  Strong interactions and topology drive a wide variety of correlated ground
states. Some of the most interesting of these ground states, such as fractional
quantum Hall states and fractional Chern insulators, have fractionally charged
quasiparticles. Correlations in these phases are captured by the binding of
electrons and vortices into emergent particles called composite fermions.
Composite fermion quasiparticles are randomly localized at high levels of
disorder and may exhibit charge order when there is not too much disorder in
the system. However, more complex correlations were predicted when composite
fermion quasiparticles cluster into a bubble, then these bubbles order on a
lattice. Such a highly correlated ground state was termed the bubble phase of
composite fermions. Here we report the observation of this bubble phase of
composite fermions, evidenced by the reentrance of the fractional quantum Hall
effect. We associate this reentrance with a bubble phase with two composite
fermion quasiparticles per bubble. Our results demonstrate the existence of a
new class of strongly correlated topological phases driven by clustering and
charge ordering of emergent quasiparticles.
