Uncovering the spin ordering in magic-angle graphene via edge state equilibration

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Magic-angle twisted bilayer graphene (MATBG) exhibits flat bands, enabling the study of interaction-driven ground states.
• Previous research identified correlated insulators and excitations in MATBG at specific filling factors.
• The spin-valley polarization of topological states in MATBG at high magnetic fields remains largely unexplored.

Purpose of the Study:

• To investigate the spin polarization of topological states in MATBG under high magnetic fields.
• To develop and apply a novel technique for measuring electronic band structure and edge mode spin polarization.
• To determine the spin polarization of symmetry-broken quantum Hall states and correlated Chern insulators in MATBG.

Main Methods:

• Development of a technique utilizing twist-decoupled van der Waals layers.
• Measurement of the electronic band structure of MATBG.
• Analysis of backscattering between counter-propagating edge states to determine relative spin polarization.

Main Results:

• Symmetry-broken quantum Hall states extending from the charge neutrality point in MATBG were found to be spin unpolarized at even integer filling factors.
• The correlated Chern insulator emerging from half filling of the flat valence band was also found to be spin unpolarized.
• Evidence suggests that the conduction band counterpart of the Chern insulator may be spin polarized.

Conclusions:

• The study provides crucial insights into the spin properties of topological states in MATBG.
• The developed technique offers a new pathway for probing spin polarization in moiré materials.
• Understanding spin polarization is key to harnessing MATBG for future electronic and spintronic applications.