Hot Electron-Driven Structural Expansion and Magnetic Collapse in Bilayer FeSe

TL;DR

This study demonstrates that ultrafast laser excitation of bilayer FeSe induces simultaneous structural expansion and magnetic collapse, revealing a pathway to control quantum phases in iron-based materials.

Contribution

First-principles calculations show how hot electron excitation causes structural and magnetic phase transitions in bilayer FeSe, a novel control mechanism for quantum states.

Findings

Photoexcited hot electrons induce structural expansion in bilayer FeSe.

Magnetic order collapses under increased electronic excitation.

Ultrafast laser can tune quantum phases in FeSe thin films.

Abstract

Quantum phenomena emerging from the interaction of light and matter in low-dimensional systems hold great potential for future quantum technologies. Here, using first-principles calculations incorporating non-local van der Waals interactions and Hubbard corrections, we report simultaneous structural expansion and magnetic collapse in bilayer FeSe induced by photoexcited hot electrons. Our calculations reveal that, while bulk FeSe is paramagnetic, as observed experimentally, double-layer FeSe exhibits robust {\it staggered} antiferromagnetic order at low temperatures with a net site magnetization of $\sim 2.75~\mu_B$/Fe. However, increasing the density of photoexcited electrons systematically enhances the internal electronic entropy, leading to a complete collapse of antiferromagnetic order accompanied by an abrupt expansion of the interlayer separation. Our findings suggest the structural and magnetic properties of FeSe thin films can be finely tuned via ultrafast laser excitation, offering a pathway to control quantum phases in iron-based compounds through electronic temperature.