Spontaneous symmetry breaking in plasmon lattice lasers

We show spontaneous symmetry breaking (SSB) in a nonlocal metasurface laser. The system is a hexagonal plasmonic distributed feedback laser that lases at the six K-points in momentum space, or more exactly at the K and K’ modes. A unique properties is that these modes are exactly degenerate in both spatial distribution and energy. By simultaneous real-space and Fourier-space measurements, we map both the relative amplitude (parity symmetry breaking) and phase (rotational symmetry breaking ) of the two symmetry-broken modes. Our results open new perspectives on studying SSB and emergence of spatial coherence in photonic systems.