Edge effect and significant increase of the superconducting transition onset temperature of 2D superconductors in flat and curved geometries

Since the discovery by Karl Alex Muller and Johannes Georg Bednorz (IBM Zurich) in January 1986 that an oxide of barium, lanthanum and copper might be superconducting at temperatures up to 35 K, the superconducting transition temperature has jumped to 125 K in only two years. A great tide of high Tc superconductor exploration has swept across the world. Like their counterparts in other countries, Chinese scientists also stood in the frontline of this revolution.When Prof. Zhao Zhongxian obtained Bednorz and Müller's paper in September 1986, he thought their ideas were reasonable. A team at the Institute of Physics, Academia Sinica was then organized to search for high Tc materials. In December 1986, Zhao and his colleagues successfully obtained superconducting samples of Sr0.25La4.75Cu5Ox with onset temperature Tcon 48.6 K and Ba0.5La4.5Cu5Ox with Tcon = 46.3 K (Figure 1). This occurred only a few days after the announcement of the confirmation of superconductivity by diamag-netic observation from Japan. These were the highest records for superconducting transition temperature Tcon in the world at that time. Moreover, a sign of superconductivity with Tc0 (zero resistivity) around 70 K was also observed in some La-Ba-Cu-O samples. Because these samples were unstable, however, the Tc decreased after several days storage in air. Since then Zhao and his colleagues have searched for materials with higher Tc by using various compositions and substitutions, different sintering processes, and heat treatments.

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Microcalorimeters for X-Ray Spectroscopy

International Astronomical Union Colloquium ◽

10.1017/s0252921100107365 ◽

1988 ◽

Vol 102 ◽

pp. 41

Author(s):

E. Silver ◽

C. Hailey ◽

S. Labov ◽

N. Madden ◽

D. Landis ◽

...

Keyword(s):

High Resolution ◽

High Efficiency ◽

Thermal Response ◽

Low Noise ◽

High Resolution Spectroscopy ◽

Superconducting Transition ◽

Sapphire Substrates ◽

Laboratory Plasmas ◽

Adiabatic Demagnetization ◽

Theoretical Predictions

The merits of microcalorimetry below 1°K for high resolution spectroscopy has become widely recognized on theoretical grounds. By combining the high efficiency, broadband spectral sensitivity of traditional photoelectric detectors with the high resolution capabilities characteristic of dispersive spectrometers, the microcalorimeter could potentially revolutionize spectroscopic measurements of astrophysical and laboratory plasmas. In actuality, however, the performance of prototype instruments has fallen short of theoretical predictions and practical detectors are still unavailable for use as laboratory and space-based instruments. These issues are currently being addressed by the new collaborative initiative between LLNL, LBL, U.C.I., U.C.B., and U.C.D.. Microcalorimeters of various types are being developed and tested at temperatures of 1.4, 0.3, and 0.1°K. These include monolithic devices made from NTD Germanium and composite configurations using sapphire substrates with temperature sensors fabricated from NTD Germanium, evaporative films of Germanium-Gold alloy, or material with superconducting transition edges. A new approache to low noise pulse counting electronics has been developed that allows the ultimate speed of the device to be determined solely by the detector thermal response and geometry. Our laboratory studies of the thermal and resistive properties of these and other candidate materials should enable us to characterize the pulse shape and subsequently predict the ultimate performance. We are building a compact adiabatic demagnetization refrigerator for conveniently reaching 0.1°K in the laboratory and for use in future satellite-borne missions. A description of this instrument together with results from our most recent experiments will be presented.

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Observation by HVEM of the martensite transformation and the superconducting transition in Nb3Sn

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106004 ◽

1988 ◽

Vol 46 ◽

pp. 788-789

Author(s):

M. A. Kirk ◽

M. C. Baker ◽

B. J. Kestel ◽

H. W. Weber

Keyword(s):

Thin Films ◽

Low Temperature ◽

Superconducting State ◽

Martensite Transformation ◽

Sputter Deposition ◽

Diffusion Reaction ◽

Solute Diffusion ◽

Superconducting Transition ◽

Twin Boundaries ◽

Martensite Structure

It is well known that a number of compound superconductors with the A15 structure undergo a martensite transformation when cooled to the superconducting state. Nb3Sn is one of those compounds that transforms, at least partially, from a cubic to tetragonal structure near 43 K. To our knowledge this transformation in Nb3Sn has not been studied by TEM. In fact, the only low temperature TEM study of an A15 material, V3Si, was performed by Goringe and Valdre over 20 years ago. They found the martensite structure in some foil areas at temperatures between 11 and 29 K, accompanied by faults that consisted of coherent twin boundaries on {110} planes. In pursuing our studies of irradiation defects in superconductors, we are the first to observe by TEM a similar martensite structure in Nb3Sn.Samples of Nb3Sn suitable for TEM studies have been produced by both a liquid solute diffusion reaction and by sputter deposition of thin films.

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