Study of vortex state in magnesium diboride superconductors -A vortex matter phase diagram originating from two superconducting gap

本文研究了典型的双能隙超导体MgB_2中的涡旋物质相图及杂质对其的影响，不仅阐明了在高温超导体中观察到的涡旋相变的普遍特征，而且发现了一种新的涡旋相变类型和Al替代对相图的调制，这被认为是该系统所特有的。我们还成功地测量了MgB_2的相关材料Ba（Fe_（0.93）Co_（0.07））_2As_2的两种带隙能。

We studied the vortex matter phase diagram in MgB2, which has been known as a typical two-gap superconductor, and the impurity effect on it. In addition to clarifying the universal characteristics of vortex phase transitions, which have been remarkably observed in high-Tc cuprate superconductors, we found a new type of transition in the vortex state and a modulation of the phase diagram due to Al substitution, which were considered to be peculiar to this system. We also succeeded in measuring the two kinds of gap energies in Ba(Fe0.93Co0.07)2As2, which is related materials of MgB2.