Strangeness from electron-phason scattering in moiré superlattices

DIPC Seminars

Héctor Ochoa
Columbia University, USA
Hybrid Seminar: Donostia International Physics Center
Andres Arnau
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Strangeness from electron-phason scattering in moiré superlattices

In this talk I will explain why I believe that the large, linearin-T resistivity observed in twisted bilayer graphene down to very low temperatures (as low as 50-60 mK) can be explained by scattering of electrons with phason modes of the incommesurate moiré superlattice. This scenario contains features common to the other two agents usually invoked to explain the phenomenology: phonons and quantum critical fluctuations. Phasons are similar to acoustic phonons, but contrary to true Goldstone modes, their dynamics are not protected by a microscopic symmetry. Consequently, they are overdamped at long wavelengths, reflecting that in this regime the moiré pattern relaxes via internal diffusive processes rather than by collective oscillations as a result of the friction between the layers. The associated transfer of phason spectral weight to low energies makes phason scattering a very efficient channel for entropy production at low temperatures. In particular, the electronic resistivity is linear down to a new temperature scale lower than the Bloch-Grüneisen scale defined by kinematics on the Fermi surface. Phasons should also dominate other thermodynamic and transport properties at low temperatures such as the specific heat or the thermal conductivity.