Observation of microscopic domain effects in the metal-insulator transition of thin-film NdNiO$_3$

TL;DR

This study uses advanced optical techniques to reveal how microscopic domain effects influence the metal-insulator transition in NdNiO$_3$ thin films, showing sharp changes in thermal and charge transport properties.

Contribution

It demonstrates the application of FDTR and FDPR techniques to probe microscopic domain effects in NdNiO$_3$, revealing anisotropic transport behavior across the transition.

Findings

Sharp change in out-of-plane thermal conductivity at transition

Large change in ambipolar diffusivity of photoexcited carriers

Negligible hysteresis in out-of-plane transport despite electrical resistance hysteresis

Abstract

Perovskite oxides display correlated electrical, magnetic, and thermal properties that can be further tuned in the thin-film limit, making them contenders for next-generation electronics. Measuring thermal transport in thin films is challenging, because traditional techniques are dominated by the substrate. Here, frequency-domain thermoreflectance (FDTR) of an epitaxial NdNiO$_3$ thin film reveals a sharp change in out-of-plane thermal conductivity across the metal-insulator transition. Complementary frequency-domain photoreflectance (FDPR) reveals a large change in ambipolar diffusivity of photoexcited carriers. While the in-plane electrical resistance shows large hysteresis, out-of-plane thermal and charge transport shows negligible hysteresis. We attribute this discrepancy to anisotropy in the percolation of nanoscale domains across the transition as the film thickness approaches the domain length scale. We establish FDTR and FDPR as sensitive probes of quantum material phase transitions and highlight NdNiO$_3$ for thermal control and memory applications.