#################################################### # T. Egami # requesting 7 days, at minimum= days # beamline 33ID, "Electronic inhomogeneity in the superconducting cuprates probed by" #################################################### # top:/home/www/beamtime-requests/req00349.txt # UNICAT Member Beam Time Request #349 # created Mon Dec 23 10:43:48 CST 2002 #################################################### beamline: 33ID collaboration: No contact: egami@seas.upenn.edu days: 7 description: UNICAT Proposal (Nov. 12, 2002) Title: Electronic inhomogeneity in the superconducting cuprates probed by anomalous x-ray scattering PI: T. Egami Collaborators: Jae-Ho Chung graduate student Eugene Mamontov postdoctoral fellow Przemek Piekarz postdoctoral fellow Wojtek Dmowski research associate Beam line: 33-ID Requested beam time: 7 days at a time, 14 days in total. Abstract: Diffuse scattering from local distortions and phonons in detwinned single crystals of superconducting YBa2Cu3O6.95 will be measured with the incident energy in the vicin-ity of the Cu-Ka edge, to determine the electronic inhomogeneity in the sample. When q = Q ? K is small f?(E, q) should reflect the average electronic state, while when q is suffi-ciently large, it should show the two-phase behavior corresponding to the electronic in-homogeneity, such as the one observed by scanning tunneling spectroscopy. Background It is already 16 years since the high-temperature superconductivity (HTSC) was discovered, but its mechanism still remains a mystery. Part of the reason is that the con-ventional theories all assume that the electronic state is spatially homogeneous, since in-homogeneity is generally harmful to superconductivity. However, there are a large num-ber of experimental data that show that the HTSC cuprates are not spatially homogene-ous. For instance the local lattice distortion is always found [1], and the recent scanning tunneling spectroscopy (STS) clearly shows the electronic inhomogeneity [2,3]. How-ever, the STS study suffers from the effect of the surface, so that critics suspect that the bulk is still homogeneous. In order to show directly the charge inhomogeneity of the bulk we propose the measurement of anomalous dispersion, f?(E, q), as a function of q in the vicinity of the Cu Ka edge. It is known that the doped holes induce changes in the x-ray absorption spectrum near the edge. This will produce corresponding changes in the real part of the anomalous dispersion, f?(E, q), which can be determined through the measurement of diffuse scattering as a function of incident energy. Our recent study with a single crystal of KNbO3 established a technique of determining f?(E, q) through the measurement of absorption spectra and diffuse scattering [4]. Measurement Diffuse scattering from local distortions and phonons in detwinned single crystals of superconducting YBa2Cu3O6.95 will be measured with the incident energy in the vicin-ity of the Cu-Ka edge. Samples measure 1 x 1.5 x 5 mm3, and are detwinned by thermal treatment under stress. We will first measure the absorption spectrum by monitoring the fluorescence yield. The XANES will establish the energy range where anomalies are ex-pected. By scanning through energy at various values of q = Q ? K, f?(E, q) can be de-termined as a function of E and q. It is expected that at the long wave limit f? reflects the average electronic structure, while at the short waves it shows the two-phase behavior if electronic inhomogeneity is present. The crossover value of q tell us the spatial extention of electronic inhomogeneity. Since the intensity of diffuse scattering is low, and we have to separate it from the background, long measurement times are required. We expect to measure scattering at at least 20-30 different values of q and map out the inhomogeneity in q-space. Thus 7 days are required for one set of measurement. We hope to measure diffuse scattering around at least 3 Bragg peaks with different nature (inter-planar correlation, longitudinal vs. transverse). Impact The issue of electronic inhomogeneity is one of the hottest foci in the study of HTSC cuprates. A very strong impact is expected if we can prove the presence of bulk electronic inhomogeneity and its dimension. References: 1. T. Egami and S. J. L. Billinge, in Physical Properties of High Temperature Su-perconductors V, ed. D. M. Ginsberg (World Scientific, Singapore, 1996) p. 265. 2. K. M. Lang, V. Madhavan, J. E. Hoffman, E. W. Hudson, H. Eisaki, S. Uchida and J. C. Davis, Nature 415, 412 (2002). 3. S. H. Pan, J. P. O'Neal, R. L. Badzey, C. Chamon, H. Ding, J. R. Engelbrecht, Z. Wang, H. Eisaki, S. Uchida, A. K. Guptak, K. W. Ng, E. W. Hudson, K. M. Lang and J. C. Davis, Nature 413, 282 (2001). 4. E. Mamontov, T. Egami, W. Dmowski, T. Gog, and C. Venkataraman, Phys. Rev. B, in press. equipment+required: experiment: Electronic inhomogeneity in the superconducting cuprates probed by foreign+nationals: ??????? hazards: minimumdays: name: T. Egami new+request: on nonmembers: Jae-Ho Chung graduate student Eugene Mamontov postdoctoral fellow Przemek Piekarz postdoctoral fellow Wojtek Dmowski research associate unacceptable+dates: #REMOTE_HOST: pwk.uni.aps.anl.gov #REMOTE_ADDR: 164.54.216.37 #CONTENT_LENGTH: 5388 #HTTP_REFERER: http://www.uni.aps.anl.gov/unireq.htm #HTTP_USER_AGENT: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:0.9.2) Gecko/20010726 Netscape6/6.1