Floquet second-order topological insulators from nonsymmorphic space-time symmetries

Understand

We propose a systematic way of constructing Floquet second-order topological insulators (SOTIs) based on time-glide symmetry, a nonsymmorphic space-time symmetry that is unique in Floquet systems.

• In particular, we are able to show that the static enlarged Hamiltonian in the frequency domain acquires the reflection symmetry, which is inherited from the time-glide symmetry of the original system.
• As a consequence, one can construct a variety of time-glide symmetric Floquet SOTIs using the knowledge of static SOTIs.
• Moreover, the time-glide symmetry only needs to be implemented approximately in practice, enhancing the prospects of experimental realizations.