Stability of supercurrents in a superfluid phase of spin-1 bosons in an optical lattice
Stability of supercurrents in a superfluid phase of spin-1 bosons in an optical lattice
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DOI：
10.1103/physreva.103.043305
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发表时间：
2020-12
期刊：
影响因子：
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通讯作者：
Shion Yamashika;R. Yoshii;S. Tsuchiya
中科院分区：
文献类型：
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作者：
Shion Yamashika;R. Yoshii;S. Tsuchiya
基于由自旋-1玻色-哈伯德模型导出的时间相关金兹堡-朗道（TDGL）方程，研究了光学晶格中具有反铁磁相互作用的自旋-1玻色子的集体模式和超流动性。具体地说，我们考察了在莫特绝缘相附近的极性相中，具有均匀填充因子的超电流的稳定性。通过求解线性化的TDGL方程，我们得到了由于自旋空间中$S^2$对称性的破坏而产生的极性相的无间隙自旋向列模式和有间隙自旋波模式。超流表现出由增长的集体模态引起的动力不稳定性。与二阶相变相比，一阶超流体-莫特绝缘子相变的临界动量在相边界处是有限的。此外，临界动量在整个亚稳SF相中保持有限，并在相边界处趋近于零，此时亚稳SF态消失。我们还研究了自旋电流的稳定性，这是由最近的自旋气体实验引起的。发现自旋电流的临界动量为零，其中自旋向列模式导致动力不稳定。我们研究了自旋电流零临界动量的起源，发现它归因于即使在无限小的自旋电流存在的情况下，极性状态也变得能量不稳定。讨论了自旋电流零临界动量对极态稳定性的影响。
We study collective modes and superfluidity of spin-1 bosons with antiferromagnetic interactions in an optical lattice based on the time-dependent Ginzburg-Landau (TDGL) equation derived from the spin-1 Bose-Hubbard model. Specifically, we examine the stability of supercurrents in the polar phase in the vicinity of the Mott insulating phase with even filling factors. Solving the linearized TDGL equation, we obtain gapless spin-nematic modes and gapful spin-wave modes in the polar phase that arise due to the breaking of $S^2$ symmetry in spin-space. Supercurrents exhibit dynamical instabilities induced by growing collective modes. In contrast to the second-order phase transition, the critical momentum of mass currents is finite at the phase boundary of the first-order superfluid-Mott insulator (SF-MI) phase transition. Furthermore, the critical momentum remains finite throughout the metastable SF phase and approaches zero towards the phase boundary, at which the metastable SF state disappears. We also study the stability of spin currents motivated by recent experiments for spinor gases. The critical momentum of spin currents is found to be zero, where a spin-nematic mode causes the dynamical instability. We investigate the origin of the zero critical momentum of spin currents and find it attributed to the fact that the polar state becomes energetically unstable even in the presence of an infinitesimal spin current. We discuss implications of the zero critical momentum of spin currents for the stability of the polar state.