学术报告
题目: [超导国家重点实验室学术报告] SQUID and Steward-McCumber parameter
时间: 2013年11月04日 09:30
地点: D210会议室
报告人: Yi Zhang
Peter Grünberg Institute (PGI-8), Forschungszentrum Jülich (FZJ), D-52425 Jülich, Germany
报告摘要：
We investigated helium-cooled niobium thin film SQUIDs with different Steward-McCumber parameter βc. Three important SQUID parameters, the intrinsic noise dFs, the voltage-to-flux transfer coefficient ¶V/¶F and the dynamic resistance Rd, increase with increasing bc. The V - F curves of dc SQUIDs can be generally described as quasi-sine waves when bc < 1 and quasi-square waves, if bc > 1. No hysteresis was observed in the current - voltage (I - V) characteristics of the SQUIDs, even for βc » 17. We attribute the absence of hysteresis to a random switching noise, Sv, of the junctions, which increases the SQUID intrinsic noise dFs. It can be represented by an effective noise temperature T* of the SQUID which is higher than the bath temperature T, thus leading to high values of the effective thermal rounding parameter G* and further rounding of the SQUID I - V curve.
报告人简介：
Yi Zhang, Peter Grünberg Institute (PGI-8), Forschungszentrum Jülich (FZJ), D-52425 Jülich, Germany
Academic background and Professional career:
Yi Zhang was born in Shanghai, China. He received his Bachelor-Phys.degree in 1982 at the Jiao Tong-University, Shanghai, his Dipl.-Phys. degree in 1987 and his Ph.D. degree in 1990 at the Justus-Liebig University Gießen, Germany.
He joined the Forschungszentrum Juelich in 1990, dedicating his work to the fabrication and application of High Tc rf SQUIDs. In April 1993 he became awarded the title of an extraordinary professor for modern physics at the University of Peking and in November 1997, he became awarded the title of an extraordinary professor on the field of SQUID technologies at the Jiao Tong-University, Shanghai. In 2001, he spent four months as a guest scientist at the University of California, Berkeley, in Prof. John Clarke’s Group, working on the novel superconductor magnesiumdiboride and developing the first MgB2 SQUID. He became the title of an adviser professor at University Tongji in Shanghai in October 2002. He was one of the co-authors of “SQUID Handbook” edited by John Clarke and Alex. I. Braginski, WILEY-VCH Verlag GmbH & Co. KGaA (2004). Recently, he has been invited as adviser professor at Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, and guest professor at Jilin University (2011). He has more than 150 publications and about 30 pending or filed patents, and is one of the leading scientists for SQUIDs worldwide. Several of his works were cited in the Book “100 Years of Superconductivity” edited by Horst Rogalla and Peter H. Kes (2011), CRC Press, Taylor & Francis Group.
Research Area:
HTS and LTS SQUIDs fabrication and application
SQUID noise analysis
rf- and dc-SQUID readout electronics
MCG and fMCG measurements
Ultra Low field NMR/MRI
Earth’s field NMR
SQUID-TEM measurements in geo-exploration
联系人： 郑东宁 研究员/8264-9187
报告摘要：
We investigated helium-cooled niobium thin film SQUIDs with different Steward-McCumber parameter βc. Three important SQUID parameters, the intrinsic noise dFs, the voltage-to-flux transfer coefficient ¶V/¶F and the dynamic resistance Rd, increase with increasing bc. The V - F curves of dc SQUIDs can be generally described as quasi-sine waves when bc < 1 and quasi-square waves, if bc > 1. No hysteresis was observed in the current - voltage (I - V) characteristics of the SQUIDs, even for βc » 17. We attribute the absence of hysteresis to a random switching noise, Sv, of the junctions, which increases the SQUID intrinsic noise dFs. It can be represented by an effective noise temperature T* of the SQUID which is higher than the bath temperature T, thus leading to high values of the effective thermal rounding parameter G* and further rounding of the SQUID I - V curve.
报告人简介：
Yi Zhang, Peter Grünberg Institute (PGI-8), Forschungszentrum Jülich (FZJ), D-52425 Jülich, Germany
Academic background and Professional career:
Yi Zhang was born in Shanghai, China. He received his Bachelor-Phys.degree in 1982 at the Jiao Tong-University, Shanghai, his Dipl.-Phys. degree in 1987 and his Ph.D. degree in 1990 at the Justus-Liebig University Gießen, Germany.
He joined the Forschungszentrum Juelich in 1990, dedicating his work to the fabrication and application of High Tc rf SQUIDs. In April 1993 he became awarded the title of an extraordinary professor for modern physics at the University of Peking and in November 1997, he became awarded the title of an extraordinary professor on the field of SQUID technologies at the Jiao Tong-University, Shanghai. In 2001, he spent four months as a guest scientist at the University of California, Berkeley, in Prof. John Clarke’s Group, working on the novel superconductor magnesiumdiboride and developing the first MgB2 SQUID. He became the title of an adviser professor at University Tongji in Shanghai in October 2002. He was one of the co-authors of “SQUID Handbook” edited by John Clarke and Alex. I. Braginski, WILEY-VCH Verlag GmbH & Co. KGaA (2004). Recently, he has been invited as adviser professor at Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, and guest professor at Jilin University (2011). He has more than 150 publications and about 30 pending or filed patents, and is one of the leading scientists for SQUIDs worldwide. Several of his works were cited in the Book “100 Years of Superconductivity” edited by Horst Rogalla and Peter H. Kes (2011), CRC Press, Taylor & Francis Group.
Research Area:
HTS and LTS SQUIDs fabrication and application
SQUID noise analysis
rf- and dc-SQUID readout electronics
MCG and fMCG measurements
Ultra Low field NMR/MRI
Earth’s field NMR
SQUID-TEM measurements in geo-exploration
联系人： 郑东宁 研究员/8264-9187