Exceptional points in negatively refracting chirowaveguides due to giant chirality

In non-Hermitian systems, particularly those adhering to $\mathcal{PT}$ symmetry, exceptional points (EPs) are critical junctures wherein eigenvalues and eigenvectors coalesce. These points induce the convergence of eigenmodes in waveguiding systems, resulting in unique dispersion features and remarkable effects such as slow light. In a configuration comprising two coupled waveguides, EPs can be achieved via mechanisms involving balanced gain-loss modulation or contradirectional modal interference. By leveraging the latter, in homogeneous chirowaveguides without any reliance on periodicity, we demonstrate the signature phase transitions induced by negative refraction due to giant chirality, which does not necessitate the simultaneous negativity of the permittivity and permeability. Our approach offers advantages over traditional $\mathcal{PT}$-symmetric and negative-refractive-index waveguides, as it does not pose the manufacturing difficulties of balancing the creation and absorption of photons while providing opportunities for remarkable light manipulation due to the presence of chirality. Experimental implementations of metamedia with giant and, moreover, controllable chirality indicate that our medium is well within reach of current technology.