Exciton multipolarity controls coherent and squeezed phonons in van der Waals heterostructures
Year: 2026
Type: preprint
Abstract: Photoexcitation-driven changes in the electronic distribution displace atoms, generating coherent phonons on ultrafast timescales. Two-dimensional (2D) materials and their heterostructures offer a powerful platform for engineering these phonons. Yet, despite the widespread observation of photoexcited coherent phonons, a design principle for controlling their character remains elusive. Here, using detailed atomistic simulations of multilayers of alternating MoSe$_2$ and WSe$_2$, we reveal exciton multipolarity as a design principle for tuning photoinduced phonons from coherent to squeezed. These phonons are interlayer breathing modes, with dipolar excitons coupling linearly to generate coherent states and quadrupolar excitons coupling quadratically to produce squeezed states. Moreover, an out-of-plane electric field enables switch-like control, converting quadrupolar excitons into dipolar excitons and switching the phonon state from squeezed to coherent. For example, in trilayer WSe$_2$/MoSe$_2$/WSe$_2$, the photoexcited 1.04-THz breathing mode switches from a squeezed state at zero field to a coherent state under an applied vertical field. Experimentally, these phonon states can be directly probed by ultrafast X-ray or electron diffraction and indirectly through transient reflectivity. Our results open new avenues for ultrafast control of lattice and electronic dynamics on picosecond timescales, with implications for THz quantum phononics, nanophotonic technologies, and quantum-noise-limited sensing.
Source: arXiv (Cornell University)
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7208727185