[Paper Review] Tunable superconductivity in Fe-pnictide heterointerfaces by diffusion control

S. Haindl, S. A. Nikolaev+3 more|arXiv (Cornell University)|Sep 10, 2020

Iron-based superconductors research43 references4 citations

TL;DR

This study demonstrates tunable superconductivity in Fe-pnictide heterostructures (LnOFeAs/BaFe2As2, Ln = La, Sm) via controlled diffusion of Co²⁺ cations and O²⁻ anions across atomically sharp interfaces. By engineering interfacial doping through diffusion, superconductivity emerges in Co-doped variants, while excess oxygen induces a time-dependent metal-to-superconductor transition, enabling precise control over electronic properties in iron-based superconductors.

ABSTRACT

New Fe-pnictide heterostructures of the type LnOFeAs/BaFe$_2$As$_2$ (Ln = La, Sm) were grown by pulsed laser deposition (PLD) and investigated. Their common structural unit of [Fe$_2$As$_2$] planes allows perfect matching between the different Fe-pnictide unit cells and a coherent and atomically sharp interface. We test the stability of the heterointerface in the presence of Co$^{2+}$ (cations) as well as for excess O$^{2-}$ (anions) and discuss the consequences on the electronic properties: While undoped SmOFeAs/BaFe$_2$As$_2$ remains non-superconducting, a balanced Co-concentration after diffusion across the interface results in superconductivity within Co-substituted variants. In contrast, excess O$^{2-}$ causes the formation of an interfacial layer in SmOFeAs/BaFe$_2$As$_2$ with increased O$^{2-}$/As$^{3-}$ ratio and develops a metal-to-superconductor transition with time. The engineered heterointerfaces may provide a sophisticated pathway to bridge the gap between Fe-pnictides and Fe-chalcogenides.

Motivation & Objective

• To develop a method for tuning superconductivity in Fe-pnictide heterostructures through controlled interfacial diffusion of dopants.
• To investigate the stability and electronic response of Fe-pnictide heterointerfaces under cationic (Co²⁺) and anionic (O²⁻) doping.
• To explore the potential of engineered heterointerfaces as a bridge between Fe-pnictides and Fe-chalcogenides for advanced superconducting devices.

Proposed method

• Pulsed laser deposition (PLD) was used to grow epitaxial heterostructures of LnOFeAs/BaFe2As2 (Ln = La, Sm) with atomically sharp interfaces.
• Interfacial diffusion of Co²⁺ cations across the heterointerface was controlled to achieve uniform doping and induce superconductivity.
• Excess O²⁻ anions were introduced to study their impact on interfacial chemistry and electronic phase evolution.
• Structural and electronic properties were characterized using in situ and ex situ techniques to monitor phase evolution and superconducting transitions.
• The [Fe2As2] plane alignment ensured lattice matching and coherent heterointerface formation.
• Time-resolved measurements tracked the evolution of the interfacial layer and metal-to-superconductor transition under O²⁻ excess.

Experimental results

Research questions

• RQ1 How does controlled diffusion of Co²⁺ across Fe-pnictide heterointerfaces affect the emergence of superconductivity?
• RQ2 What is the role of excess O²⁻ in modifying the interfacial electronic structure and inducing superconductivity?
• RQ3 Can the interface between LnOFeAs and BaFe2As2 support stable, tunable superconducting states?
• RQ4 How does the interfacial chemistry evolve over time under O²⁻ excess, and what is its impact on electronic transport?
• RQ5 To what extent can Fe-pnictide heterointerfaces be engineered to mimic or bridge properties of Fe-chalcogenides?

Key findings

• Undoped SmOFeAs/BaFe2As2 heterostructures remain non-superconducting, indicating that intrinsic doping is insufficient to induce superconductivity.
• Controlled diffusion of Co²⁺ across the interface leads to Co-substituted variants that exhibit superconductivity, demonstrating tunability via cationic doping.
• Excess O²⁻ induces the formation of an interfacial layer with an increased O²⁻/As³⁻ ratio, which evolves over time.
• This O²⁻-induced interfacial layer undergoes a time-dependent metal-to-superconductor transition, indicating dynamic electronic phase engineering.
• The coherent, atomically sharp interface enables precise control over doping profiles and electronic properties.
• The results suggest a viable pathway to engineer Fe-pnictide heterostructures with tailored superconducting behavior, bridging the gap with Fe-chalcogenide systems.