Center for Subwavelength Optics and Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea.
Phys Rev Lett. 2013 Apr 26;110(17):175302. doi: 10.1103/PhysRevLett.110.175302. Epub 2013 Apr 25.
We measure the in-plane distribution of thermally activated vortices in a trapped quasi-2D Bose gas, where we enhance the visibility of density-depleted vortex cores by radially compressing the sample before releasing the trap. The pairing of vortices is revealed by the two-vortex spatial correlation function obtained from the vortex distribution. The vortex density decreases gradually as temperature is lowered, and below a certain temperature, a vortex-free region emerges in the center of the sample. This shows the crossover from a Berezinskii-Kosterlitz-Thouless phase containing vortex-pair excitations to a vortex-free Bose-Einstein condensate in a finite-size 2D system.
我们测量了被俘获的准二维玻色气体中热激活涡旋的面内分布，通过在释放陷阱之前对样品进行径向压缩，增强了密度耗尽的涡旋核的可见度。通过从涡旋分布中获得的双涡旋空间相关函数揭示了涡旋的配对。随着温度的降低，涡旋密度逐渐降低，并且在一定温度以下，样品中心出现无涡旋区域。这表明从包含涡旋对激发的 Berezinskii-Kosterlitz-Thouless 相到有限尺寸 2D 系统中的无涡旋玻色-爱因斯坦凝聚体的转变。
