Spatial Distribution Analyses of Superconducting Transition Temperature in Epitaxial YBa 2 Cu 3 O 7 Film Using Variable
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Spatial Distribution Analyses of Superconducting Transition Temperature in Epitaxial YBa2Cu3O7 Film Using Variable Temperature Scanning Laser Microscopy S. Seo and C. Kwon Department of Physics and Astronomy, California State University-Long Beach, Long Beach, CA 90840, U.S.A. B.H. Park and Q.X. Jia Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, NM 87545, USA ABSTRACT The spatial distribution of superconducting properties using variable temperature scanning laser microscope (VTSLM) has been investigated. The superconducting thin film used in this study is an epitaxial YBa2Cu3O7 film photolithographically patterned to a 300 µm-wide bridge. Since the voltage response, δV(x,y) is proportional to dR/dT(x,y), the spatial distribution of superconducting transition can be obtained in VTSLM images. In the resistive transition region, there is a strong correlation between the VTSLM images and the resistance of the sample. With decreasing resistance, the area with large δV(x,y) shifts toward the ends of the bridge. This indicates that the resistive transition is not uniform and both ends of the bridge have lower transition temperature, Tc. Different currents or different output power of lasers do not affect the images. VTSLM technique is a powerful tool to image the local superconducting properties and to identify the weaker superconducting areas. INTRODUCTION Since the discovery to superconductivity in cuprate oxides, a tremendous amount of research has been devoted at fabricating new higher Tc materials, understanding the fundamental properties of these materials, and developing various power and device applications. The complicated crystal structure of high Tc superconductors (HTS) leads to their substantial spatial inhomogeneity, which is especially important because of the very short coherence length in those materials. Consequently, spatially resolved studies of HTS are very effective both to evaluate the general quality of the samples and to determine local values of important parameters. In conventional transport measurements of superconducting samples, the measured quantities such as critical current densities and critical temperatures are averaged over the whole sample and do not reflect the local distribution of the quantities. Thus, spatially resolved studies of HTS are needed to determine local values of important parameters of the samples. Recently, MO imaging technique has been successfully employed to study the flux penetration on coated conductors [1,2]. Another technique is Hall-probe magnetometry using Hall probe arrays to map the local magnetic field distribution [3]. Scanning tunneling microscopy and spectroscopy were also employed to study the spatial variation of superconductivity with nanometer resolution [4]. More direct measurement techniques to study local variations of superconducting properties in HTS are the hot-spot scanning method such as low temperature scanning electron microscopy (LTSEM) and low temperature scanning laser microscopy (LTSLM). In LTSEM experim
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