Fig. 4: Observation of EPs, of their topological charges and of their annihilation.
From: Annihilation of exceptional points from different Dirac valleys in a 2D photonic system
Theoretical figures are obtained by diagonalizing the Hamiltonian (2) with parameters obtained from the sample 1 and given in Methods. The procedure for the extraction of experimental energies is detailed in Methods. a–d Difference of the real part of the eigenenergies for 2Δ = 3 meV (a, b) and 1.2 meV (c, d). The color bar is saturated above 0.9 meV. The white crosses in (a) show the EP coordinates limiting the blue area corresponding to real Fermi arcs. e–h same as (a–d), but for imaginary part. The color bar is saturated above 90 μeV. Imaginary Fermi arcs appear in blue. i, k Experimental and (j, l) theoretical phase (argument) of the difference of complex energies. EPs are associated to a vortex phase with a phase shift ± π whose winding is shown by the arrows in (i). m Length of the Fermi arc with respect to non-Hermiticity. Black, red points–experiments with sample 1,2 respectively (see Methods), blue line–theory. The maximal length of each Fermi arc (90∘) is marked with a thin red line. Error bars indicate the measurement uncertainty. The experimental points are obtained by varying the non-Hermiticity degree χ (controlled by the detuning Δ via applied voltage V).
