cluster together and are ordered to form a 4-unit-cell superstructure with [Special characters omitted.] <math> <f> <a><ac>q<inf>0</inf></ac><ac></ac></a>=<fr><nu>1</nu> <de>4</de></fr>,0,0</f> </math> along a* direction. The superlattice consists of large anisotropic displacements of Cu, Ba, and O atoms, respectively and appears to be consistent with the presence of an O-ordered "Ortho-IV" phase. These "Ortho-IV" minority phase islands also induce long-range strains to the surrounding lattices, which manifest themselves as HDS observed in our experiments. Our quantitative analysis further revealed a b direction lattice modulation within the islands with the wavevector to be [Special characters omitted.] <math> <f> <a><ac>q<inf>1</inf></ac><ac></ac></a></f> </math> = (0; 0:21; 0). The fact that [Special characters omitted.] <math> <f> <a><ac>q<inf>1</inf></ac><ac></ac></a></f> </math> is very close to the nesting vector connecting the nearly nested Fermi surface(FS) "ridges" originated from the metallic Cu-O chains strongly indicates that the b direction modulation is induced by the FS effect.
Subject	:	Pure sciences; Cuprates; Diffuse scattering; Inhomogeneity; Structure; X-ray; Structural inhomogeneities; Condensed matter physics; 0611:Condensed matter physics
Added Entry	:	S. K. Sinha
Added Entry	:	University of California, San Diego