Majorana quantization and half-integer thermal quantum Hall effect in a Kitaev spin liquid.

Area of Science:

• Condensed Matter Physics
• Quantum Magnetism
• Topological Phases of Matter

Background:

• The quantum Hall effect typically involves charge currents in 2D electron systems.
• Theoretical predictions suggested quantum Hall phenomena could arise from fractionalized quantum spins.
• Observation of spin-based quantum Hall quantization remained elusive until this study.

Purpose of the Study:

• To experimentally investigate the predicted quantum Hall effect arising from fractionalized quantum spins.
• To explore the properties of the Kitaev quantum spin liquid in alpha-RuCl3 under magnetic fields.
• To identify signatures of emergent Majorana fermions and their topological properties.

Main Methods:

• Utilized the two-dimensional quantum magnet alpha-RuCl3 with a dominant Kitaev interaction.
• Applied a magnetic field parallel to the sample to induce a quantum spin liquid state.
• Measured the two-dimensional thermal Hall conductance as a function of magnetic field at low temperatures.

Main Results:

• Observed a quantized plateau in the thermal Hall conductance, exactly half that of the integer quantum Hall effect.
• This half-integer quantization is attributed to chiral edge currents of charge-neutral Majorana fermions.
• Demonstrated spin fractionalization into Majorana fermions and Z2 fluxes, consistent with Kitaev quantum spin liquid theory.

Conclusions:

• The study provides the first experimental evidence of quantum Hall effect quantization from fractionalized quantum spins.
• The findings confirm the emergence of Majorana fermions in a quantum magnet, a key prediction of Kitaev spin liquids.
• This discovery has significant implications for understanding strongly correlated quantum matter and advancing topological quantum computing.