Isao Inoue: Electrostatic control of insulating SrTiO3 surface: insulator-metal transition, negative capacitance, multi- band conduction, Kondo effect, and more
|When:||Mo 29-08-2016 10:00 - 11:00|
In this talk, we demonstrate that a quite insulating ‘non - doped’ SrTiO 3 shows a two-dimensional (2D) insulator-metal transition at thesurface by applyingan electric field and it actually works as an excellent FET with sufficiently good sub- threshold swing ( ∼ 170 mV/decade) and very large carrier mobility ( ∼ 10 cm2/Vs). SrTiO 3 is well known for its defect-prone surface, but by inserting a thin (6 nm) organic insulator Parylene-C between the surface and the high-k gate insulator HfO 2 , we can avoid any damages on the surface during the de- vice fabrication as well as during the application of the gate voltage.This clean interface between Parylene-C and SrTiO 3 is not only promisingfor the electronic application of the SrTiO 3 -FET but also unexpected intriguing electronic properties of the SrTiO 3 surface are getting revealed oneafter another.
This clean interface between Parylene-C and SrTiO 3 is not only promisingfor the application of the SrTiO 3 -FET but also unexpected intriguing electronic properties of the SrTiO 3 surface are get- ting revealed one after another.We can accumulate 2D carriers more than 10 14 cm 2 , which is surprisingly beyond the value expected from the capacitance of the gate insulator (the phenomenon is called “negative capacitance” )  . By increasing the gate voltage V G , the channel resistance decreases, and the temperature dependence exhibits a clear insulatorto metal transition with the boundary at the quantum resistance. Metallic channel shows the Kondo effect at low temperatures, as well as an anomaly of the Hall effect withouthysteresis is accompanied. All these resultssuggest consistently the lifting of the three-fold degenerate t 2g band, which is most probablycaused by a strong Rashbaeffect at the surface. We will explain these phenomena with the experimental data, and discuss on the rich physics behind them.