  The discovery of robust transport via topological states in electronic,
photonic and phononic materials has deepened our understanding of wave
propagation in condensed matter with prospects for critical applications of
engineered metamaterials in communications, sensing, and controlling the
environment. Topological protection of transmission has been demonstrated in
the face of bent paths and on-site randomness in the structure. Here we measure
the propagation of microwave radiation in a topological medium possessing time
reversal symmetry with a cavity adjacent to the edge channel. A
coupled-resonance model analysis shows that the cavity is not a spin-conserving
defect and gives rise to negative time delay in transmission.
