Improving quantum-transition temperatures in BaFe2As2-based crystals by removing local-lattice strain & electronic-structure disorder

TL;DR

This study demonstrates that thermal annealing enhances transition temperatures in BaFe2As2-based crystals by reducing local-lattice strain and electronic disorder, leading to improved magnetic and superconducting properties.

Contribution

It reveals how removing local lattice strain and electronic disorder through annealing can significantly improve quantum transition temperatures in BaFe2As2-based materials.

Findings

Annealing increases Neel temperature from 132 K to 136 K in BaFe2As2.

Annealing raises superconducting transition temperature from 23 K to 25 K in cobalt-doped BaFe2As2.

Annealing promotes local chemical uniformity and nanoscale phase separation, enhancing superconducting properties.

Abstract

Quantum materials such as antiferromagnets or superconductors are complex in that chemical, electronic, and spin phenomena at atomic scales can manifest in their collective properties. Although there are some clues for designing such materials, they remain mainly unpredictable. In this work, we find that enhancement of transition temperatures in BaFe2As2-based crystals are caused by removing local-lattice strain and electronic-structure disorder by thermal annealing. While annealing improves Neel-ordering temperature in BaFe2As2 crystal (TN=132 K to 136 K) by removing in-plane electronic defects and overall reduction of a-lattice parameter, it increases superconducting-ordering temperature in optimally cobalt-doped BaFe2As2 crystal (Tc=23 to 25 K) by precipitating-out the cobalt dopants and giving larger overall a-lattice parameter. Although annealing promotes local chemical and electronic uniformity resulting in higher TN in the parent, it results in nanoscale phase separation in the superconductor resulting in lower disparity and strong superconducting band gaps in the dominant crystalline regions, which lead to both higher overall Tc and critical-current-density, Jc.