Schedule Dec 07, 2020
Moire nematic phase in twisted double bilayer graphene
Carmen Rubio-Verdú, Columbia
Cite as: doi:10.26081/K62W3K

In van der Waals structures, moiré superlattices give rise to electronic flat bands, setting the stage for emergent collective phenomena, such as correlated insulating and superconducting states in twisted bilayer graphene. Such phenomenology may also be present in higher order heterostructures where the vertical stacking order plays a major role. Recent transport measurements showed that the system formed by two Bernal-stacked graphene bilayers rotated with respect to each other ~1.3° hosts correlated insulating states when its energy band is filled with electrons. In this talk I will present real-space imaging of such double bilayer moiré superstructures. Scanning Tunneling Spectroscopy reveals the presence of sharp resonances in the density of states, whose spatial distribution within the moiré unit cell is governed by their inequivalent stacking arrangement. Tuning the electron filling as well as the displacement field reveals broken C3 symmetry that emerges when the Fermi level is brought in the flat band. This symmetry breaking is manifested as long-range commensurate stripes along a high-symmetry moiré crystallographic direction, distinctive of nematic correlations of electronic origin. Comparing our experimental data with a combination of microscopic and phenomenological modeling, we show that the nematic instability is not associated with the local scale of the graphene lattice, but is an emergent phenomenon at the scale of the moiré lattice, pointing to the universal caracter of this ordered state in flat band moiré materials.

To download: Right-click and choose "Save Link As..."