  The realization of the quantum spin Hall effect in HgTe quantum wells has led
to the development of topological materials which, in combination with
magnetism and superconductivity, are predicted to host chiral Majorana
fermions. However, the large magnetization ($\sim$ a few tesla) in conventional
quantum anomalous Hall system, makes it challenging to induce
superconductivity. Here, we report two different emergent quantum Hall effects
in HgTe quantum wells dilutely alloyed with Mn. Firstly, a novel quantum Hall
state emerges from the quantum spin Hall state at an exceptionally low magnetic
field of $\sim 50$ mT. Secondly, tuning towards the bulk $p$-regime, we resolve
multiple quantum Hall plateaus at fields as low as $20 - 30$ mT, where
transport is dominated by a van Hove singularity in the valence band. These
emergent quantum Hall phenomena rely critically on the topological band
structure of HgTe and their occurrence at very low fields make them an ideal
candidate for interfacing with superconductors to realize chiral Majorana
fermions.

Mesoscale and Nanoscale Physics