Topological phase transitions and a spin-related metallic state in inverted HgTe quantum wells under in-plane magnetic field

We show that in inverted HgTe quantum wells, the application of a strong in-plane magnetic field restores the normal sequence of the subbands, thus transforming the system from a topological insulator into a normal insulator phase. The transformation consists of two consecutive quantum phase transitions due to the large Zeeman splitting of electron states. On the other hand, due to the negligible Zeeman splitting of hole states, the intermediate phase between the transitions is semimetallic. Both phase transitions and the semimetallic phase have already been observed, and our theory allows for a consistent interpretation of the experimental results.