Femtosecond modulation of electron correlations in a Luttinger liquid

Luttinger liquids emerge in one-dimensional metals with strong electron interactions, exhibiting intriguing near-equilibrium properties such as spin-charge separation and power-law correlations. Although these interactions suggest fast, distinctive out-of-equilibrium dynamics, such phenomena remain largely unexplored on ultrashort timescales. Here, we use femtosecond laser excitation to weakly deplete the electron density in the Luttinger band of Li_0.9Mo₆O₁₇ and track the response via time- and angle-resolved photoemission spectroscopy. By fitting the measured electron distributions to a finite-temperature Luttinger liquid model, we observe a fast drop in the Luttinger exponent, quantifying the strength of electron interactions. Subsequently, unlike hot electrons in conventional Fermi liquids that slowly relax within picoseconds via electron-phonon coupling, hot electrons in Li_0.9Mo₆O₁₇ relax within a short time of ~100 femtoseconds, through the excitation of a nonequilibrium collective plasmon. The extremely fast evolution of the Luttinger exponent and electron temperature-including a tens of femtosecond time lag between excitation, recovery, and plasmon-driven modulation-reveals previously unidentified pathways for modulating quantum many-body interactions in low-dimensional materials.