Pulsed laser deposition was used to grow c-axis aligned films of La2−xSrxCuO4−δ, with Sr content, x, in the range of 0.03 to 0.2, on substrates prepared from single-crystalline SrLaAlO4, with a lattice mismatch of 0.5%. The thickness dependence of Tc0, the temperature at which the resistance falls to zero, is much reduced compared to that of films deposited on SrTiO3, where the lattice mismatch is 3.4%. The maximum Tc0 is achieved at x=0.15 for both types of substrates. While the thickness dependence is related to the strain resulting from the lattice mismatch, the value of the maximum Tc0 is determined by the oxygen concentration.

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We grew the single crystals of the SnAs-based van der Waals (vdW)-type superconductor NaSn2As2 and systematically measured its resistivity, specific heat, and ultralow-temperature thermal conductivity. The superconducting transition temperature Tc = 1.60 K of our single crystal is 0.3 K higher than that previously reported. A weak but intrinsic anomaly situated at 193 K is observed in both resistivity and specific heat, which likely arises from a charge-densitywave (CDW) instability. Ultralow-temperature thermal conductivity measurements reveal a fullygapped superconducting state with a negligible residual linear term in zero magnetic field, and the field dependence of κ0/T further suggests NaSn2As2 is an s-wave superconductor.

A general feature of unconventional superconductors is the existence of a superconducting dome in the phase diagram as a function of carrier concentration 1 . For the simplest iron-based superconductor FeSe (with transition temperature Tc  8 K) 2 , its Tc can be greatly enhanced by doping electrons via many routes 3-6 , even up to 65 K in monolayer FeSe/SiTiO3 (refs. 7-10). However, a clear phase diagram with carrier concentration for FeSe-derived superconductors is still lacking. Here, we report the observation of a series of discrete superconducting phases in FeSe thin flakes by continuously tuning carrier concentration through the intercalation of Li and Na ions with a solid ionic gating technique 11 . Such discrete superconducting phases are robust against the substitution of Se by 20% S, but are vulnerable to the substitution of Fe by 2% Cu, highlighting the importance of the iron site being intact. A complete superconducting phase diagram for FeSe-derivatives is given, which is distinct from other unconventional superconductors.The discovery of iron-based superconductors sparked a huge renaissance in exploring the mystery of unconventional superconductivity [12][13][14][15] . For the iron arsenides, there always exists a superconducting (SC) dome in the phase diagram, i.e., a continuous increase, maximum, and then decrease of the transition temperature Tc, with charge carrier doping, applied external pressure, or isovalent doping [14][15][16] . Such an

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