Predicted photoinduced pair annihilation of emergent magnetic charges in the organic salt $\alpha$-(BEDT-TTF)$_2$I$_3$ irradiated by linearly polarized light

TL;DR

This paper predicts that linearly polarized light can induce pair annihilation of magnetic charge analogs in a specific organic conductor, leading to a non-topological phase transition, offering a potential experimental observation of magnetic monopole-like phenomena.

Contribution

It introduces a theoretical prediction of photoinduced pair annihilation of magnetic charge analogs in a real material using Floquet theory, distinct from topological phase transitions.

Findings

Pair annihilation occurs under linearly polarized light irradiation.

The transition is to a Floquet normal insulator phase, not a topological phase.

The material's band structure enables experimental observation of this phenomenon.

Abstract

Prolonged experimental attempts to find magnetic monopoles (i.e., elementary particles with an isolated magnetic charge in three dimensions) have not yet been successful despite intensive efforts made since Dirac's proposal in 1931. Particle physicists have predicted the possible collision and pair annihilation of two magnetic charges with opposite signs. However, if such annihilation exists, its experimental observation would be difficult because its energy scale is predicted to be tremendously high ($\sim$10$^{16}$ GeV). In the present work, we theoretically predict using the Floquet theory that a pair of slightly gapped Dirac-cone bands in a weakly-charge-ordered organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$, which behave as magnetic charges with opposite signs in the momentum space, exhibit pair annihilation under irradiation with linearly polarized light. This photoinduced pair annihilation is accompanied by a non-topological phase transition to the Floquet normal insulator phase in contrast to the well-known circularly-polarized-light-induced topological phase transition to the Floquet Chern insulator phase. We discuss that $\alpha$-(BEDT-TTF)$_2$I$_3$ has a peculiar band structure capable of realizing a suitable experimental condition (i.e., off-resonant condition) and a charge ordered state providing a required staggered site potential and thereby provides a rare example of materials that can be used to observe the predicted pair annihilation phenomenon. The feasibility of experimental observation is also discussed.