Correlation between crystal purity and the charge density wave in 1T-VSe2

We examine the charge density wave (CDW) properties of $1T\ensuremath{-}{\mathrm{VSe}}_{2}$ crystals grown by chemical vapor transport (CVT) under varying conditions. Specifically, we find that upon lowering the growth temperature (${T}_{g}l{630}^{\phantom{\rule{0.16em}{0ex}}\ensuremath{\circ}}\mathrm{C}$), there is a significant increase in both the CDW transition temperature and the residual resistance ratio (RRR) obtained from electrical transport measurements. Using x-ray photoelectron spectroscopy, we correlate the observed CDW properties with stoichiometry and the nature of defects. In addition, we have optimized a method to grow ultrahigh-purity $1T\ensuremath{-}{\mathrm{VSe}}_{2}$ crystals with a CDW transition temperature ${T}_{\mathrm{CDW}}=(112.7\ifmmode\pm\else\textpm\fi{}0.8)$ K and maximum residual resistance ratio $\mathrm{RRR}\ensuremath{\approx}49$, which is the highest reported thus far. This work highlights the sensitivity of the CDW in $1T\ensuremath{-}{\mathrm{VSe}}_{2}$ to defects and overall stoichiometry and the importance of controlling the crystal growth conditions of strongly correlated transition metal dichalcogenides.