Superfluidity of Bose—Einstein condensates in ultracold atomic gases*
Zhu Qi-Zhonga), Wu Biaoa),b),c)†
       
Excitations along the x axis (the first column) and y axis (the second column) at different values of k . (a1,a2) k = 1; (b1,b2) k = 3; (c1,c2) k = 4. C 1 = 10, C 2 = 4, and γ = 1.