Resistive asymmetry in the metal-insulator transition of VO₂ and V₂O₃ nanowires

VO₂ and V₂O₃ are two examples of correlated oxides featuring a metal-insulator transition (MIT) at 340 K and 160 K, respectively. These transitions have attracted much attention, but few studies have addressed the effect of dimensional confinement.
We have studied the MIT in VO₂ and V₂O₃ nanowires as a function of their width. As it approaches to the characteristic domain size, a clear asymmetry develops in the R vs T curves: when cooling, the resistivity changes in few, large jumps; while it does it in a smooth way when warming.
Similar results have been observed in FeRh nanowires [1] and VO₂ nanobeams [2], suggesting that this might be a universal feature of first order phase transitions in 1D systems. However, different mechanisms were invoked to explain this phenomenon, and a universal explanation is still lacking. We show that this effect can be understood simply by considering the transition hysteresis together with the temperature dependence of the gap.
[1] V. Uhlír et al. Nat. Commun. 7, 13113 (2016).
[2] W. Fan et al. Phys. Rev. B 83, 235102 (2011).