"QUANTUM MATERIALS AND DEVICES SEMINARS: "Carbon with a twist: electrons and phonons in moiré graphene bilayers""

Who: Hector Ochoa, Columbia University, USA

Place: Online Seminar, Donostia International Physics Center

Date: Wednesday, 15 September 2021, 15:00

Sliding and twisting the layers of Van der Waals materials give rise to superstructures with new physics, such as the plethora of strongly correlated phenomena (superconductivity included) observed in twisted bilayer graphene. In this talk, I will review our current understanding of how electrons behave in moiré patterns, and how disorder and phonons may affect this behavior. I will argue that the long-wavelength dynamics of these generically incommensurate structures are dominated by new collective modes: phasons [1]. These modes correspond to coherent superpositions of optical phonons describing the sliding motion of stacking domain walls separating regions of partial interlayer commensuration. I will discuss various physical consequences of this observation, including the widespread presence of structural disorder in the form of strain accumulated between the layers [2]. At neutrality, these tensions favor orbital magnetic order with charged vortex excitations [3], which may explain some of the disparities observed in transport measurements in different devices.

[1] H. Ochoa, Phys. Rev. B 100, 155426 (2019).
[2] H. Ochoa and R. M. Fernandes, arXiv:2108.10342.
[3] H. Ochoa, Phys. Rev. B 102, 201107 (2020).

Host: Miguel A. Cazalilla


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