This article is cited in 3 papers

CONDENSED MATTER

Comparison of the superconducting properties of potassium iron selenides with isovalent substitution

T. E. Kuzmicheva^a, S. A. Kuzmichev^ba, A. D. Ilina^a, I. A. Nikitchenkov^ba, E. O. Rakhmanov^ca, A. I. Shilov^a, I. V. Morozov<sup>a

a</sup> Lebedev Physical Institute, Russian Academy of Sciences, Moscow, 119991 Russia
^b Faculty of Physics, Moscow State University, Moscow, 119991 Russia
^c Faculty of Chemistry, Moscow State University, Moscow, 119991 Russia

Abstract: Using incoherent multiple Andreev reflection effect spectroscopy, we have studied the properties of the superconducting phase of (K,Na)$_x$Fe$_{2-y}$Se$_2$ and K$_z$Fe$_{2-y}$(Se,S)$_2$ iron selenides with critical temperatures ${{T}_{c}} \approx 27{-} 31$ K. In both compositions, we directly show a presence of a single superconducting order parameter, and directly determine its magnitude and temperature dependence. The obtained characteristic ratio $2\Delta (0){\text{/}}{{k}_{B}}{{T}_{c}} \approx 4.1{-} 4.6$ results from a strong coupling in the electron bands. The similarity between the superconducting gap structure and the observed $\Delta (0)$ scaling with critical temperature points to a uniform Cooper pairing mechanism in (K,Na)$_x$Fe$_{2-y}$Se$_2$ and K$_z$Fe$_{2-y}$(Se,S)$_2$ iron selenides.

Received: 10.03.2025
Revised: 24.03.2025
Accepted: 24.03.2025

DOI: 10.31857/S0370274X25040241

 English version: Journal of Experimental and Theoretical Physics Letters, 2025, 121:8, 662–669