Novel Phase Transitions in Layered Metal Chalcogenides: From Bulk to Atomically Thin Crystals

by Prof. Jun Sung Kim (POSTECH, 포항공과대학교)

Thursday May 10, 2018, 2:30 PM → 3:30 PM Asia/Seoul

206호 (제1과학관)

Atomically-thin crystals, recently realized using van der Waals materials, provide a versatile platform for studying the stability and tunability of the correlated electron phases in reduced dimension, as exemplified by various transition metal dichalcogenides (TMDs) hosting the charge-density-wave (CDW) phase. Here, we present the thickness dependence of the phase transition in the layered ternary metal chalcogenides, Ta2NiSe5, and Fe3GeTe2. ForTa2NiSe5, the excitonic insulating (EI) phase involving spontaneous condensation of electron and hole pairs is found to be stable down to a 2.5 unit-cell thickness without significant change of the transition temperature, in strong contrast to the CDW phases found in other TMDs. For Fe3GeTe2, the Ising type ferromagnetic ground state also remains stable even in 5 unit-cell thick crystals. The underlying mechanism of the phase stability of these two systems in the reduced dimension will be discussed.