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

We examine the charge density wave (CDW) properties of 1T-VSe2 crystals grown by chemical vapor transport (CVT) under varying conditions. Specifically, we find that upon lowering the growth temperature (Tg<630°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-VSe2 crystals with a CDW transition temperature TCDW=(112.7±0.8) K and maximum residual resistance ratio RRR≈49, which is the highest reported thus far. This work highlights the sensitivity of the CDW in 1T-VSe2 to defects and overall stoichiometry and the importance of controlling the crystal growth conditions of strongly correlated transition metal dichalcogenides.