Racah Institute of Physics, The Hebrew University of Jerusalem , Jerusalem 9190401, Israel.
Department of Electrical Engineering, Princeton University , Princeton, New Jersey 08544, United States.
Nano Lett. 2016 Jun 8;16(6):3726-31. doi: 10.1021/acs.nanolett.6b01061. Epub 2016 May 23.
The possible phases and the nanoscale particle correlations of two-dimensional interacting dipolar particles is a long-sought problem in many-body physics. Here we observe a spontaneous condensation of trapped two-dimensional dipolar excitons with internal spin degrees of freedom from an interacting gas into a high density, closely packed liquid state made mostly of dark dipoles. Another phase transition, into a bright, highly repulsive plasma, is observed at even higher excitation powers. The dark liquid state is formed below a critical temperature Tc ≈ 4.8 K, and it is manifested by a clear spontaneous spatial condensation to a smaller and denser cloud, suggesting an attractive part to the interaction which goes beyond the purely repulsive dipole-dipole forces. Contributions from quantum mechanical fluctuations are expected to be significant in this strongly correlated, long living dark liquid. This is a new example of a two-dimensional atomic-like interacting dipolar liquid, but where the coupling of light to its internal spin degrees of freedom plays a crucial role in the dynamical formation and the nature of resulting condensed dark ground state.
二维相互作用的偶极子粒子的可能相和纳米级粒子相关性是多体物理中一个长期以来备受关注的问题。在这里，我们观察到被困二维偶极激子从相互作用气体中自发凝聚成高密度、紧密堆积的液体状态，主要由暗偶极子组成。在更高的激发功率下，观察到另一个进入明亮、高排斥等离子体的相变。暗液状态在临界温度 Tc ≈ 4.8 K 以下形成，其表现为自发的空间凝聚到更小、更密集的云，表明相互作用具有吸引力部分，超出了纯粹的排斥偶极-偶极力。在这种强关联、长寿命的暗液中，量子力学涨落的贡献预计是显著的。这是二维类原子相互作用偶极液体的一个新例子，但光与其内部自旋自由度的耦合在动态形成和产生的暗基态的性质中起着关键作用。
