Institute of Physics, Chinese Academy of Sciences, Beijing, China.
Phys Rev Lett. 2011 Aug 5;107(6):065301. doi: 10.1103/PhysRevLett.107.065301. Epub 2011 Aug 1.
Mean-field Bloch bands of a Bose-Einstein condensate in a honeycomb optical lattice are computed. We find that the topological structure of the Bloch bands at the Dirac point is changed completely by atomic interaction of arbitrary small strength: the Dirac point is extended into a closed curve and an intersecting tube structure arises around the original Dirac point. These tubed Bloch bands are caused by the superfluidity of the system. Furthermore, they imply the inadequacy of the tight-binding model to describe an interacting Boson system around the Dirac point and the breakdown of adiabaticity by interaction of arbitrary small strength.
我们计算了玻色-爱因斯坦凝聚体在蜂窝状光晶格中的平均场 Bloch 能带。我们发现，原子相互作用的任意小强度完全改变了 Bloch 能带在狄拉克点的拓扑结构：狄拉克点扩展成一个封闭曲线，在原始狄拉克点周围出现一个相交的管状结构。这些管状 Bloch 能带是由系统的超流性引起的。此外，它们表明紧束缚模型在描述狄拉克点附近相互作用玻色子系统时的不适用性，以及任意小强度的相互作用导致绝热性的破坏。
