Theoretical Study of Phase Transition in Superconducting Vortex States

在2000年的第一年，我研究了两个关于三维层状超导体涡旋态的课题。首先，我给出了由平行于层的外加场诱导的约瑟夫森涡向玻璃相过渡的理论。近年来，国内外的一些实验工作证明了这一理论的正确性。其次，提出了垂直于层的场中涡旋相图的材料依赖理论，并与超导YBaCuOs的实验结果一致，认为存在一阶过渡线的较低临界点。在2001年和2002年，我们的主要兴趣转移到涡旋态的量子超导涨落效应上。首先，我和我的一个学生（H.Ishida）建立了一个微观理论，适用于非晶超导薄膜中由磁场引起的超导-绝缘体跃迁行为，并定性地解释了相应的电阻现象。此外，将这一理论从现象学上推广到微观机制仍有争议的超导铜酸盐和有机物，并证明了这些具有极低凝聚能的材料在有限温度下的强量子涨落效应引起了涡旋液体状态下的异常输运现象。

In the first year, 2000, I have studied two subjects on the vortex states in three-dimensional layered superconductors. First, I have given n theory on a transition to a glass phase of Josephson vortices induced by an applied field parallel to the layers. Recently, this theory has been justified by a couple of domestic sad foreign experimental works. Next, a theory explaining a material dependence of vortex phase diagram in fields perpendicular to the layers was proposed, and, consistently with experimental results on superconducting YBaCuOs, the presence of a lower critical point of the first order transition line was argued.In 2001 and 2002, our main interests have moved onto quantum superconducting fluctuation effects in vortex states. First, one of my students (H.Ishida) and I have formulated a microscopic theory applicable to the superconductor-insulator transition behavior induced by a magnetic field in amorphous superconducting films with s-wave pairing and have qualitatively explained the corresponding resistive phenomena. Further, this theory was phenomenologically extended to superconducting cuprates and organics of which the microscopic mechanisms are still controversial, and anomalous transport phenomena in the vortex liquid regime of these materials with very low condensation energy were shown to arise from the strong quantum fluctuation effect at finite temperatures.