E. L. Ginzton Laboratory, Stanford University, Stanford, CA 94305, USA.
Proc Natl Acad Sci U S A. 2012 Apr 24;109(17):6467-72. doi: 10.1073/pnas.1107970109. Epub 2012 Apr 11.
We create a large exciton-polariton condensate and employ a Michelson interferometer setup to characterize the short- and long-distance behavior of the first order spatial correlation function. Our experimental results show distinct features of both the two-dimensional and nonequilibrium characters of the condensate. We find that the gaussian short-distance decay is followed by a power-law decay at longer distances, as expected for a two-dimensional condensate. The exponent of the power law is measured in the range 0.9-1.2, larger than is possible in equilibrium. We compare the experimental results to a theoretical model to understand the features required to observe a power law and to clarify the influence of external noise on spatial coherence in nonequilibrium phase transitions. Our results indicate that Berezinskii-Kosterlitz-Thouless-like phase order survives in open-dissipative systems.
我们制备了一个大的激子极化激元凝聚体，并采用迈克尔逊干涉仪来对一级空间关联函数的短程和长程行为进行了表征。我们的实验结果显示出凝聚体的二维和非平衡特征的明显特征。我们发现，正如二维凝聚体所预期的那样，在短距离处的高斯衰减之后，在更长的距离处出现了幂律衰减。幂律的指数在 0.9-1.2 的范围内，大于在平衡态下可能的数值。我们将实验结果与理论模型进行了比较，以理解观察到幂律所需的特征，并澄清外部噪声对非平衡相变中空间相干性的影响。我们的结果表明，类似于 Berezinskii-Kosterlitz-Thouless 的相序在开放耗散系统中得以幸存。
