SPICE Workshop on Quantum Matter for Quantum Technologies, May 21st - May 23rd 2024
Alexander Hamilton
The electronic properties of solids are determined by the crystal structure and interactions between electrons, giving rise to a variety of collective phenomena including superconductivity, strange metals and correlated insulators. The mechanisms underpinning many of these collective phenomena remain unknown, driving interest in creating artificial crystals which replicate the system of interest while allowing precise control of key parameters, such as cold atoms trapped in optical lattices, and Moiré superlattices in twisted two-dimensional (2D) materials.
Here we introduce an approach that allows lattices of arbitrary geometry to be created, incorporates long-range interactions, and enables direct transport measurements of the synthetic quantum matter. We superimpose a periodic electrostatic potential on the 2D electron gas in an ultra-shallow (25 nm deep) GaAs quantum well. The 100 nm period artificial crystal is identified by the formation of a new bandstructure, different from the original cubic crystal and unique to the artificial triangular lattice: transport measurements show the Hall coefficient changing sign as the chemical potential sweeps through the artificial bands. Uniquely, the artificial bandstructure can be continuously tuned from parabolic free-electron bands into linear graphene-like and flat kagome-like bands in a single device. The long lattice constant allows access to high magnetic fields with multiple flux quanta per unit cell (equivalent to thousands of Tesla in natural graphene), with clear evidence of many-body correlated states forming in the flat band.
This electrostatic gating technique is highly versatile and not material specific – it can be used with a multitude of semiconductors and atomically thin 2D materials. In the future it could be used to study collective quantum phenomena such as correlated insulators, topological systems (by introducing spin-orbit interactions), superconductivity, and magnetism in lattices of arbitrary geometry.