Comment on ``Nonlinear band structure in Bose-Einstein condensates: Nonlinear Sch\"odinger equation with a Kronig Penney potential"

In their recent paper [Phys. Rev. A 71, 033622], B. T. Seaman et al. studied Bloch states of the condensate wave function in a Kronig-Penney potential and calculated the band structure. They argued that the effective mass is always positive when a swallow-tail energy loop is present in the band structure. In this comment, we reexamine their argument by actually calculating the effective mass. It is found that there exists a region where the effective mass is negative even when a swallow-tail is present. Based on this fact, we discuss the interpretation of swallow-tails in terms of superfluidity.Comment: 3 pages, 3 figure

光格子中のボース-アインシュタイン凝縮体に関する理論的研究

制度:新 ; 文部省報告番号:甲2051号 ; 学位の種類:博士(理学) ; 授与年月日:2005/3/15 ; 早大学位記番号:新400