Matthew Yankowitz, Tunable correlated and topological states in twisted graphene heterostructures, University of Washington
Zoom Details
Seminar
2:00 pm - 3:00 pm
Zoom Link: https://ucsb.zoom.us/j/82009498038?pwd=L2YxZFBQRkx3aVBOYWJXaTJQTWgvdz09
Meeting ID: 820 0949 8038 and Password: qfSeminar
Speaker
Matthew Yankowitz
Physics Department
Washington University
Bio
Matthew Yankowitz is an Assistant Professor of Physics at the University of Washington, with a joint appointment in the Department of Materials Science and Engineering. He received his B.S. in Physics from Stanford University in 2011, and his Ph.D. in Physics in Prof. Brian LeRoy’s group at the University of Arizona in 2015. He subsequently performed his postdoctoral work in Prof. Cory Dean’s group at Columbia University and joined UW as an Assistant Professor in 2019. Research in Matt’s group at UW focuses the investigation and control of topology, correlations, and magnetism in 2D van der Waals heterostructures using a combination of electrical transport and scanning probe microscopy.
Abstract
In van der Waals heterostructures composed of two rotated graphene sheets, a moiré superlattice results in the emergence of flat electronic bands over a small range of twist angles. A variety of highly tunable correlated and topological states have recently been identified in these platforms owing to the quenched kinetic energy of charge carriers and the intrinsic Berry curvature of the flat bands. I will discuss our recent work investigating these states in three different twisted graphene platforms. In twisted bilayer graphene – two rotated monolayer graphene sheets – we observe correlated insulating states and superconductivity for twist angles very near 1.1°. These states are exquisitely sensitive to the twist angle, and can be further tuned dynamically within a single device by electrostatic doping or with hydrostatic pressure. In twisted double bilayer graphene – two rotated sheets of Bernal-stacked bilayer graphene – correlated states can be additionally controlled by an external electric field, and consequently manifest over a wider range of twist angles. Finally, in twisted monolayer-bilayer graphene, we observe a novel form of ferromagnetism driven primarily by the formation of spontaneous orbital currents rather than the ordering of electron spins. Owing to the non-trivial topology of the bands, the orbital ferromagnetism is sometimes accompanied by signatures of an incipient quantum anomalous Hall state, although the phase diagram depends sensitively on the twist angle. Overall, our results demonstrate the extraordinary tunability of correlated and topological states in twisted graphene heterostructures.
