Jian-ting Ye: Liquid-gated interface superconductivity on an atomically flat film

Jian-ting Ye discussed their recent beautiful work from Tokyo on gating various materials to induce superconductivity (and other states of matter) using ionic and organic electrolyte solutions. They make an electronic double layer transistor (EDLT) with liquid gating. Much more charge is introduced as compared to conventional SiO2 style dielectrics.

Jiang-ting discussed a large number of results using this technique. With polymer electrolyte solutions, they have found a 2D metal-insulator transition in ZnO. (As a practical matter, states induced by this method will generally be 2D) For smooth changes of voltage, there is a sudden onset in resistance when resistance gets near h/e^2. They have also induced superconductivity in StTiO3 around 0.4K, which is a similar temperature to that found recently in STO/LaAlO3 superlattices. Capacitance is high enough that for materials like graphene they can see particular bands crossing the Fermi level in the case of graphene.

To get larger charge densities they use ionic liquids where they get get ~ 20 times higher charge density than with polymer electrolytes. They have looked at many layered structures (cuprate superconductors, layered chalcogenide topological insulators, layered chalcogenide superconductors, etc.) and found a number of effects. But in the rest of talk will talk he was going to emphasize their work on superconductors.

ZrNCl was induced to be a superconductor at 15.2K with Tc's very similar to what is found when this material is doped with Li.

Transition metal chalcogenide MoS2 when electron doped with the EDLT technique is found to have superconductivity at 9K. This is higher than the previous record of about 6.5K when this system is doped with alkali metals. They also find ambipolar conductivity for positive and negative bias in this system, but no ambipolar superconductivity yet.

It was asked by Finkelstein why it is that there is is no problem with mobility in these systems, in the sense that in 2D electron glass in semiconductor heterostructures, dopant layers reduce mobilities. Why does not this not happen here? The speaker replied that they are in a different regime with regard to the range of mobilities. Here mobilities are in the 100's at best, whereas the best 2DEG have mobilities 10^4.

Blogged by N. Peter Armitage