IFIMAC+ICMM Joint Seminar Series focuses on cutting-edge research on condensed matter physics, bringing speakers from all over the world to our Cantoblanco Campus. All talks are streamed online. Some of them will be celebrated on campus and onsite participation will also be possible. You need to subscribe to our mailing list at the link provided below to get the links to the seminar room. https://listas-correo.uam.es/sympa/subscribe/seminarios-ifimac-icmm-l

«Phase» fluctuations of moiré superlattices

Héctor Ochoa, Donostia International Physics Center (Spain) and Columbia University in New York (USA)

Janurary 20th (Thursday), 2022, 12:00 CET (hybrid. Onsite @ ICMM-CSIC)

In this talk I will argue that the long-wavelength dynamics of moiré superlattices is more akin to a fluid than to a solid. The reason is the appearance of soft collective modes, called phasons, associated with the sliding motion of one layer with respect to the other [1]. This motion necessarily involves friction (microscopically, due to anharmonic coupling with “amplitude” modes). Consequently, phasons are overdamped at low frequencies, reflecting that in this regime the moiré pattern relaxes via internal diffusive processes rather than by collective oscillations [2]. I will discuss physical consequences of this observation for twisted bilayer graphene, including the widespread presence of “twist angle disorder”. In particular, I will show that, regardless of the specific form of disorder, fluctuations in twist angle are determined by the collective pinning of stacking domain walls caused by lattice relaxation.


[1] H. Ochoa, Phys. Rev. B 100, 155426 (2019).

[2] H. Ochoa and R. M. Fernandes, arXiv:2108.10342.