Circuit implementation of a four-dimensional topological insulator

Published in Nature Communications, 2020

You Wang, Hannah M. Price, Baile Zhang and Y. D. Chong
Nature Communications 11, 2356 (2020)

https://www.nature.com/articles/s41467-020-15940-3

https://arxiv.org/abs/2001.07427

The classification of topological insulators predicts the existence of high-dimensional topological phases that cannot occur in real materials, as these are limited to three or fewer spatial dimensions. We use electric circuits to experimentally implement a four-dimensional (4D) topological lattice. The lattice dimensionality is established by circuit connections, and not by mapping to a lower-dimensional system. On the latticeā€™s three-dimensional surface, we observe topological surface states that are associated with a nonzero second Chern number but vanishing first Chern numbers. The 4D lattice belongs to symmetry class AI, which refers to time-reversal-invariant and spinless systems with no special spatial symmetry. Class AI is topologically trivial in one to three spatial dimensions, so 4D is the lowest possible dimension for achieving a topological insulator in this class. This work paves the way to the use of electric circuits for exploring high-dimensional topological models.