Tuning low temperature electrical resistivity in TiSe₂

TiSe₂ has been one of the most studied and debated transition metal dichalcogenides in part due to an indirect band gap/overlap that is difficult to resolve. It has been known for some time that dilute impurities and growth conditions can drastically affect the transport properties of TiSe₂. Much attention has been paid to the anomalous feature in temperature dependent resistivity near 150 K where a charge-density-wave transition forms, but there has been little reported on the low temperature resistivity, where there is large discrepancy between polycrystalline and single crystalline samples. We confirm the metallicity in single crystalline TiSe₂ grown by the chemical vapor transport method is caused by dilute iodine as a transport agent during growth, which gives rise to formation of impurity bands near the Fermi surface. On the other hand, the polycrystalline sample synthesized by solid state reaction without extrinsic additives shows intrinsically insulating ground state of TiSe₂. Furthermore, we demonstrate the ability to tune the insulating behavior of TiSe₂ with different synthesis parameters.