We prove that if the boundary of a topological insulator divides the plane into two regions,
each containing arbitrarily large balls, then it acts as a conductor. Conversely, we construct a …

In space-adiabatic approaches one can approximate Hamiltonians that are modulated
slowly in space by phase-space functions that depend on position and momentum. In this …

A typical crystal is a finite piece of a material which may be invariant under some point
symmetry group. If it is a so-called intrinsic higher-order topological insulator or …