INSTABILITY AND STRATIFICATION OF A 2-COMPONENT BOSE-EINSTEIN CONDENSATE IN A TRAPPED ULTRACOLD GAS

The thermodynamic stability of a trapped Bose gas with a two-component condensate, e.g., a gas of atoms in two distinct hyperfine states or a binary gaseous mixture, is considered on the basis of modified Gross -Pitaevskii equations. Under certain conditions the system becomes uns table with respect to stratification, i.e., to spatial separation betw een the two condensates. One condensate assumes a donutlike spatial di stribution, while the other retains a centered distribution. Possible applications of the theory to recent experimental data on two overlapp ing condensates in Rb-87 are discussed.