Magnetism helps provide ‘pairing glue’ in iron-based superconductor

"A metal becomes a superconductor when normal electrons form what physicists call Cooper pairs. The interactions responsible for this binding are often referred to as 'pairing glue'. Determining the nature of this glue is the key to understanding, optimizing and controlling superconducting materials."Ruslan Prozorov, Ames Laboratory

A team led by scientists at the US Department of Energy's Ames Laboratory has shed more light on the nature of high-temperature iron-based superconductivity. They report their findings in a paper in npj Quantum Materials.

Current theories suggest that magnetic fluctuations play a very significant role in determining superconducting properties, and even act as a ‘pairing glue’ in iron-based superconductors.

"A metal becomes a superconductor when normal electrons form what physicists call Cooper pairs," said Ruslan Prozorov, an Ames Laboratory physicist who is an expert in superconductivity and magnetism. "The interactions responsible for this binding are often referred to as 'pairing glue'. Determining the nature of this glue is the key to understanding, optimizing and controlling superconducting materials."

The scientists, from Ames Laboratory, the University of Minnesota, Nanjing University in China and L'École Polytechnique in France, focused their attention on high quality single crystal samples of one widely studied family of iron arsenide high-temperature superconductors. They sought an experimental approach that could systematically disrupt the magnetic, electronic and superconducting ordered states in this material, while keeping the magnetic field, temperature and pressure unchanged.

They chose a not-so-obvious approach – deliberately inducing disorder in the crystal lattice, but in a controlled and quantifiable way. This was performed at the SIRIUS electron accelerator at École Polytechnique. The scientists bombarded their samples with electrons moving at 10% the speed of light, creating collisions that displaced atoms and resulted in desired ‘point-like’ defects.

This approach, adopted at Ames Laboratory in the early stages of iron superconductivity research, provides a way to poke or nudge the system and measure its response. "Think about it as another 'knob' that we can turn, leaving other important parameters unchanged," said Prozorov.

In previous and related research reported in a 2018 paper in Nature Communications, which used a similar approach of probing the system by disorder, the team looked at the co-existence and interplay of superconductivity and charge-density wave (CDW), another quantum order that competes with superconductivity, in a niobium diselenide (NbSe₂) superconductor. They found an intricate relationship in which CDW competes for the same electronic states but also helps superconductivity by softening the phonon modes that play the role of a superconducting glue.

In the present work, itinerant magnetism (spin-density wave) also competes with superconductivity for the electronic states, but offers magnetic fluctuations as a glue. The team found that the added disorder resulted in a substantial suppression of both magnetic order and superconductivity, pointing to a nontrivial role of magnetism in high-temperature superconductivity.

This story is adapted from material from Ames Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.