[Icqm_seminar] 12.12seminar
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报告题目：
Triplet-spin pairing and the quest to discover a room-temperature superconductor
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报 告 人：
Richard A. Klemm
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报告时间：
2013年12月12日（周四）晚18：40
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报告地点：
理科教学楼419室
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Abstract：
This special lecture for the PKU class on Physical Properties of Quantum Materials consists of two nearly independent parts. Part 1 is on triplet superconductors, the most exotic form of unconventional superconductivity. As for triplet-spin superfluid 3He, p-wave orbital superconducting order parameter (OP) symmetries can be nodeless, as in the Balian-Werthamer state or have point nodes, as in the chiral Anderson-Brinkman-Morel (ABM) state. However, unlike 3He, the OP can also lock onto a crystal symmetry direction. The OP can have the non-chiral polar or chiral ABM and Scharnberg-Klemm state forms, that contain only one crystal lattice p-wave OP component such as pz, or a general mix of the chiral axial px±ipy states. Transitions between these states can occur at various field angles and temperatures. Experimental results on UPt3, URhGe, UCoGe, UGe2, and Sr2RuO4 will be summarized, and comparisons with theoretical calculations of the upper critical field for p-wave superconductors will be shown. Knight-shift measurements in the superconducting phases of some of these candidate materials have suggested parallel-spin states, but in Sr2RuO4, those suggestions are in direct conflict with the upper critical field measurements. Examples of conflicting upper critical field and Knight-shift measurements in other layered superconductors will be shown, along with plausible explanations for the disagreements.
Part 2 is on major portions of Layered Superconductors Volume 2 (Oxford University Press, to be published). Since non-stoichiometric Bi2Sr2CaCu2O8+d (BSCCO) is a misfit compound with incommensurate alternating metallic (or superconducting) CuO2 layers and insulating BiO layers, it behaves as a stack of intrinsic Josephson junctions (IJJs). These IJJs serve two purposes: coherent THz emission due to the ac Josephson effect, and Josephson tunneling probes of the orbital symmetry of the superconducting OP that are both insensitive to competing charge- and spin-density wave OPs and to the known exceedingly strong oxygen inhomogeneities near the crystal surfaces and/or grain boundaries. Recent experiments on BSCCO have confirmed the conclusions of earlier c-axis twist junction experiments that the superconducting OP in BSCCO is s-wave for all temperatures up to the superconducting transition temperature Tc ~80 K. Other recent results with the same conclusion for the so-called electron-doped superconductors will be shown. The s-wave orbital symmetry of the superconducting OP strongly implies an attractive pairing mechanism, providing a crucial clue for young experimenters in their quest to discover a room-temperature superconductor.
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About the speaker:
Professor Richard A. Klemm is Professor of University of Central Florida, Orlando, His main current research interests include layered superconductors, p-wave superconductors, coherent THz emission.
He obtained his first degree (1969) in Stanford University, and PhD (1974) in Harvard University, where he finished his thesis, which title was Layered Superconductors. After two year’s Postdoctoral fellow in Stanford University 1974-76, he was Employed by Iowa State and Ames Laboratory 1976-1981 (tenured 1980), and then he worked for Exxon Research and Engineering Co. 1981-1986 and Argonne National Laboratory 1990-2000. Now he is the Author of more than 170 refereed articles and one book, Layered Superconductors Volume 1 (Oxford University Press, 2012), and Fellow and Outstanding Referee of the APS.
