Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080, USA.
Phys Rev Lett. 2015 Mar 20;114(11):110401. doi: 10.1103/PhysRevLett.114.110401. Epub 2015 Mar 17.
The experimental observation of traditional Zeeman-field induced Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids has been hindered by various challenges, in particular, the requirement of low dimensional systems. In 2D, finite temperature phase fluctuations lead to an extremely small Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for FFLO superfluids, raising serious concerns regarding their experimental observability. Recently, it was shown that FFLO superfluids can be realized using a Rashba spin-orbit coupled Fermi gas subject to Zeeman fields, which may also support topological excitations such as Majorana fermions in 2D. Here we address the finite temperature BKT transition issue in this system, which may exhibit gapped, gapless, topological, and gapless topological FF phases. We find a large BKT transition temperature due to large effective superfluid densities, making it possible to observe 2D FF superfluids at finite temperature. In addition, we show that gapless FF superfluids can be stable due to their positive superfluid densities. These findings pave the way for the experimental observation of 2D gapped and gapless FF superfluids and their associated topological excitations at finite temperature.
传统塞曼场诱导的富勒-费雷尔-拉金-奥夫钦尼科夫（FFLO）超流体的实验观测受到各种挑战的阻碍，特别是对低维系统的要求。在二维空间中，有限温度的相位涨落导致 FFLO 超流体的 Berezinskii-Kosterlitz-Thouless（BKT）转变温度极低，这对其实验可观测性提出了严重的质疑。最近，研究表明，在受到塞曼场作用的拉什巴自旋轨道耦合费米气体中可以实现 FFLO 超流体，这在二维空间中也可能支持马约拉纳费米子等拓扑激发。在本文中，我们解决了该系统中的有限温度 BKT 转变问题，该系统可能表现出带隙、无带隙、拓扑和无带隙拓扑 FF 相。我们发现，由于较大的有效超导密度，BKT 转变温度很大，这使得在有限温度下观察二维 FF 超流体成为可能。此外，我们还表明，由于其正的超导密度，无带隙 FF 超流体可以稳定存在。这些发现为在有限温度下实验观测二维带隙和无带隙 FF 超流体及其相关拓扑激发铺平了道路。
