Magnetoresistance in the in-plane magnetic field induced semimetallic phase of inverted HgTe quantum wells

In this study we have measured the magnetoresistance response of inverted HgTe quantum wells in the presence of a large parallel magnetic field up to 33 T. We show that in quantum wells with inverted band structure a monotonically decreasing magnetoresistance is observed when a magnetic field up to the order of 10 T is applied parallel to the quantum well plane. This feature is accompanied by a vanishing of nonlocality and is consistent with a predicted modification of the energy spectrum that becomes gapless at a critical in-plane field B-c. Magnetic fields in excess of B-c allow us to investigate the evolution of the magnetoresistance in this field-induced semimetallic region beyond the known regime. After the longitudinal resistance reaches a minimum in the presumably gapless phase, we observe a strong upturn of the longitudinal resistance. A small residual Hall signal picked up in nonlocal measurements suggests that this feature is likely a bulk phenomenon and is caused by the semimetallicity of the sample. Theoretical calculations indeed support that the origin of these features is classical and a power law upturn of the resistance can be expected due to the specifics of two-carrier transport in thin (semi)metallic samples subjected to large magnetic fields.