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講演者：Dr. Cristina Buzea (RIEC & NICHe, 東北大学)

日時： ２月１５日（金）　午後４時半から
場所： 青山学院大学　理工学部（世田谷キャンパス）　一号館　５階　１５３８号室

講演題目： MgB₂ - A Review of Normal and Superconducting Properties

要旨： We present the main normal and superconducting state properties of magnesium diboride, a material known since early 1950's, but recently discovered by Prof. Akimitsu's group to be superconductive at a remarkably high critical temperature T_c=40K. What makes MgB₂ so special? Its high T_c, simple crystal structure, large coherence lengths, high critical current densities and fields, transparency of grain boundaries to current promises that MgB₂ will be a good material for both large scale applications and electronic devices. During the last year, MgB₂ has been fabricated in various forms, bulk, single crystals, thin films, tapes and wires. The largest critical current densities >10MA/cm² and critical fields 40T are achieved for thin films. The anisotropy ratio inferred from upper critical field measurements is still to be resolved, a wide range of values being reported, g = 1.2 ~ 9. Also there is no consensus about the existence of a single anisotropic or double energy gap. One central issue is whether or not MgB₂ represents a new class of superconductors, being the tip of an iceberg who awaits to be discovered. Up to date MgB₂ holds the record of the highest T_c among simple binary compounds. However, the discovery of superconductivity in MgB₂ revived the interest in non-oxides and initiated a search for superconductivity in related materials, several compounds being already announced to become superconductive: TaB₂, BeB_2.75, C-S composites, and the elemental B under pressure.