Hétor Ochoa

Abstract:

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.

References:

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

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

Short bio:

Héctor Ochoa is a theorist interested in problems at the intersection between hard and soft condensed matter physics. He completed his Ph D studies in Universidad Autónoma de Madrid in 2014, working in the group of Francisco Guinea. After that, Héctor moved to the University of California, Los Angeles, where he worked on spintronics in the group of Yaroslav Tserkovnyak. Since last November he is an Ikerbasque Research Fellow at DIPC in San Sebastian (Spain), and also an Adjunct Associate Research Scientist at Columbia University in New York (USA), where he has been working for the last three years.