Mechanism of the Resistivity Switching Induced by Joule Heating in Crystalline NbO2

The memristive electrical transport properties in NbO2 are of great interest due to their promising application to neuromorphic computation. Much is still unknown about this material, in particular whether its metal-to-insulator transition (MIT) originates from the Peierls or the Mott mechanism. We use both measurement and first-principles calculation to develop a thermodynamic model of a second order Peierls MIT in NbO2 driven by Joule heating under bias voltage. The electrical conductivity is fit via temperature dependent energy gap, in accordance with weakening dimerization. The Joule heating equation is solved, and it is found that the system is unable to host a steady-state solution above a certain threshold bias. Finally, the Ginzburg-Landau theory is used to image the weakening of Nb-Nb dimers under heating. The resistivity switch can be understood by emergence of dimer-free conducting regions. Hence, we provide strong evidence of a domain wall model of NbO2 memristance.