  While in the lowest Landau level the electron-electron interaction leads to
the formation of the Wigner crystal, in higher Landau levels a solid phase with
multiple electrons in a lattice site of crystal was predicted, which was called
the bubble phase. Reentrant integer quantum Hall states are believed to be the
insulating bubble phase pinned by disorder. We carry out nonlinear transport
measurements on the reentrant states and study the de-pinning of the bubble
phase, which is complementary to previous microwave measurements and provides
unique information. In this study, conductivity is directly measured with
Corbino geometry. Based on the threshold electric field of de-pinning, a phase
diagram of the reentrant state is mapped. We discuss an interaction-driven
topological phase transition between the integer quantum Hall state and the
reentrant integer quantum Hall state.
