Selective excitation of vibrational modes using strong laser pulses has emerged as a powerful material engineering paradigm. However, to realize deterministic control over material properties for device applications, it is desirable to have an analogous scheme without a drive, operating in thermal equilibrium. We here propose such an equilibrium analog of the light-driven paradigm, leveraging the strong coupling between lattice degrees of freedom and the quantum fluctuations of the electric field of a THz micro-cavity. We demonstrate this approach by showing, using ab initio data, how electric field fluctuations can induce a sub-dominant ferromagnetic order, on top of the dominant zig-zag antiferromagnet order, in FePS3 close to its N\'eel temperature.
@article{arxiv.2409.19063,
title = {Equilibrium non-linear phononics by electric field fluctuations of terahertz cavities},
author = {Emil Viñas Boström and Marios H. Michael and Christian Eckhardt and Angel Rubio},
journal= {arXiv preprint arXiv:2409.19063},
year = {2025}
}