  Higher-order topological insulators have triggered great interests because of
exhibitions of non-trivial bulk topology on lower-dimensional boundaries like
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 onsite potentials. We first introduce
a simple chain model in one dimension that mimics the Su-Schrieffer-Heeger-like
model. However, due to the lack of internal symmetries like chiral or
particle-hole symmetry, the energies of the topological edge modes are not
pinned at zero. Once the model is generalized to two dimensions, we observe the
emergence of topological corner modes. These corner modes are intrinsic
manifestation of non-trivial bulk band topology protected by mirror symmetry,
and thus, they are robust against symmetry-preserved perturbations. Our study
provides a concise proposal for realizing a class of higher-order topological
insulators, which involves only tuning onsite energies. This can be easily
accessible in experiments and provides a different playground for engineering
topological corner modes.
