Intrinsic quantized anomalous Hall effect in a moiré heterostructure.

Area of Science:

• Condensed matter physics
• Materials science
• Quantum phenomena

Background:

• The quantum anomalous Hall (QAH) effect is a topological phenomenon combining topology and magnetism, resulting in quantized Hall resistance at zero magnetic field.
• Previous studies often relied on magnetically doped systems, which have limitations in stability and energy gap characteristics.

Purpose of the Study:

• To report the observation of the QAH effect in a novel material system: twisted bilayer graphene aligned to hexagonal boron nitride.
• To investigate the underlying mechanisms and characteristics of the QAH effect in this system, particularly focusing on intrinsic interactions and magnetic ordering.

Main Methods:

• Fabrication of twisted bilayer graphene precisely aligned with hexagonal boron nitride.
• Transport measurements to observe quantized Hall resistance at zero magnetic field.
• Characterization of the material's magnetic properties and energy gap in relation to temperature and magnetic ordering.

Main Results:

• Observation of the QAH effect driven by intrinsic strong interactions, polarizing electrons into a single spin- and valley-resolved moiré miniband with Chern number C = 1.
• The measured transport energy gap exceeds the Curie temperature, indicating robust magnetic ordering.
• Precise quantization of Hall resistance (within 0.1% of the von Klitzing constant) persists to several Kelvin at zero magnetic field.
• Electrical currents as low as 1 nanoampere can controllably switch the magnetic order, enabling rewritable magnetic memory.

Conclusions:

• Twisted bilayer graphene aligned to hexagonal boron nitride is a viable platform for realizing the quantum anomalous Hall effect.
• The observed effect is robust, with a significant energy gap and persistent quantization at higher temperatures and zero magnetic field.
• The material's ability to be electrically switched opens possibilities for developing novel, high-density, and low-power magnetic memory devices.