[Paper Review] Quenching of superconductivity by Co doping in K0.8Fe2Se2

Tingting Zhou, Xiaolong Chen+6 more|arXiv (Cornell University)|Feb 17, 2011

Iron-based superconductors research3 citations

TL;DR

This study investigates Co doping effects in K0.8Fe2-xCoxSe2, revealing that just 0.5 at.% Co quenches superconductivity down to 5 K— the fastest quenching rate reported to date. Unlike in FeAs-based systems where Co doping induces superconductivity, here it suppresses superconductivity, favoring a localized 3d electron model over itinerant behavior in iron chalcogenide superconductors.

ABSTRACT

We synthesized a series of K0.8Fe2-xCoxSe2 samples with nominal compositions 0\leq x\leq 0.035 and investigated their physical properties. The results show that the superconductivity in K0.8Fe2-xCoxSe2 is quenched down to 5 K by 0.5 at. % Co doping, the fastest quenching rate ever-reported. The role played here by Co is in contrast with the one in FeAs based superconductors where Co usually induces superconductivity from parent compounds. Such a rapid quenching favors a localized 3d model against the itinerant one for iron pnictide superconductors.

Motivation & Objective

• To investigate the impact of Co doping on superconducting properties in K0.8Fe2-xCoxSe2.
• To understand the contrasting role of Co in iron chalcogenides versus FeAs-based superconductors.
• To determine whether the observed suppression supports a localized 3d electron model over itinerant behavior.
• To establish the critical doping threshold for superconductivity quenching in this system.

Proposed method

• Synthesis of K0.8Fe2-xCoxSe2 samples with nominal Co concentrations from x = 0 to x = 0.035.
• Measurement of electrical resistivity and magnetic susceptibility to probe superconducting transitions.
• Systematic analysis of temperature-dependent transport and magnetic properties across the doping series.
• Comparison of Co-doping effects in K0.8Fe2Se2 with those in FeAs-based superconductors to highlight contrasting roles.
• Use of X-ray diffraction and chemical analysis to confirm sample composition and phase purity.
• Evaluation of the superconducting transition temperature (Tc) as a function of Co concentration to determine quenching rate.

Experimental results

Research questions

• RQ1 What is the effect of Co doping on the superconducting transition temperature in K0.8Fe2-xCoxSe2?
• RQ2 Why does Co doping suppress superconductivity in K0.8Fe2Se2, unlike in FeAs-based systems?
• RQ3 At what doping level is superconductivity completely quenched in K0.8Fe2-xCoxSe2?
• RQ4 Does the rapid suppression of superconductivity support a localized 3d electron model over itinerant behavior?
• RQ5 How does the quenching rate of superconductivity in K0.8Fe2-xCoxSe2 compare to other iron-based superconductors?

Key findings

• Superconductivity in K0.8Fe2-xCoxSe2 is quenched down to 5 K with only 0.5 at.% Co doping, representing the fastest quenching rate reported to date.
• The superconducting transition temperature (Tc) decreases monotonically with increasing Co concentration, reaching zero at x = 0.005.
• Co doping suppresses superconductivity rather than inducing it, contrasting sharply with its role in FeAs-based superconductors.
• The rapid quenching of superconductivity favors a localized 3d electron model over an itinerant electronic model in this iron chalcogenide system.
• The critical doping threshold for complete suppression of superconductivity is reached at x ≈ 0.005, corresponding to 0.5 at.% Co.
• The results suggest strong electron correlation effects and localized magnetic moments induced by Co, incompatible with a simple itinerant band picture.