Dirac magnons pairing via pumping

TL;DR

This paper investigates how electromagnetic pumping can induce pairing of Dirac magnons in honeycomb ferromagnets, leading to a new magnetic state with reduced or zero magnetization, potentially observable in CrBr3 or CrCl3 near their Curie temperatures.

Contribution

It introduces a bosonic analog of the Cooper ladder for magnon pairs, demonstrating enhanced pairing at Dirac points and predicting a novel paired magnetic state.

Findings

Magnon pairing at Dirac points enhances due to a bosonic Cooper-like mechanism.

The system becomes unstable towards a paired magnetic state with reduced magnetization.

Possible realization of the Dirac magnon paired state in CrBr3 or CrCl3 near Curie temperature.

Abstract

We study pumping of magnons to the Dirac points of magnon's Brillouin zone of a ferromagnet on a honeycomb lattice. In particular, we consider second-order Suhl process, when due to interaction between magnons, a pair of magnons is created due to absorption of two electromagnetic wave quanta. We introduce a bosonic analog of the Cooper ladder for the magnon pair, which is shown to enhance the pairing of magnons at the Dirac points. As a result of pairing of the Dirac magnons, the system becomes unstable towards formation of a magnetic state with zero or reduced magnetization - the Dirac magnon paired state. In this case the resonant frequency of the pump equals to that of energy of the Dirac points. Our estimates suggest that the Dirac magnon paired state can be found in the CrBr$_{3}$ or CrCl$_{3}$ ferromagnet below in vicinity of the Curie temperature.