Intrinsic insulating ground state in transition metal dichalcogenide TiSe2

The transition metal dichalcogenide TiSe2 has received significant research attention over the past four decades. Different studies have presented ways to suppress the 200 K charge-density-wave transition, vary lowerature resistivity by several orders of magnitude, and stabilize magnetism or superconductivity. Here we give the results of a synthesis technique whereby samples were grown in a high-pressure environment with up to 180 bar of argon gas. Above 100 K, properties are nearly unchanged from previous reports, but a distinct hysteretic resistance region begins around 80 K, accompanied by insulating lowerature behavior. Furthermore, an accompanying decrease in carrier concentration is seen in Hall effect measurements, and photoemission data show a removal of an electron pocket from the Fermi surface in an insulating sample. We conclude that high inert gas pressure synthesis accesses an underlying nonmetallic ground state in a material long speculated to be an excitonic insulator.