Magnetic Breakdown In Artificial Superlattices

Artificial superlattices are systems in which a periodic potential is imposed over the top of a two dimensional electron gas. This can be done either optically, via electrostatic gating or via moire effects with lattice constants that are typically much larger than atomic crystals. The electronic band structure of these systems can be engineered by varying the lattice pattern and by tuning its strength. In particular, artificial graphene (AG), an artificial lattice with triangular symmetry, aims to simulate the electronic properties of graphene, namely its two Dirac cones. It has been shown, theoretically, that AG can also carry a flat band. Thus there is a desire to understand experimental realizations of AG . While the interesting properties of AG are peculiar to the strong modulation regime it is possible to characterize real devices through studies of the weak modulation regime.

If, in addition to the superlattice modulation, we add a weak magnetic field the electrical resistance will oscillate with different frequency components corresponding to different closed segments of the Fermi surface. Magnetic breakdown refers to the possibility of electrons tunneling between different orbits. This gives rise to many possible electron trajectories and hence many possible frequencies in the resistivity. In this work we characterize, using the magnetic breakdown concept, a set of experimentally observed resistivity oscillations in a weakly modulated triangular superlattice system. Further, we discuss how this analysis could be used to characterize the modulation strength of real artificial superlattices.

About the presenter

Zeb Krix is a PhD student at UNSW, where he studies the theory behind artificial graphene and artificial topological insulators, which are 2D materials with an imposed superlattice structure. Zeb models such systems in the presence of a perpendicular magnetic field in order to improve understanding of the relevant electronic transport measurements. This work is closely linked with experimental work conducted by FLEET’s Daisy Wang, Oleh Klochan and Alex Hamilton, and is part of FLEET’s Research theme 1: Topological materials. and Research theme 3 light transformed materials.