  We report a magneto-induced topological phase transition in inverted
InAs/GaSb bilayers from a quantum spin Hall insulator to a normal insulator. We
utilize a dual-gated Corbino device in which the degree of band inversion, or
equivalently the electron and hole densities, can be continuously tuned. We
observe a topological phase transition around the magnetic field where a band
crossing occurs, that is accompanied by a bulk-gap closure characterized by a
bulk conductance peak (BCP). In another set of experiments, we study the
transition under a tilted magnetic field (tilt angle $\theta$). We observe the
characteristic magneto-conductance around BCP as a function of $\theta$, which
dramatically depends on the density of the bilayers. In a relatively
deep-inversion (hence a higher density) regime, where the electron-hole
hybridization dominates the excitonic interaction, the BCP grows with $\theta$.
On the contrary, in a shallowly-inverted (a lower density) regime, where the
excitonic interaction dominates the hybridization, the BCP is suppressed
indicating a smooth crossover without a gap closure. This suggests the
existence of a low-density, correlated insulator with spontaneous symmetry
breaking near the critical point. Our highly controllable electron-hole system
offers an ideal platform to study interacting topological states as proposed by
recent theories.
