Tuning of the Electronic and Vibrational Properties of Transition Metal Selenides TSe 2 (T = Os, Ru) and Their Metallization at High Pressures

We present a systematic analysis of electrical properties of two transition metal selenides OsSe 2 and RuSe 2 under conditions of low temperature down to 1.8 K and external pressure up to 43 GPa. Both compounds have a pyrite-type crystal structure under ambient conditions and, according to Raman spectroscopy, do not undergo phase transitions up to the highest pressures. OsSe 2 and RuSe 2 undergo semiconductor-to-metal transitions at pressures up to 15 GPa. Further increase in pressure leads to the appearance of a superconducting transition at low temperatures. At 40 GPa, the critical temperatures of the superconducting transition reach maximum values of 5.5 and 6 K for RuSe 2 and OsSe 2 , respectively.