Spin-orbit entangled excitons (SOEEs) in two-dimensional (2D) antiferromagnets provide direct access to explore unconventional many-body interactions in correlated electron systems. In this work, we carry out a detailed investigation using nondegenerate isotropic and anisotropic pump-probe reflection spectroscopy to probe the ultrafast dynamics of SOEEs and their coupling to spin fluctuations in ${\mathrm{NiPS}}_3$. Transient reflectivity data reveal acoustic phonon oscillations at $\sim 27\mathrm{GHz}$, along with two distinct relaxation timescales: fast (1–9 ps) and slower components (1–4 ns) associated with SOEE coherence and spin reordering, respectively. Both timescales exhibit pronounced temperature dependence near the exciton dissociation ($T_{\mathrm{ED}}=120\text{K}$) and Néel ($T_{\mathrm{N}}=155\text{K}$) temperatures. The SOEE coherence shortens from $\sim 9$ ps at $T<T_{\mathrm{ED}}$ to $\sim 3$ ps at $T>T_{\mathrm{ED}}$ with a finite tail persisting beyond $T_{\mathrm{N}}$. The spin reordering time grows near 120 K, and shows a critical slowing down around $T_{\mathrm{N}}$. Pump fluence studies further corroborate their spin origin. Our findings uncover the direct interplay between the excitonic and spin degrees of freedom across ultrafast and longer timescales, offering distinct opportunities to probe and engineer emergent many-body interactions in 2D antiferromagnets.

Close

PrevNext

View figure in article

• Carrier dynamics
• Excitons
• Kerr effect
• Magnetic order
• Magnetic phase transitions
• Spin dynamics
• Spin-orbit coupling
• Ultrafast magnetic effects