Blaauwgeers R, Eltsov VB, Krusius M, Ruohio JJ, Schanen R, Volovik GE
Low Temperature Laboratory, Helsinki University of Technology, Finland.
Nature. 2000 Mar 30;404(6777):471-3. doi: 10.1038/35006583.
Linear defects are generic in continuous media. In quantum systems they appear as topological line defects which are associated with a circulating persistent current. In relativistic quantum field theories they are known as cosmic strings, in superconductors as quantized flux lines, and in superfluids and low-density Bose-Einstein condensates as quantized vortex lines. A conventional quantized vortex line consists of a central core around which the phase of the order parameter winds by 27(pi)n, while within the core the order parameter vanishes or is depleted from the bulk value. Usually vortices are singly quantized (that is, have n = 1). But it has been theoretically predicted that, in superfluid 3He-A, vortex lines are possible that have n = 2 and continuous structure, so that the orientation of the multicomponent order parameter changes smoothly throughout the vortex while the amplitude remains constant. Here we report direct proof, based on high-resolution nuclear magnetic resonance measurements, that the most common vortex line in 3He-A has n = 2. One vortex line after another is observed to form in a regular periodic process, similar to a phase-slip in the Josephson effect.
线性缺陷在连续介质中很常见。在量子系统中，它们表现为拓扑线缺陷，与循环持续电流相关。在相对论量子场论中，它们被称为宇宙弦；在超导体中，被称为量子化磁通线；在超流体和低密度玻色 - 爱因斯坦凝聚体中，被称为量子化涡旋线。传统的量子化涡旋线由一个中心核组成，序参量的相位围绕该中心核缠绕2πn，而在核心内序参量消失或从体值耗尽。通常涡旋是单量子化的（即n = 1）。但理论预测，在超流3He - A中，可能存在n = 2且具有连续结构的涡旋线，这样多分量序参量的取向在整个涡旋中平滑变化，而幅度保持恒定。在此我们基于高分辨率核磁共振测量报告直接证据，表明3He - A中最常见的涡旋线n = 2。观察到一条又一条涡旋线以规则的周期性过程形成，类似于约瑟夫森效应中的相位滑移。
