Visualizing Gate-tunable Nanoscale Chladni Patterns in Dirac Billiards: Nano Seminar Series

Seminar | October 13 | 2-3 p.m. | 180 Tan Hall

 Prof. Jairo Velasco, Jr., UC Santa Cruz, Physics

 Berkeley Nanosciences and Nanoengineering Institute

Dirac fermions have coexisting electron-hole states and exhibit angular anisotropy when transmitting through a potential barrier. Because of these attributes, electrostatically confined Dirac fermions are fundamentally different from similarly trapped Schrödinger fermions. In particular, these confined charge carriers are predicted to exhibit new states with properties that depend strongly on their angular momentum, the integrability of their confinement potential, and whether they are massless or massive.

Several recent experiments have investigated confined states within integrable structures for massless Dirac fermions. However, the spatial behavior of states with high angular momentum and within non-integrable structures remains unexamined. In addition, experiments on confined massive Dirac fermions are lacking despite numerous intriguing theoretical predictions for these charge carriers.

In this talk I will discuss experiments that use scanning tunneling microscopy (STM) to map the behavior of electrostatically confined Dirac fermions at the nanoscale. Our confinement potentials were realized by manipulating defect charge within boron nitride (BN) crystals to create pn junctions on graphene (or bilayer graphene)/BN heterostructures.

First, for circular graphene pn junctions we resolved Chladni-like figures by accessing high angular momentum states. Subsequently, by merging three of these circular pn junctions we realized a stadium structure and observed quantum interference patterns that are vastly different from circularly confined Dirac fermions. Finally, by using pn junctions on bilayer graphene/BN heterostructures, we imaged the response of electrostatically confined massive Dirac fermions.

The techniques and findings presented here open the door to highly controlled studies on the ergodicity of confined Dirac fermions—gate tunable Dirac billiards.