Spontaneous spin bifurcations and ferromagnetic phase transitions in a spinor exciton-polariton condensate

TL;DR

This paper reports the observation of spontaneous spin bifurcations and ferromagnetic phase transitions in a spinor exciton-polariton condensate, revealing how the system spontaneously magnetizes and can be optically controlled.

Contribution

It demonstrates the first experimental observation of spontaneous parity breaking and ferromagnetic phase transition in a spinor exciton-polariton condensate with optical control capabilities.

Findings

Condensate spontaneously magnetizes at a critical density.

Magnetization states can be optically inverted with weak pulses.

Stable ferromagnetic states persist for seconds at low temperature.

Abstract

We observe a spontaneous parity breaking bifurcation to a ferromagnetic state in a spatially trapped exciton-polariton condensate. At a critical bifurcation density under nonresonant excitation, the whole condensate spontaneously magnetizes and randomly adopts one of two elliptically polarized (up to 95% circularly-polarized) states with opposite handedness of polarization. The magnetized condensate remains stable for many seconds at 5 K, but at higher temperatures it can flip from one magnetic orientation to another. We optically address these states and demonstrate the inversion of the magnetic state by resonantly injecting 100-fold weaker pulses of opposite spin. Theoretically, these phenomena can be well described as spontaneous symmetry breaking of the spin degree of freedom induced by different loss rates of the linear polarizations.