Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
Nature. 2011 Nov 30;480(7375):75-8. doi: 10.1038/nature10627.
Pairing of fermions is ubiquitous in nature, underlying many phenomena. Examples include superconductivity, superfluidity of (3)He, the anomalous rotation of neutron stars, and the crossover between Bose-Einstein condensation of dimers and the BCS (Bardeen, Cooper and Schrieffer) regime in strongly interacting Fermi gases. When confined to two dimensions, interacting many-body systems show even more subtle effects, many of which are not understood at a fundamental level. Most striking is the (as yet unexplained) phenomenon of high-temperature superconductivity in copper oxides, which is intimately related to the two-dimensional geometry of the crystal structure. In particular, it is not understood how the many-body pairing is established at high temperature, and whether it precedes superconductivity. Here we report the observation of a many-body pairing gap above the superfluid transition temperature in a harmonically trapped, two-dimensional atomic Fermi gas in the regime of strong coupling. Our measurements of the spectral function of the gas are performed using momentum-resolved photoemission spectroscopy, analogous to angle-resolved photoemission spectroscopy in the solid state. Our observations mark a significant step in the emulation of layered two-dimensional strongly correlated superconductors using ultracold atomic gases.
在自然界中，费米子配对无处不在，它是许多现象的基础。例如超导性、(3)He 的超流性、中子星的异常旋转，以及强相互作用费米气体中二聚体的玻色-爱因斯坦凝聚和 BCS（Bardeen、Cooper 和 Schrieffer）区之间的交叉。当限制在二维时，相互作用的多体系统会表现出更微妙的效应，其中许多效应在根本上都没有得到理解。最引人注目的是铜氧化物中高温超导（迄今仍未解释）的现象，它与晶体结构的二维几何密切相关。特别是，目前还不清楚在高温下是如何建立多体配对的，以及它是否先于超导性。在这里，我们报告了在强耦合条件下，在谐被俘获的二维原子费米气体中，观察到的在超流转变温度以上的多体配对能隙。我们使用动量分辨光发射谱测量气体的谱函数，类似于固态中的角分辨光发射谱。我们的观察标志着使用超冷原子气体模拟层状二维强关联超导材料的重要一步。
