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Carbon with a twist: The physics of Moiré-patterned graphene bilayers

When Sep 18, 2019
from 12:45 pm to 02:00 pm
Speaker Hector Ochoa de Eguileor Romillo
Speaker Information Columbia University
Where 1311 HN
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Van der Waals materials like graphite are formed from weakly interacting and mechanically stiff atomic layers. Sliding and twisting these layers with respect to each other give rise to superstructures with new physics, such as the plethora of strongly correlated phenomena observed in slightly twisted graphene layers [1]. The prominence of electronic correlations in this system is ultimately linked to the formation of very narrow bands due to interference in a long-scale Moiré pattern. In this talk, I will review the phenomenology of twisted bilayer graphene as revealed by scanning tunneling microscopy and transport measurements and some of the theoretical models in the recent literature. These experimental results suggest a rich phase diagram, although sensitive to details of the device, which combines features of different correlated systems like high-Tc superconductors and quantum Hall ferromagnets. In my exposition, I would emphasize usually overlooked aspects associated with the lack of periodicity for generic twist angles, such as the emergence of new collective modes, phasons [2], and their connection with the widespread presence of twist angle disorder in the samples.

[1] Y. Cao et al., Nature 556, 43; ibid., 80 (2018).
[2] H. Ochoa, arXiv:1905.10850.

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