Structure, superconductivity, and magnetism in Rb1−xFe1.6Se2−zSz

Abstract

We report on single-crystal growth, stoichiometry, structure and basic characterization of Rb1−xFe2−ySe2−zSz crystals where Se is substituted by S. The temperature and magnetic field dependence of magnetic and thermodynamic properties of all samples was studied by differential-scanning calorimetry, magnetic susceptibility, electrical conductivity, and specific heat. The experimental results are discussed within a T−z phase diagram, which includes vacancy-ordered and vacancy-disordered antiferromagnetic (AFM), superconducting (SC), and nonsuperconducting phases. The structural study reveals change in the local environment of the Fe tetrahedrons depending on substitution: a reduction of the Fe-Fe and Fe-Ch(chalcogen) bond lengths and a tendency for six out- of eight bond angles to approach values realizing a regular tetrahedron and hence, suggesting a reduction of structural distortions with substitution. With increasing substitution, a nonmonotonic decrease of the superconducting transition temperature Tc was observed; the SC state disappears at a substitution level above z=1.2. The SC state coexists with the AFM state that persists in all samples independent of substitution. The transition temperature into the AFM state, TN, decreases gradually with increasing substitution indicating a weakening of the AFM interactions. The AFM phase exhibits an iron-vacancy-ordered structure below the structural transition temperature Ts. Ts shows a nonmonotonous variation: a decrease with increasing z up to 1.3, followed by an increase on further increasing z. The electronic specific heat reveals a significant reduction of the anomaly at the SC transition temperature indicating a reduction of the density of states at the Fermi energy and a weakening of the electronic correlations that can explain the suppression of the superconductivity with substitution.

Source-reported materials — not catalogue approval

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