Terahertz conductivity across the insulator-metal transition of epitaxial Praseodymium Nickel Oxide thin films

Here we report the low energy (0.8-7 meV) charge dynamics probed by Terahertz time domain transmission spectroscopy on 40 nm thick PrNiO₃ (PNO) thin films deposited on the (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 (LSAT) (110) substrate grown by pulsed laser deposition method. We have experimentally investigated both complex dielectric constant and optical conductivity spectra with respect to temperature ranging from 5 K to 300 K. Terahertz optical conductivity for PNO thin films shows two I-M transitions at 130 K (similar to that of the bulk PNO) and a re-entrant I-M transition around 25 K. The behavior of reentrant I-M transition at 25 K may be due to the presence of Pr₂NiO₄ minor impurity phase.