Electrodynamics near the metal-to-insulator transition in ${\mathrm{V}}_3{\mathrm{O}}_5$

The electrodynamics near the metal-to-insulator transitions induced, in ${\mathrm{V}}_3{\mathrm{O}}_5$ single crystals, by both temperature $\left(T\right)$ and pressure $\left(P\right)$ has been studied by infrared spectroscopy. The $T$ and $P$ dependence of the optical conductivity may be explained within a polaronic scenario. The insulating phase at ambient $T$ and $P$ corresponds to strongly localized small polarons. Meanwhile the $T$-induced metallic phase at ambient pressure is related to a liquid of polarons showing incoherent dc transport, in the $P$-induced metallic phase at room $T$ strongly localized polarons coexist with partially delocalized ones. The electronic spectral weight is almost recovered, in both the $T$- and $P$-induced metallization processes, on an energy scale of $1\mathrm{eV}$, thus supporting the key role of electron-lattice interaction in the ${\mathrm{V}}_3{\mathrm{O}}_5$ metal-to-insulator transitions.

Figure 1

(Color online) $\left(P\text{−}T\right)$ Pictorial phase diagram of ${\mathrm{V}}_3{\mathrm{O}}_5$ as determined in Ref. 7. The AF order is found at ambient pressure below $T_N=75\mathrm{K}$. The thick curve represents the $P$ dependence of $T_N$ (Ref. 8). The measurements performed in this paper vs both $T$ and $P$ have been collected over the black markers shown in figure.

Figure 2

(Color online) Full-scale temperature dependence of $R\left(\omega \right)$, and its far-infrared behavior (inset).

Figure 3

(Color online) Real part of the optical conductivity ${\sigma }_1\left(\omega \right)$ at various temperatures. Diamonds are ${\sigma }_{\mathrm{dc}}$ data from resistivity measurements of Ref. 10. In the inset the MIR peak frequency $\left({\omega }_{\mathrm{MIR}}\right)$ and its half-width at half-maximum $\left({\Gamma }_{\mathrm{MIR}}\right)$, as a function of temperature are shown. Those values have been obtained by a Drude-Lorenz fit of the optical conductivity (see text).

Figure 4

(Color online) Spectral weight as a function of frequency at given temperatures. In the inset both the $T$ dependence of the phonon-subtracted SW at $800{\mathrm{cm}}^{-1}$ and the dc conductivity (from Ref. 10) are shown.

Figure 5

(Color online) Upper panel: reflectivity curves measured at the sample-diamond interface are shown at room $T$ for selected pressures and compared to the ambient pressure (black line) sample-diamond reflectivity (see text). Thin continuous lines are fitting curves obtained by a Drude-Lorentz model (see text): only two of them are shown for clarity. In the inset, the quantity $\Delta R∕R$ is shown at $1600{\mathrm{cm}}^{-1}$. The dashed line is a phenomenological sigmoid fit to data. Lower panel: Optical conductivity curves obtained by the fitting parameters, compared with the ambient $P\text{−}T$ conductivity. Diamond symbols are ${\sigma }_{\mathrm{dc}}$ data from resistivity measurements of Ref. 7. Thin dashed lines are the HF- and the LF-MIR components of the fit for $P=9.8\mathrm{GPa}$ data. In the inset both the total spectral weight and that of the MIR components is shown.