  Fuzzy dark matter (FDM) is a compelling candidate for dark matter, offering a
natural explanation for the structure of diffuse low-mass haloes. However, the
canonical FDM model with a mass of $10^{-22}~{\rm eV}$ encounters challenges in
reproducing the observed diversity of dwarf galaxies, except for possibly
scenarios where strong galactic feedback is invoked. The introduction of
multiple-field FDM can provide a potential resolution to this diversity issue.
The theoretical plausibility of this dark matter model is also enhanced by the
fact that multiple axion species with logarithmically-distributed mass spectrum
exist as a generic prediction of string theory. In this paper we consider the
axiverse hypothesis and investigate non-linear structure formation in the
two-field fuzzy dark matter (2FDM) model. Our cosmological simulation with an
unprecedented resolution and self-consistent initial conditions reveals the
diverse structures of dark matter haloes in the 2FDM model for the first time.
Depending on the formation time and local tidal activities, late-time haloes
can host solitons of nested cores or solitons of one dominant species.
