Plots of the real (blue dots) and imaginary (red dots) parts of the valley kink states' eigenfrequencies at k y = 0 of a heterostructure with an armchair interface against the ratio between the nonreciprocal part C 2 and the reciprocal part C 1 of the NNN coupling. The blue and red regions denote the parity-time symmetric and parity-time symmetry-broken phases, respectively.
