**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).