XXIX International Symposium "Nanophysics and Nanoelectronics", Nizhny Novgorod, March 10-14, 2025
Superconductivity

Tunneling spectroscopy of underdoped NaFe$_{1-x}$Co$_x$As pnictides in the normal state

I. A. Nikitchenkov^ab, S. A. Kuzmichev^ab, A. D. Il'ina^b, I. V. Morozov^c, A. I. Shilov^a, E. O. Rakhmanov^ac, T. E. Kuzmicheva<sup>b

a</sup> Lomonosov Moscow State University, Faculty of Physics
^b P. N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow
^c Lomonosov Moscow State University, Faculty of Chemistry

Abstract: Single crystals of underdoped NaFe$_{0.979}$Co$_{0.021}$As pnictides (i. e., with a deficiency of substituting cobalt compared to the compound possessing the maximum critical temperature $T_{\mathrm{c}}$) were studied using tunneling spectroscopy in the superconducting and the normal state. The obtained $dI(V)/dV$-characteristics of tunneling contacts reproducibly showed residual nonlinearity both below and above the critical temperature. This nonlinearity, being unusual for conventional tunneling junction, was not directly related to the superconducting properties and disappeared at $T\approx$ 60 K. Possible origin of this nonlinearity and its potential relation with the nematicity of the electronic subsystem are discussed.

Keywords: high temperature superconductivity, iron arsenide, break-junction, phase diagram.

DOI: 10.61011/FTT.2025.07.61178.11HH-25

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