Higher-order topological corner states induced solely by on-site potentials with mirror symmetry

Higher-order topological insulators have triggered a great deal of interest because they exhibit nontrivial bulk topology on lower-dimensional boundaries such as corners and hinges. While such interesting phases have been investigated in a plethora of systems by tuning staggered tunneling strength or manipulating existing topological phases, here we show that a higher-order topological phase can be driven solely by mirror-symmetric on-site potentials. We start with a chain model, and we show that it has nonzero edge states due to the lack of internal symmetries such as chiral and particle-hole symmetries. We then generalize the model to two dimensions, and we demonstrate the emergence of topological corner modes. These corner modes are an intrinsic manifestation of nontrivial bulk band topology protected by mirror symmetry, and thus they are robust against symmetry-preserved perturbations. Our model only requires the tuning of on-site energies, and it provides a realistic platform for studying a class of higher-order topological insulators using state-of-the-art experiment techniques.