Substrate-dependent temperature-power scaling in V4O7 thin films across the metal–insulator transition

We investigate Joule-heating effects in thin films of the correlated oxide V4O7 across its metal–insulator transition (MIT) and associated electronic ordering regime, focusing on how substrate-dependent thermal boundary conditions affect nonequilibrium transport. By analyzing nonlinear current–voltage characteristics over a wide temperature range, we extract the temperature rise ΔT induced by Joule heating and find that ΔT follows a power-law dependence on dissipated channel power, ΔT∝Pβ. In the SiO2-grown V4O7 film, the scaling exponent β exhibits two distinct regimes: a low-temperature regime with β ≈ 0.4 below ∼140 K (within the measured range), and a high-temperature regime with β ≈ 1 above ∼240 K, corresponding to temperatures above the MIT. These regimes are reproducible across different current-sweep directions, indicating that the scaling behavior is intrinsic rather than an artifact of fitting or device inhomogeneity. In contrast, the V4O7 film grown on an Al2O3 (r-cut) substrate—prepared in the same growth run and under identical deposition conditions as the SiO2-grown film—exhibits purely Ohmic transport at representative temperatures over the explored bias range, indicating that more efficient heat dissipation in this sample plays an important role in suppressing access to nonlinear electrothermal scaling under the present measurement conditions. The absence of sharp features in the equilibrium resistivity across the low-temperature region where β changes suggests that the observed crossovers are associated with bias-driven thermal response rather than changes in the underlying electronic phase. Our results highlight substrate-dependent electrothermal scaling as an important factor in nonequilibrium transport in V4O7 thin films across the MIT and provide a framework for interpreting Joule-heating-induced transport behavior under different thermal boundary conditions.