Emergent quantum Hall effects below 50 mT in a two-dimensional topological insulator

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Physics

Background:

• The quantum spin Hall effect in HgTe quantum wells established topological materials.
• Combining topological materials with magnetism and superconductivity could host chiral Majorana fermions.
• Conventional quantum anomalous Hall systems face challenges in inducing superconductivity due to large magnetization.

Purpose of the Study:

• To report emergent quantum Hall effects in (Hg,Mn)Te quantum wells.
• To investigate phenomena at exceptionally low magnetic fields.
• To explore potential for realizing chiral Majorana fermions.

Main Methods:

• Fabrication and characterization of (Hg,Mn)Te quantum wells.
• Measurement of quantum Hall effect under low magnetic fields.
• Analysis of transport properties influenced by topological band structure and van Hove singularities.

Main Results:

• Observation of a novel quantum Hall state emerging from the quantum spin Hall state at ~50 mT.
• Resolution of quantum Hall plateaus at 20-30 mT in the bulk p-regime, dominated by a van Hove singularity.
• Demonstration that these emergent phenomena depend critically on the topological band structure of HgTe.

Conclusions:

• Emergent quantum Hall effects were observed in (Hg,Mn)Te quantum wells at very low magnetic fields.
• These findings offer a new pathway for studying topological materials.
• The low-field phenomena present an ideal platform for the realization of chiral Majorana fermions.