ARPES study of cesium-coated FeSe thin films on SrTiO₃

Temperature insensitivity of Fermi surface in electron-doped high-temperature FeSe films on SrTiO3

“…1(b). The electron carrier concentration (n e ) estimated from the size of the electron pocket g is ~0.1 electrons/Fe which is close to the optimal doping where the highest T c of ~ 40 K is realized [25]. It is noted that, while there is another hole-like band (a 2 ) approaching E F near the G point [see finite intensity near the G point in Fig.…”

“…After the fabrication, the film was transferred to the ARPES chamber without exposing to the air. Electron doping necessary for the realization of high-temperature superconductivity was achieved by the Cs deposition onto the film surface at room temperature using a Cs dispenser (SAES Getters) [25]. ARPES measurements were performed in an ultrahigh vacuum better than 5  10 -11 Torr using a Scienta-Omicron SES2002 electron analyzer with a He discharge lamp (hn = 21.218 eV) at Tohoku University.…”

“…1(a) and orange curve in Fig. 1(b)], it comes from interior FeSe layers beneath the topmost layer which remain nearly nondoped even after Cs deposition [25]. Therefore, in the following, we will focus only on the a, a', and g bands originating from the electron-doped topmost FeSe layer to discuss the temperature-induced evolution of the band structure in the electron-doped region.…”

Magic Doping and Robust Superconductivity in Monolayer FeSe on Titanates

“…[ 8 ] This scenario might also explain why most reported high‐quality monolayer FeSe films grown on different types of perovskite titanate substrates [ 5,9,13,19 ] “magically” exhibit similar ≈ 0.11 doping in ARPES, which coincidentally corresponds to the maximum T C found in doped multilayer systems. [ 8,17 ] In the cases of K/Cs dosing or excess Se, additional disorders are introduced and the discreteness is smoothed, making the transitions more continuous and less first‐order‐like. [ 35 ] This leads to a continuous change in Fermi surface volume and T C .…”

“…[ 35 ] This leads to a continuous change in Fermi surface volume and T C . [ 6,8,17,36,37 ] Interestingly, the T C evolution with Na intercalation represents an intermediately smoothed case between Li and K. [ 18 ]…”