MSE Seminar: Aaron Sharpe

Event interval: Single day event
Campus location: Bagley Hall (BAG)
Campus room: 154
Accessibility Contact: Matthew Yankowitz, myank@uw.edu
Event Types: Lectures/Seminars

Title: Quantum Electronic Phases in Twisted Trilayer Graphene

Abstract: Stacking layers of van der Waals materials with an interlayer twist modulates interlayer hopping on the moiré length scale, enabling control over electronic band structure. We can extend upon this paradigm by introducing a third twisted layer. The system now contains two interfering moiré patterns that modulate the effective local electronic properties on a longer supermoiré length scale. Here, I will provide two vignettes about the supermoiré system of twisted trilayer graphene. Together, these studies establish an organizing framework for the correlated phases in twisted trilayer graphene. They reveal a direct correspondence between superconductivity and thermodynamic signatures of electronic correlations. Additionally they suggest a sensitive interplay of the supermoiré modulation and lattice relaxation that dictates the resultant phenomenology.

First, we will focus on a narrow region of the ‘angle-angle’ space that determines this trilayer structure. Using a scanning single-electron transistor, we map the impact of electron-electron interactions as a function of twist angle in the sample. We observe gapped correlated insulators and a ‘sawtooth’ in electronic compressibility. Subsequent transport measurements in the same region reveal robust superconductivity. Our measurements indicate that superconductivity is not directly tied to the correlated insulators. Rather, its critical temperature correlates closely with the strength of the sawtooth in compressibility, possibly suggesting a common origin or link between the two.

Second, I will discuss how the electronic phases evolve across a broad range of twist angles whose twist angles lie along two continuous lines in the twist-angle parameter space. Different points along these lines exhibit differing phenomenology, pointing to other variables beyond twist-angle. Theoretical calculations that lattice relaxation in twisted trilayer graphene depends sensitively on both the magnitude and the relative handedness of the angles.

Bio: Dr. Aaron Sharpe is an Associate Scientist at SLAC National Laboratories and Stanford University, having received his Ph.D. in Applied Physics from Stanford University in 2020 and following a Truman Fellowship at Sandia National Laboratories from 2020 to 2023. Aaron has made a number of key contributions to the world of van der Waals systems, including the discovery of orbital ferromagnetism in twisted bilayer graphene for which he was awarded UIUC's prestigious McMillan award. His work further includes some of the first evidence of strong correlations in rhombohedral graphene systems. At present, Aaron focuses on exploring strong correlations in various trilayer moiré systems and rhombohedral graphene systems in the absence of a moiré potential.