  We present the new concept of photonic alloy as a non-periodic topological
material. By mixing non-magnetized and magnetized rods in a non-periodic 2D
photonic crystal configuration, we realized photonic alloys in the microwave
regime. Our experimental findings reveal that the photonic alloy sustains
non-reciprocal chiral edge states (CESs) even at very low concentration of
magnetized rods. The non-trivial topology and the associated edge states of
these non-periodic systems can be characterized by the winding of the
reflection phase. Our results indicate that the threshold concentrations for
the investigated system within the first non-trivial band gap to exhibit
topological behavior approach zero in the thermodynamic limit for
substitutional alloys, while the threshold remains non-zero for interstitial
alloys. At low concentration, the system exhibits an inhomogeneous structure
characterized by isolated patches of non-percolating magnetic domains that are
spaced far apart within a topologically trivial photonic crystal. Surprisingly,
the system manifests CESs despite a local breakdown of time-reversal symmetry
rather than a global one. Photonic alloys represent a new category of
disordered topological materials, offering exciting opportunities for exploring
topological materials with adjustable gaps.
