Colloquium：Novel Routes for exploring high-Tc superconductivity in FeSe-derived compounds (Xianhui Chen,Nov 18)

Colloquium

Title:  Novel Routes for exploring high-Tc superconductivity in FeSe-derived compounds

Speaker: Xianhui Chen, Professor, University of Science and Technology of China

Location: Room 111, Physics Building

Time: 15:00-16:00, Wed, Nov 18, 2015

Abstract:

In this talk, we report on our recent progress of novel routes for exploring high-Tc superconductors in FeSe-derived compounds. Firstly, we synthesized an air-stable material, (Li0.8Fe0.2)OHFeSe, which shows superconducting transition temperature up Tc to ~40 K, by means of a novel hydrothermal method. The crystal structure is unambiguously determined by a combination of X-ray and neutron powder diffraction and nuclear magnetic resonance. Moreover, antiferromagnetic order is found to coexist with superconductivity. Secondly, we realized high Tc with a maximum up to 43 K in single crystals of (Li,Fe)OHFeSe (with initial Tc~25 K), by liquid-ionic gating technique in the thin flakes of single crystal, and observed a striking first-order transition from superconductor to AFM insulator on the strong charge doping region, just at the verge of optimal doping with highest Tc. We also performed electron doping by liquid-ionic-gating technique in FeSe thin flake and achieved an enhancement of Tc up to 48 K (from initially ~10K) with continuously increasing the gate voltage to about 4.2 V. At some certain carrier concentration, a Lifshitz transition was suggested as the sample suddenly changed from low-Tc to high-Tc phase. These results could help researchers to pursuit new path for exploring higher Tc in these materials.