Imaging inter-valley coherent order in magic-angle twisted trilayer graphene

Hyunjin Kim (), Youngjoon Choi, Étienne Lantagne-Hurtubise, Cyprian Lewandowski, Alex Thomson, Lingyuan Kong, Haoxin Zhou, Eli Baum, Yiran Zhang, Ludwig Holleis, Kenji Watanabe, Takashi Taniguchi, Andrea F. Young, Jason Alicea and Stevan Nadj-Perge ()
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Hyunjin Kim: California Institute of Technology
Youngjoon Choi: University of California, Santa Barbara
Étienne Lantagne-Hurtubise: California Institute of Technology
Cyprian Lewandowski: California Institute of Technology
Alex Thomson: California Institute of Technology
Lingyuan Kong: California Institute of Technology
Haoxin Zhou: California Institute of Technology
Eli Baum: California Institute of Technology
Yiran Zhang: California Institute of Technology
Ludwig Holleis: University of California, Santa Barbara
Kenji Watanabe: University of California, Davis
Takashi Taniguchi: National Institute for Materials Science
Andrea F. Young: National Institute for Materials Science
Jason Alicea: California Institute of Technology
Stevan Nadj-Perge: California Institute of Technology

Nature, 2023, vol. 623, issue 7989, 942-948

Abstract: Abstract Magic-angle twisted trilayer graphene (MATTG) exhibits a range of strongly correlated electronic phases that spontaneously break its underlying symmetries1,2. Here we investigate the correlated phases of MATTG using scanning tunnelling microscopy and identify marked signatures of interaction-driven spatial symmetry breaking. In low-strain samples, over a filling range of about two to three electrons or holes per moiré unit cell, we observe atomic-scale reconstruction of the graphene lattice that accompanies a correlated gap in the tunnelling spectrum. This short-scale restructuring appears as a Kekulé supercell—implying spontaneous inter-valley coherence between electrons—and persists in a wide range of magnetic fields and temperatures that coincide with the development of the gap. Large-scale maps covering several moiré unit cells further reveal a slow evolution of the Kekulé pattern, indicating that atomic-scale reconstruction coexists with translation symmetry breaking at a much longer moiré scale. We use auto-correlation and Fourier analyses to extract the intrinsic periodicity of these phases and find that they are consistent with the theoretically proposed incommensurate Kekulé spiral order3,4. Moreover, we find that the wavelength characterizing moiré-scale modulations monotonically decreases with hole doping away from half-filling of the bands and depends weakly on the magnetic field. Our results provide essential insights into the nature of the correlated phases of MATTG in the presence of strain and indicate that superconductivity can emerge from an inter-valley coherent parent state.

Date: 2023
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DOI: 10.1038/s41586-023-06663-8

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