Allan MacDonald (U Texas Austin), Moiré Patterns   in Two-Dimensional Materials

Date: Thu. April 18th, 2019, 4:00 pm-5:00 pm
Location: Rockefeller 301

Moiré Patterns   in Two-Dimensional Materials

According to Wikipedia a moiré pattern (/mwɑːrˈeɪ/; French: [mwaˈʁe]) is a large scale interference pattern that is produced when an opaque regular pattern with transparent gaps is overlaid on another similar pattern with a different pitch or orientation.  Moiré patterns are ubiquitous in two-dimensional van der Waals materials in which the regular patterns are formed by two-dimensional crystals, differences in pitch are established by differences in lattice constants and differences in orientation, which can be controlled experimentally.  The electronic properties of two-dimensional semiconductor, gapless semiconductor, and semimetal systems in which moiré patterns have been established have continuum model Hamiltonians with the periodicity of the moiré pattern.  I will discuss some examples [2,3,4] of new physics that can be explored using van der Waals material moiré patterns, comment on the recent discovery [5] of superconductivity in magic angle twisted bilayer graphene, and speculate on interesting future directions.

 

 

[1] Moire bands in twisted double-layer graphene, R. Bistritzer and A.H. MacDonald, PNAS 108, 12233 (2011).

[2] Fractional Hofstadter States in Graphene on Hexagonal Boron Nitride, Ashley M. DaSilva, Jeil Jung, and A.H. MacDonald, Phys. Rev. Lett. 117, 036802 (2016).

[3] Topological Exciton Bands in Moiré Heterojunctions, Fengcheng Wu, Timothy Lovorn, and A.H. MacDonald, Phys. Rev. Lett. 118, 14701 (2017).

[4] Theory of phonon-mediated superconductivity in twisted bilayer graphene, Fengcheng Wu, A.H. MacDonald, and I. Martin, Phys. Rev. Lett. 121, 257001 (2018).

 [5]  Magic-angle graphene superlattices: a new platform for unconventional superconductivity,  Y. Cao et al. Nature (2018).