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

Lucy S. Nathwani, Anne Ruperto+9 more|arXiv (Cornell University)|Mar 22, 2026

Thermal properties of materials0 citations

TL;DR

The study uses frequency-domain thermoreflectance and photoreflectance on a 57.5 nm NdNiO3 thin film to reveal domain-mediated, anisotropic transport across the metal–insulator transition, with reduced out-of-plane hysteresis compared to in-plane behavior and a distinct ambipolar diffusivity change.

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.

Motivation & Objective

• Motivate the use of thin-film NdNiO3 as a tunable platform for temperature-driven metal–insulator transitions in electronics.
• Investigate cross-plane (out-of-plane) thermal transport across MIT in an epitaxial NdNiO3 film.
• Probe ambipolar carrier diffusion across MIT using FDPR to link electronic and thermal transport.
• Understand how nanoscale domain structure and film thickness influence macroscopic transport hysteresis.

Proposed method

• Use frequency-domain thermoreflectance (FDTR) with a gold transducer to measure the out-of-plane thermal conductivity κ⊥ of a 57.5 nm NdNiO3 film on LaAlO3.
• Use frequency-domain photoreflectance (FDPR) on an adjacent bare region to extract ambipolar diffusivity Da across the MIT.
• Fit FDTR data with a Fourier heat conduction model to extract κ⊥ and thermal boundary conductance GFS; fix substrate properties from independent FDTR measurements on LaAlO3.
• Model FDPR signals as a carrier-plus-thermal diffusion problem; fix carrier amplitude Aρ and recombination time τ to robustly extract Da and GFS.
• Fix film heat capacity using a Debye model derived from NdNiO3 bulk data to stabilize κ⊥ fits.
• Compare cooling and heating cycles to assess hysteresis and identify Tswitch from thermal and electronic proxies.

Figure 1: (a) Distorted perovskite structure of NdNiO 3 in the insulating phase. (b) The structure in the metallic phase. The changes in octahedral tilts drive the transition 8 . (c) Temperature-dependent resistance capturing the MIT (see SI). $T_{\mathrm{MIT}}$ is 91 K during cooling and 124 K duri

Experimental results

Research questions

• RQ1 What is the out-of-plane thermal conductivity behavior of NdNiO3 across its MIT in thin-film form?
• RQ2 How does ambipolar diffusivity evolve across the MIT, and how is it coupled to thermal transport?
• RQ3 To what extent does thin-film geometry and domain size influence hysteresis and percolation in cross-plane transport?
• RQ4 Can FDTR and FDPR together resolve nanoscale domain dynamics during the MIT in NdNiO3?

Key findings

• Out-of-plane thermal conductivity κ⊥ of NdNiO3 shows a 33% decrease between 123.3 K and 110.0 K during cooling (thermal switching).
• The heating and cooling curves for κ⊥ show weak hysteresis, indicating anisotropic transport relative to in-plane measurements.
• Ambipolar diffusivity Da measured by FDPR decreases sharply from 120 K to 110 K across the MIT, with weaker hysteresis than electrical transport.
• The switch temperature Tswitch is determined to be 115 ± 4 K from FDTR/FDPR fits.
• The film’s thickness (~57.5 nm) is comparable to the inferred domain length scales (100–300 nm laterally; domains bridging percolation out-of-plane), explaining reduced out-of-plane hysteresis due to limited vertical percolation.
• A thinner 20.6 nm NdNiO3 film shows similar lack of out-of-plane hysteresis, indicating the effect is robust to modest thickness variation.

Figure 2: (a) Schematic of an integrated frequency-domain thermoreflectance (FDTR) and frequency-domain photoreflectance (FDPR) measurement setup. A continuous wave (CW) pump laser at 458 nm, power-modulated at a frequency $\omega/2\pi$ , excites the sample. A CW probe laser at 532 nm reads out the