Detecting Symmetry Breaking in Magic Angle Graphene Using Scanning Tunneling Microscopy

A growing body of experimental work suggests that magic angle twisted bilayer graphene exhibits a cascade of spontaneous symmetry-breaking transitions, sparking interest in the potential relationship between symmetry breaking and superconductivity. However, it has proven difficult to find experimental probes which can unambiguously identify the nature of the symmetry breaking. Here, we show how atomically resolved scanning tunneling microscopy can be used as a fingerprint of symmetry-breaking order. By analyzing the pattern of sublattice polarization and Kekule distortions in small magnetic fields, order parameters for each of the most competitive symmetry-breaking states can be identified. In particular, we show that the Kramers intervalley coherent state, which theoretical work predicts to be the ground state at even integer fillings, shows a Kekule distortion which emerges only in a magnetic field.

Automated summary

Experimental works have shown that magic angle twisted bilayer graphene exhibits spontaneous symmetry-breaking transitions, and scientists have identified competitive symmetry-breaking states by analyzing sublattice polarization and Kekule distortions in scanning tunneling microscopy.