Thin Films: Evidence for Critical Dynamics*

We investigate time-resolved dynamics in perovskite-type LaVO₃ thin film samples using femtosecond pump-probe spectroscopy. LaVO₃ is a Mott-Hubbard (MH) insulator that undergoes a magnetic transition at 143 K (paramagnetic to antiferromagnetic) and a structural phase transition at 141 K, below which orbital ordering occurs¹. Excitation of carriers across the MH gap with ~50 fs pulses initiates dynamics that manifest as changes in the reflectivity. In the vicinity of the magnetic transition, we observe dramatic slowing down in the recovery dynamics, consistent with critical-like dynamics at a 2^nd order phase transition², likely related to spin-ordering dynamics³. Further, we observe coherent acoustic phonons which also exhibit an anomalous response near ~140K.

¹S. Tomimito, et al, Physical Review B 68, 035106 (2003)
²R. V. Yusupov, et al, Physical Review B 81, 075103 (2010)
³D. M. Mazurenko, et al, Physical Review Letters 101, 245702 (2008)