Physics Colloquium - Lauritsen Lecture

The advent of two-dimensional materials in recent years has opened up an emerging opportunity to design quantum metamaterials in which many-particle matter waves waves exhibit strongly-correlated and topologically non-trivial prroperties that are rare in naturally occuring crystals. For example, two-dimensional van der Waals crystals that are overlaid with a difference in lattice constant or a relative twist form a moiré pattern. In semiconductors and semimetals, the low-energy electronic properties of these systems are accurately described by Hamiltonians that have the periodicity of the moiré pattern – artificial crystals with lattice constants on the 10 nm scale. Over the past several years substantial progress has been made in the fabrication of these moire metamaterials, especially ones based on graphene, hexagonal boron nitride, and transitional metal dichalocogenides (TMDs). Since the miniband widths in both graphene and TMD moiré materials can be made small comparted to interaction energy scales, for different reasons [1,2] in the two cases, these materials can be used both for quantum simulation and for quantum design. An important property of moiré materials is that their band filling factors can be tuned over large ranges without introducing chemical dopants, simply by using electrical gates.

In addition to realizing Mott insulators, density waves, a vareity of different types of magnets, and superconductors – states of matter that are familiar from the study of strongly correlated atomic scale cyrstals – moire materials have emerged as perhaps the best plaform uncovered to date for studies of topologically non-trivial matter, especially strongly interacting topologically non-trivial matter. The role of band topology is natural in graphene moires, where it derives from the interesting band topology of graphene monolayers, but has been an unexpected bonus [3] in the case of TMD moires where it derives from twists in the layer degree of freedom. I will discuss the latest developments in this evolving story.

[1] R. Bistritzer, and A.H.MacDonald, Proceedings of the National Academy of Sciences 26, 12233 ( 2011).

[2] F. Wu, T. Lovorn, E. Tutuc, and A.H.MacDonald, Phys. Rev. Lett. 121, 026402 (2018).

[3] F. Wu, T. Lovorn, E. Tutuc, I. Martin, and A.H.MacDonald, Phys. Rev. Lett. 122, 086402 (2019).

Join via Zoom:
https://caltech.zoom.us/j/81866929019
Meeting ID: 818 6692 9019

The colloquium is held in Feynman Lecture Hall, 201 E. Bridge.