Parity breakdown, vortices, and dark soliton states in a Bose gas of resonantly excited polaritons.

A new mechanism of parity breakdown in a spinor Bose gas is predicted; it causes a single-mode state of polaritons to be spontaneously divided into different polarization domains which annihilate each other at the interface areas. In a polariton wire, such interface is a dark soliton that can run in space without dissipation. In a planar cavity, quantized vortices arise in which phase difference of orthogonally polarized components makes one complete turn around the core. Coupled vortex-antivortex pairs and straight filaments can form in analogy to Bose-Einstein condensates and superconductors. However, the rotational symmetry is broken even for individual vortices, which makes them interact on a large scale and form internally ordered structures. These states come into being under resonant excitation if the spin coupling rate significantly exceeds the decay rate.