Ordering and Frustration of Flux Quantum Arrangement in Superconducting Networks

1995 Fiscal Year Final Research Report Summary

• Project/Area Number: 06452051
• Research Category: Grant-in-Aid for General Scientific Research (B)
• Allocation Type: Single-year Grants
• Research Field: 固体物性Ⅱ(磁性・金属・低温)
• Research Institution: University of Tokyo
• Principal Investigator: OSADA Toshihito Univ.of Tokyo, RCAST,Lecturer, 先端科学技術研究センター, 講師 (00192526)
• Co-Investigator(Kenkyū-buntansha): NAGAMUNE Yasushi Electrotechnical Laboratory, Reseacher, 電子技術総合研究所, 研究員
• Project Period (FY): 1994 – 1995
• Keywords: Superconducting Network / Flux Quantum / Frustration / Superconducting Critical Field

Research Abstract

The purpose of the present project is to clarify the frustrating superconducting states in superconducting thin wire nets (superconducting networks) under magnetic fields by studying the arrangement of magnetic flux quanta in superconducting loops of the system. In this work, using the two-dimensional superconducting network samples made of thin wire Al, we investigated the stability of the superconducting state under magnetic fields by measuring the very small change of the superconducting transition temperature. First, we established the fabrication process to make the network samples using the electron beam lithography technipue. Then, we constructed two types of experimental sytems to detect the small change of the superconducting transition temperature. The first one was the system to detect small resistance change at a constant temperature, but its sensitivity was not enough. The second one was the system which exactly maintains the sample temperature at the middle point of the superconducting transition and directly measures the small temperature change as a function of magnetic fields. In this case, the sample was used as a very sensitive thermometer, so that we could obtain the sufficient sensitivity. Using this system, we studied the "triangular" and "rhombic" lattice networks, and successfully observed the fine structures superposing on the flux quantization oscillations. These features reflect the stability of frustrating flux quantum arrangement. We estimated the coherence length as sub-microns from the comparison with the theoretical calculation. We also fabricated the network samples with small Hall probe array to detect the flux arrangement directly, but the systematic experiments have not completed yet.