I was just reviewing some papers discussing Bose-einstein condensation, specifically "Creation of a Bose-condensed gas of 87Rb by laser cooling" by Hu et al., and I saw repeated references to the emergence of a "bimodal" velocity distribution being a hallmark of the BEC transition. However, I realized that none of the distributions look remotely bimodal, i.e. having two modes, i.e. prominent peaks or local maxima (See figure 2 here).
Trying to track this down a bit better, I realized that Wolfgang Ketterle's original paper also called their measured BEC velocity distribution bimodal (in the abstract no less!) (see figure 3 here).
As far as I can tell, with any reasonable reference to the normal definition of a "mode", all these distributions unambiguously have exactly 1 mode (at zero velocity), and are not bimodal. I get that the distribution is non-gaussian and that to fit the distribution they typically have a sum of two distributions, and maybe this is what they are trying to get at, but I feel that I'm missing something. What's "bimodal" about BEC velocity distributions?