Imaging work and dissipation in the quantum Hall state in graphene

Area of Science:

• Condensed Matter Physics
• Quantum Information Science

Background:

• Topological states offer global protection against local perturbations, crucial for quantum technologies.
• Dissipation in real devices often compromises theoretical topological protection, with microscopic origins being hard to study.

Purpose of the Study:

• To visualize and investigate microscopic dissipation mechanisms in graphene's quantum Hall state.
• To understand how these mechanisms undermine dissipationless transport and topological protection.

Main Methods:

• Utilized scanning nanothermometry for nanoscale thermal imaging.
• Employed simultaneous nanoscale thermal and scanning gate microscopy.
• Investigated edge reconstruction effects in graphene.

Main Results:

• Dissipation is driven by crosstalk between counterpropagating edge channels.
• Identified two distinct, spatially separated dissipation processes: elastic tunneling (affecting transport) and nonlocal inelastic scattering from defects (generating heat/entropy).
• Found that the primary work-generating process does not produce local heat, while heat generation occurs nonlocally.

Conclusions:

• The study reveals specific microscopic mechanisms limiting topological protection in quantum Hall states.
• Findings suggest strategies for engineering more robust quantum states for advanced device applications.
• Highlights the importance of understanding edge effects and defect scattering in topological systems.