Systematics in the metal-insulator transition temperatures in vanadium oxides

TL;DR

This paper reveals simple linear systematics in the metal-insulator transition temperatures of vanadium oxides, linking electron-electron and electron-phonon interactions across different compounds.

Contribution

It uncovers two universal linear relationships describing the difference in transition contributions for various vanadium oxides, simplifying understanding of their transition mechanisms.

Findings

Data points align on two straight lines in T_M - T_P versus 1/n plots.

Two distinct linear relationships are identified for different groups of vanadium oxides.

The systematics provide a unified framework for understanding transition temperatures.

Abstract

Nine of the known vanadium oxides, VO$_{2-1/n}$ (n - a positive or negative integer) with n=2 - 6, 8, 9, $\infty$ and -6, undergo metal-insulator transitions accompanied by structural transitions, at various temperatures T$_{MIT}$ (V$_7$O$_{13}$ is metallic above T=0). Among the persistent efforts to determine the driving force(s) of these transitions, electron-electron (Mott-like) and electron-phonon (Peierls-like) interactions, there were several attempts to find systematics in T$_{MIT}$ as function of n. Here we present an unexpectedly simple and illuminating systematics that holds for positive n: if T$_{MIT}$ is the absolute value of the difference between T$_M$(n) and T$_P$(n), which represent the contributions of electron-electron and electron-phonon interactions, respectively, all data points of T$_M$-T$_P$ versus 1/n lie on, or close to, two simple straight lines; one is T$_M$-T$_P$= T$_{\infty}$(7/n-1) for V$_3$O$_5$, V$_4$O$_7$, V$_5$O$_9$, V$_7$O$_{13}$, V$_8$O$_{15}$, V$_9$O$_{17}$ and VO$_2$ and the other is T$_M$-T$_P$= T$_{\infty}$(3/n-1) for V$_2$O$_3$, V$_6$O$_{11}$ and VO$_2$.