Tunable three-way topological energy-splitter

Strategically combining four structured domains creates the first ever three-way topological energy-splitter; remarkably, this isonly possible using a square, or rectangular, lattice, and not the graphene-like structures more commonly used in valleytronics.To achieve this effect, the two mirror symmetries, present within all fully-symmetric square structures, are broken; this leads totwo nondistinct interfaces upon which valley-Hall states reside. These interfaces are related to each other via the time-reversaloperator and it is this subtlety that allows us to ignite the third outgoing lead. The geometrical construction of our structuredmedium allows for the three-way splitter to be adiabatically converted into a wave steerer around sharp bends. Due tothe tunability of the energies directionality by geometry, our results have far-reaching implications for applications such asbeam-splitters, switches and filters across wave physics