From cavity-altered superconductivity to electrons in a moiré box: imaging the electronic structure of quantum materials

Electronic properties arise from phenomena at a multitude of length scales from sub-atomic to macroscopic. Atomic force microscopy (AFM) provides a multimodal lens on the rich electronic, magnetic, optical, and mechanical structure of quantum materials to bridge the gap between nanoscale local properties and global device properties. In this talk, I will discuss two recent experiments highlighting new phenomena made accessible by spatial imaging. In the first experiment, we ask whether the ground state of a material can be altered by engineering its electromagnetic environment. We resonantly couple superconductor k-(BEDT-TTF)2Cu[N(CN)2]Br (ET) to a cavity formed by a thin crystal of hexagonal boron nitride and observe an associated reduction in superfluid density. This experiment suggests that hBN/ET realizes a cavity-altered superconducting ground state and highlights the potential of dark cavities—devoid of external photons—for engineering quantum electronic ground states. In the second experiment, we ask how boundaries between regions of different stacking influence the electronic properties of moiré materials. In minimally twisted monolayer-bilayer graphene, we observe interference patterns arising from electronic confinement within rhombohedral and Bernal structural domains. As Landau levels form under magnetic field, these patterns evolve between regimes dominated by structural and magnetic confinement, at low and high field, respectively. These observations provide insight on the interplay between atomic and electronic structure in the wide variety of motifs accessible in moiré systems with more than two layers.

Tatiana will be at MPSD on Monday and Tuesday next week. Should you wish to schedule a discussion slot with her, please reach out to Michele Buzzi.