1997 Fiscal Year Final Research Report Summary
Superconductor/Insulator transition in two dimensional amorphous W ultra-thin film
| Project/Area Number |
08640442
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | CHIBA UNIVERSITY |
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Principal Investigator |
KUWASAWA Yoshinori Faculty of Science ; CHIBA UNIVERSITY Associate Professor, 理学部, 助教授 (60009602)
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| Co-Investigator(Kenkyū-buntansha) |
NOJIMA Tsutomu Faculty of Science ; CHIBA UNIVERSITY Assistant researcher, 理学部, 助手 (80222199)
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| Project Period (FY) |
1996 – 1997
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| Keywords | Superconductivity / Superconductor-Insulator transition / Amorphous / Quantum sheet resistance / Phase fluctuation / Superconducting order parameter / Kostelize-Thoughless transition / Thin film |
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| Research Abstract |
Amorphous W thin film (a-W) keeps a superconductivity down to the thickness of 1.2nm. Then this material is useful on the research of superconductivity of two dimensional disorder systems. In this research, two kinds of samples, Si/a-W/Si and a-W/Si multilayrs, were prepared and their superconducting characteristics were investigated. The following results were produced.
1.Observation of disorder induced Superconductor-Insulator (S/I) transition in Si/a-W/Si stucture
We measured the critical temperatures for various a-W film thickness with d_W=1-10nm. In d_W*1nm, superconductivity disappears and T-dependence of sheet resistance R_<sq> follows to the exp (T^<-1/3>) 's law. In the dependence of critical temperature T_<co> upon normal R_<sq> for d_W*1.2nm, the superconductivity disappears when R_<sq> equals to the quantum sheet resistance h/4e^2. This system indicates a typical disorder induced S/I transition.
2.Kostelize-Thoughless (KT) transition in a-W/Si multilayrs
KT-transition is the second phase transition where the vortex-antivortex pairs are induced near Tc by the thermal fluctuation of phase in order parameter. Due to the detail measurements of I-V characteristics at zero field, (1) the relation of KT transition and superconducting coupling between a-W layrs was investigated by the change of thickness of Si layr and (2) the vortex loop excitation at KT-transition was observed by controlling the number of bilayrs.
3.Observation of magnetic induced S-I transition in Si/a-W/Si structure.
In the samples with W-thickness of 1.2-3nm, the field induced S-I transition was observed by the temperature dependence of sheet resistance. Whether such a transition is vortex to Bose glass one caused by the fluctuation of superconducting phase or not was studied by analyzing the data with the Fisher's scaling law.
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