Photoinduced Frustration Modulation in $\kappa$-type Quantum Spin Liquid Candidates

TL;DR

This study demonstrates that midinfrared pulses can coherently excite molecular vibrations in quantum spin liquid candidates, enabling dynamic control of geometric frustration and electronic properties in these complex materials.

Contribution

It introduces a novel method of using ultrafast midinfrared pulses to modulate frustration in quantum spin liquids via vibrational coupling.

Findings

Nonlinear coupling between molecular vibrations and phonons observed.

Ultrafast reflectivity measurements reveal electronic response modulation.

Dynamic control of frustration demonstrated in organic quantum materials.

Abstract

Geometric frustration is a key parameter controlling electronic and magnetic properties of quantum spin liquid systems, yet remains challenging to tune. Here, we coherently drive molecular vibrations with midinfrared pulses in two organic quantum spin liquid candidates, the insulating $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ and the metallic $\kappa$-(BEDT-TTF)$_4$Hg$_{2.89}$Br$_8$, and probe their electronic response through ultrafast reflectivity measurements. We observe a nonlinear coupling between local molecular vibrations and nonlocal phonons, which is expected to directly modulate the geometric frustration of their triangular lattice. Our findings establish a promising route to dynamically control frustration in nonbipartite quantum materials.