Study on the formation mechanism of long-distance proximity effect

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 07650017
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Applied materials science/Crystal engineering
• Research Institution: Himeji Institute of Techology
• Principal Investigator: KISHINO Seigo Himeji Institute of Technology, Faculty of Engineering, Professor, 工学部, 教授 (50201455)
• Co-Investigator(Kenkyū-buntansha): MATSUDA Tetsuro Himeji Institute of Technology, Faculty of Engineering, Associated professor, 工学部, 助教授 (10047582) ; YOSHIDA Haruhiko Himeji Institute of Technology, Faculty of Engineering, Assistant Professor, 工学部, 助手 (90264837)
• Project Period (FY): 1995 – 1996
• Keywords: oxide high temperature superconductor / proximity effect / variable hopping conduction / localized state

Research Abstract

Electrical conduction of LCMO (La_<0.7>Ca_<0.3>MnO_2) film has been studied in order to make clear the formation mechnaism of long-distance proximity effect. The long-distance proximity effect has been reported in the S-I-S junction using a combination of YBCO (YBa_2 Cu_3 O_<7-X>) and LCMO in which the LCMO film is used as a sandwiched insulator. For this purpose it is essential to study the electrical properties of LCMO in the low temperature region below l00k.
In this study the transient current of the DCTS (Discharging Current Transient Spectroscopy) was measured besides the measurement of conventional resistivity versus temperature property. Normally, DCTS is a method used for the measurement of localized states in insulators. However, we have found in this study that the property of the transient current varies according to the temperature of the LCMO below 200 K.Namely, the change in the property of the current versus time curve occurred at the temperature when metallic LCMO turned to variable hopping LCMO and variable hopping to insulating LCMO,respectively. This shows that phase transition occurred at the temperature in which the property of the current versus time curve changed. The transition temperature was nearly in agreement with the temperature that the property of the conventional resistivity versus temperature curve changed.
From the observed results it is ascertained that the LCMO film does not show variable hopping conduction below 35 K when the film is formed by the sputtering technique. This might reject the possibility that the variable hopping occurs at the S-I-S junction at temperatures around 4.2 K in which "superconducting current" has been observed. However, the possibility could not be perfectly denied because the property of LCMO film depends on the growth condition of the film.