Unconventional magnetism mediated by spin-phonon-photon coupling

TL;DR

This paper theoretically predicts a novel form of long-range, biquadratic spin interaction mediated by hybridized spin-phonon-photon states, leading to unconventional magnetic order with potential applications in low-power magnetic memories.

Contribution

It introduces a new mechanism for magnetic ordering via virtual polariton exchange, distinct from traditional exchange interactions, and highlights its unconventional properties.

Findings

Long-range biquadratic spin interaction mediated by polaritons.

First-order phase transition to magnetic order with abrupt magnetization.

Potential for ultralow-power, thermally-assisted magnetic memory applications.

Abstract

Magnetic order typically emerges due to the short-range exchange interaction between the constituent electronic spins. Recent discoveries have found a crucial role for spin-phonon coupling in various phenomena from optical ultrafast magnetization switching to dynamical control of the magnetic state. Here, we demonstrate theoretically the emergence of a biquadratic long-range interaction between spins mediated by their coupling to phonons hybridized with vacuum photons into polaritons. The resulting ordered state enabled by the exchange of virtual polaritons between spins is reminiscent of superconductivity mediated by the exchange of virtual phonons. The biquadratic nature of the spin-spin interaction promotes ordering without favoring ferro- or antiferromagnetism. It further makes the phase transition to magnetic order a first-order transition, unlike in conventional magnets. Consequently, a large magnetization develops abruptly on lowering the temperature which \aknew{could} enable magnetic memories admitting ultralow-power thermally-assisted writing while maintaining a high data stability. The role of photons in the phenomenon further enables an in-situ static control over the magnetism. These unique features make our predicted spin-spin interaction and magnetism highly unconventional paving the way for novel scientific and technological opportunities.