孔洞石墨烯纳米带的电子输运性质

基于密度泛函理论的计算模拟, 对含有孔洞的zigzag型石墨烯纳米带(N=17, N为碳链数目)结构进行优化, 进一步计算得到体系存在不同孔洞时的电子输运性质. 研究结果表明: 当存在单个孔洞时, 体系的导电性不仅与量子限域效应有关, 还受到孔洞对称性的束缚, 且斜向对称比纵向对称受到的束缚更大; 对于双孔洞的情况, 由于孔洞间的耦合作用, 体系的导电性在较大距离范围内大体上随孔洞间距的增大而增强, 同时会出现一些量子现象, 这可用一维对称双势垒模型来解释.     

Observation of the BEC-BCS crossover in a degenerate Fermi gas of lithium atoms

We observe characteristic atomic behaviors in the Bose-Einstein-condensation-Bardeen-Cooper-Schrieffer(BEC-BCS)crossover,by accurately tuning the magnetic field across the Feshbach resonance of lithium atoms.The magnetic field is calibrated by measuring the Zeeman shift of the optical transition.A non-monotonic anisotropic expansion is observed across the Feshbach resonance.The density distribution is explored in different interacting regimes,where a condensate of diatomic molecules forms in the BEC limit with the indication of a bimodal distribution.We also measure the three-body recombination atom loss in the BEC-BCS crossover,and find that the magnetic field of the maximum atom loss is in the BEC limit and gets closer to the Feshbach resonance when decreasing the atom temperature,which agrees with previous experiments and theoretical prediction.This work builds up a controllable platform for the study on the strongly interacting Fermi gas.     

用于原子干涉仪实验的锂原子的塞曼减速与磁光囚禁

为了制备适于原子干涉仪实验的低温锂原子样品,开展了锂原子的塞曼减速及与磁光阱囚禁相关的实验研究.设计并实现了一种结构紧凑的腔体内冷式多级线圈叠加的塞曼减速器,将速度小于600 m/s的7Li原子减速到60 m/s,磁光阱装载速率为5×108/s,囚禁原子数目1×109个,原子团的最低温度约为220±30μK.研究了光学黏胶中7Li原子的寿命与囚禁光频率失谐量的关系.这些结果为进一步开展7Li原子亚多普勒冷却、光势阱蒸发冷却以及原子干涉仪实验奠定了基础.