National High Magnetic Field Laboratory

报告人简介：

Dr. Tozer received his PhD from Johns Hopkins University in 1986 with high pressure electrical transport experiments that sought a Mott insulator transition in the molecular conductor, HMTSF-TCNQ, and joined IBM TJ Watson Research in Yorktown Heights that same year where he carried out high pressure optical studies of various semiconductors and performed the first ambient pressure anisotropic resistivity studies of the newly discovered cuprate, YBCO. He moved to DuPont Experimental Station in 1989 to carry out high pressure studies of YBCO. In 1993, Prof. Jack Crow (Director) invited him to the first user committee of the new National High Magnetic Field Laboratory in Tallahassee, FL and the next month Dr. Tozer moved to the magnet lab where he has studied unconventional superconductivity since that time-experimentally validating the theoretically proposed FFLO state in the reduced dimensional system CeCoIn5, studying the competing CDW and superconducting states in uranium via low pressure x-ray studies, utilizing pressures of 25 GPa to determine that the Fermi surface in YBCO does not reconstruct beyond the superconducting dome as had been proposed, and using Mbar pressures to synthesize and study a La-based superhydride superconductor.

报告摘要：

Four decades after Neil Ashcroft proposed in 1968 that metallic hydrogen might be a room temperature superconductor at sufficiently high density, he devised an alternate means to realize a supervalent system consisting of a hydrogen cage surrounding a host metal atom, so-called superhydrides. Rapid advances in this field have been enabled by simulations based on BCS theory. High-Tc hydrides superconductors, H3S and LaH10 series have been discovered in experiments. We synthesized a higher order La-based superhydride with superconducting temperature of 294 K that, when subjected to thermal cycling (heating and cooling to increasingly higher temperatures), morphed into a higher order system with a Tc of 556 K. Our serendipitous discovery and the less-than-ideal growth necessitate that we first understand the mechanism that allowed it to form and explore phase space that permits its growth. A multi-probe approach is being implemented to address growth-to-growth variations and follow the transformation of the initial 294 K laser heated material to higher order superconductor. This provide an understanding of this new class of superconductor that begs the question as to the upper limit of superconductivity in superhydrides and whether BCS theory can describe them.

邀请人：程金光(jgcheng@iphy.ac.cn)

联系人：胡颖（8264 9361）

报告地点：中国科学院物理研究所M楼236会议室