Double-flattop quantum droplets in low-dimensional Bose-Bose mixtures

We predict the existence of double-flattop quantum droplets in atomic Bose-Bose mixtures. Solutions of this type have two flattop regions of nearly uniform atomic density corresponding to a compressed central core surrounded by a rarefied layer. The birth of these double-flattop quantum droplets is analytically described using a perturbation theory, which in the leading order reduces the problem to the cubic nonlinear Schr\"odinger equation. Its properties are then used to predict the shape of double-flattop solutions and draw the conclusions about their stability. The analytical results apply to one- and multidimensional quantum droplets, provided that the energy density satisfies certain conditions. Using the numerical continuation from the asymptotic limit, we obtain the families of one- and two-dimensional double flattop quantum droplets and confirm the stability of the nodeless states of this type.