title: Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2.
abstract: A(1-x)Fe(2-y)Se2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are antiferromagnetic (AFM) insulating phases, and they have extremely high Néel transition temperatures. However, control of carrier doping into the parent AFM insulators has been difficult due to their intrinsic phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2 insulating epitaxial film with an atomically flat surface and examined its electrostatic carrier doping using an electric double-layer transistor (EDLT) structure with an ionic liquid gate. The positive gate voltage gave a conductance modulation of three orders of magnitude at 25 K, and further induced and manipulated a phase transition; i.e., delocalized carrier generation by electrostatic doping is the origin of the phase transition. This is the first demonstration, to the authors' knowledge, of an EDLT using a Mott insulator iron selenide channel and opens a way to explore high Tc superconductivity in iron-based layered materials, where carrier doping by conventional chemical means is difficult.
authors.affiliation: Frontier Research Center, Materials and Structures Laboratory, and Materials Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Katase
authors.forename: Hidenori
authors.initials: H
authors.lastname: Hiramatsu
authors.forename: Toshio
authors.initials: T
authors.lastname: Kamiya
authors.forename: Hideo
authors.initials: H
authors.lastname: Hosono
mesh_terms: D058085:Iron Compounds / Q000737:chemistry*; D008956:Models, Chemical; D012643:Selenium / Q000737:chemistry*; D055672:Static Electricity; D013696:Temperature; D014173:Transistors, Electronic
chemical_list: D058085:Iron Compounds; D012643:Selenium
keywords: Fe-based superconductors; field-effect devices