Fig. 5: Phase diagram of FeSe/STO.
From: Incommensurate smectic phase in close proximity to the high-Tc superconductor FeSe/SrTiO3
a Schematic of electronic structures in different layers of FeSe. The 1 UC FeSe/STO is a high-Tc superconductor. Smectic phase with long-range stripe ordering is established in 2 UC FeSe films. 3 UC FeSe is in nematic phase with strong smectic fluctuation. Short-range stripes are pinned by defects. b Phase diagram of FeSe/STO as a function of temperature, thickness, and electron doping. The smectic phase may persist in 1 UC FeSe/STO once the electron doping is partially removed. In reality, by a large amount of electron doping from STO (0.12 electron/Fe), smectic phase is suppressed and high-Tc superconductivity (SC-I) emerges in 1 UC FeSe, in which the residual smectic instability provides additional Tc enhancement. In multilayer FeSe/STO, the superconducting states can be achieved by surface doping of alkali metals. The red balls denote the optimal Tc obtained from ARPES results38,39,52,53.
