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

TL;DR

This paper investigates how large in-plane magnetic fields induce a semi-metallic phase in inverted HgTe quantum wells, revealing a transition characterized by decreasing magnetoresistance and a resistance upturn beyond a critical field.

Contribution

It provides experimental evidence of a field-induced gapless semi-metallic phase in inverted HgTe quantum wells and supports classical two-carrier transport models for the observed phenomena.

Findings

Magnetoresistance decreases monotonically up to 10 T in inverted HgTe wells.

A critical in-plane magnetic field $B_c$ induces a gapless semi-metallic phase.

Beyond $B_c$, resistance shows a strong upturn consistent with two-carrier transport theory.

Abstract

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 is applied. We show that in quantum wells with inverted band structure a monotonically decreasing magnetoresistance is observed when a magnetic field up to order 10 T is applied parallel to the quantum well plane. This feature is accompanied by a vanishing of non-locality 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 semi-metallic region beyond the known regime. After an initial saturation phase in the presumably gapless phase, we observe a strong upturn of the longitudinal resistance. A small residual Hall signal picked up in non-local measurements suggests that this feature is likely a bulk phenomenon and caused by the semi-metallicity 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.