**The Superconducting Transition Temperatures of Fe _{1+x}Se_{1-y}, Fe_{1+x}Se_{1-y}Te_{y} and (K/Rb/Cs)_{z}Fe_{2-x}Se_{2})**, D. R. Harshman and A. T. Fiory [arXiv]

In a recent contribution to this journal, it was shown that the transition temperatures of optimal high-*T*c compounds obey the algebraic relation, *T*_{C0} = k_{B}^{–1}β/ℓζ, where ℓ is related to the mean spacing between interacting charges in the layers, ζ is the distance between interacting electronic layers, β is a universal constant and k_{B} is Boltzmann’s constant. The equation was derived assuming pairing based on interlayer Coulomb interactions between physically separated charges. This theory was initially validated for 31 compounds from five different high-*T*_{C} families (within an accuracy of ±1.37 K). Herein we report the addition of Fe_{1+x}Se_{1–y} and Fe_{1+x}Se_{1–y}Te_{y} (both optimized under pressure) and A_{z}Fe_{2–x}Se_{2} (for A = K, Rb, or Cs) to the growing list of Coulomb-mediated superconducting compounds in which T_{C0} is determined by the above equation. Doping in these materials is accomplished through the introduction of excess Fe and/or Se deficiency, or a combination of alkali metal and Fe vacancies. Consequently, a very small number of vacancies or interstitials can induce a superconducting state with a substantial transition temperature. The confirmation of the above equation for these Se-based Fe chalcogenides increases to six the number of superconducting families for which the transition temperature can be accurately predicted.

D. R. Harshman and A. T. Fiory, J. Phys.: Condens. Matter **24**, 135701 (2012).