Evidence of metal-semimetal-transition from Cu2TlSe2 to Cu2TlTe2.

Transition metal compounds with quasi-two-dimensional structure demonstrate a series of un-precedent quantum phases, such as topological insulator, topological phase transition under thermal/pressure stimuli, which is attributed to delicate interplay among interlayer coupling, spin-orbit coupling and stoichiometry. Here, Cu 2 TlSe 2 and Cu 2 TlTe 2 crystals were successfully synthesized by Bridgeman method. Highly crystalline quality of these samples is verified by X-ray diffraction and microstructural characterization. Temperature-dependent-Hall-resistivity shows that Cu 2 TlSe 2 is hole-like and Hall resistivity is in-sensitive to temperature; while Hall resistivity of Cu 2 TlTe 2 is positive at room temperature and change to negative at 30 K. Combined experimental results and electronic band structures calculated by first-principles method, it is revealed that Cu 2 TlSe 2 is a metal, but Cu 2 TlTe 2 is a semi-metal. This work demonstrates the rich physical phases of layered transition metal compounds under the interplay among interlayer coupling, spin-orbit coupling and stoichiometry. [ABSTRACT FROM AUTHOR]