Fig. 1: Difference between previously considered EP annihilation and this work.
From: Annihilation of exceptional points from different Dirac valleys in a 2D photonic system
a Typical EP annihilation where only a single Dirac valley is involved. EPs are created from a DP when increasing the relative non-Hermiticity χ. Conversely, they merge and form a DP when the relative non-Hermiticity decreases. b Annihilation of EPs described in this work, involving different valleys. 4 EPs are created from 2 DPs when increasing the relative non-Hermiticity. When it is increased further, the EPs meet and annihilate, leaving the system without any singularity. w is here the winding number.
