1997 Fiscal Year Final Research Report Summary
Study on Submilimeterwave Spectroscopy of Superconducting quasi-one-dimensional Quantum Wires
| Project/Area Number |
08455044
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied physics, general
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| Research Institution | Nagaoka University of Technology |
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Principal Investigator |
HAMASAKI Katuyosi Nagaoka University of Technology, Department of Electrical Engineering (Professor), 工学部, 教授 (40143820)
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| Co-Investigator(Kenkyū-buntansha) |
王 鎮 郵政省, 通信総合研究所, 室長
WANG Zeng Nagaoka University of Technology, KARC,Communication Resarch Laboratory, M.P.T.
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| Project Period (FY) |
1996 – 1997
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| Keywords | Superconductor-constrictions-Superconductor (S-c-S) device / Quasi-one-dimensional quntum wire / Andreev reflection / microwave-induced steps / 電磁波誘起ステップ / サブミリ波帯デバイス |
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| Research Abstract |
We repotr the experimental results concerning the nature of transport noise, and rf-properties in Superconductor-constrictions-Superconductor (S-c-S) quasi-one-dimensional mesoscopic device. These devices were fabricated by applying voltage pulses to an insulating Nb/Insulator/Nb (or NbN) sandwich in liquid helium (4.2K). By this method, we could continuously vary the quasiparticle current-voltage (I-V) curve from insulator to tunnel-contact and finally up to perfectly metallic conducting interface. We found that I,dV/dI vs. V characteristics is colsely with the predicrions of the Blonder, Tinkham and Klapwijk (BTK), and Octabio and BTK (OTBK) theories. We also found that noise voltage power spectral density Sv (f) decreases quickly with increasing device quality factor Q^<-1> and saturates for Q^<-1>>2. This saturation suggests that within the framework of the theoretical model (Hooge model) the defect related number of carriers near the constrictions no longer changes for Q^<-1>>2 regime. In our samples, clear and periodie dV/dI peaks were observed only for clean metallic devices. The origin of these periodic dV/dI peaks above gap voltage may be associated to the quantum size effect, or the geometrical resonance model which takes into account the quantization of the density of states in the constriction. New microwave-induced steps were observed in the current-voltage characteristics of the devices with microwave irradiation. The observed steps are different from the features of the well-known "Shapiro steps". Overall features of such microwave-induced steps can not be explained using existing models. Although the origin of these peaks is not clear yet, one possible origin of this phenomena is the interaction of microwave field with Andreev-reflected electron/hole in the constriction.
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