Abstract
Many strongly correlated transition metal oxides exhibit a metal-insulator transition (MIT), the manipulation of which is essential for their application as active device elements. However, such manipulation is hindered by lack of microscopic understanding of mechanisms involved in these transitions. A prototypical example is VO2, where previous studies indicated that the MIT resistance change correlate with changes in carrier density and mobility. We studied the MIT using Hall measurements with unprecedented resolution and accuracy, simultaneously with resistance measurements. Contrast to prior reports, we find that the MIT is not correlated with a change in mobility, but rather, is a macroscopic manifestation of the spatial phase separation which accompanies the MIT. Our results demonstrate that, surprisingly, properties of the nano-scale spatially-separated metallic and semiconducting domains actually retain their bulk properties. This study highlights the importance of taking into account local fluctuations and correlations when interpreting transport measurements in highly correlated systems.
Highlights
Are the need to stabilize temperature for each measurement to decrease noise, while avoiding overshoot of the set temperature which will introduce errors through hysteresis effects and need of large magnetic field sweeps to increase accuracy
In contrary to previous reports, the resistance behaviour does not correspond to the changes in the Hall coefficient
The films were patterned via reactive ion etching (RIE) into one of two commonly recommended geometries for Hall measurements[39]: a disc with diameter of 900 μ m, or a 4-leaf clover with identical outer diameter and inner spacing of 290 μ m
Summary
Are the need to stabilize temperature for each measurement to decrease noise, while avoiding overshoot of the set temperature which will introduce errors through hysteresis effects and need of large magnetic field sweeps to increase accuracy. All these make the measurement extremely time-consuming. We measure the Hall coefficient on single-phase thin VO2 films, simultaneously with the resistance, across the temperature driven MIT. We analyse the results in the context of spatial inhomogeneity of metallic and semiconducting domains during the transition, by introducing the exact relation theorem and effective medium approximation[36,37,38]. At close vicinity to the percolation threshold we do observe a difference between the experimental results and the exact relation predictions, and discuss possible origins
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