Switching superconductivity on and off with stress and magnetism

As industrial computing needs grow, the size and energy consumption of the hardware needed to keep up with those needs grows as well. A possible solution to this dilemma could be found in superconducting materials, which can reduce that energy consumption exponentially. Imagine cooling a giant data center full of constantly running servers down to nearly absolute zero, enabling large-scale computation with incredible energy efficiency.

Physicists at the University of Washington and the US Department of Energy (DOE)’s Argonne National Laboratory have made a discovery that could help bring about this more efficient future. They have found a superconducting material that is uniquely sensitive to outside stimuli, allowing its superconducting properties to be enhanced or suppressed at will. This could lead to new opportunities for energy-efficient switchable superconducting circuits. The physicists report their discovery in a paper in Science Advances.

Superconductivity is a quantum mechanical phase of matter in which an electrical current can flow through a material with zero resistance, leading to perfect electronic transport efficiency. Superconductors are already used in the most powerful electromagnets for advanced technologies such as magnetic resonance imaging, particle accelerators, fusion reactors and even levitating trains. They have also found uses in quantum computing.

Today’s electronics use semiconducting transistors to quickly switch electric currents on and off, creating the binary ones and zeroes used in information processing. As these currents must flow through materials with finite electrical resistance, some of the energy is wasted as heat. This is why your computer heats up over time. The low temperatures needed for superconductivity, usually more than 200°F below freezing, makes those materials impractical for use in hand-held devices. However, they could conceivably be useful on an industrial scale.

The research team, led by Shua Sanchez at the University of Washington, examined an unusual superconducting material with exceptional tunability. This crystal is made of flat sheets of ferromagnetic europium atoms sandwiched between superconducting layers of iron, cobalt and arsenic atoms. Finding ferromagnetism and superconductivity together in nature is extremely rare, according to Sanchez, as one phase usually overpowers the other.

“It is actually a very uncomfortable situation for the superconducting layers, as they are pierced by the magnetic fields from the surrounding europium atoms,” Sanchez said. “This weakens the superconductivity and results in a finite electrical resistance.”

To understand the interaction of these phases, Sanchez spent a year as a resident at a leading X-ray light source, the Advanced Photon Source (APS), a DOE Office of Science user facility at Argonne. Working with physicists at APS beamlines 4-ID and 6-ID, Sanchez developed a comprehensive characterization platform capable of probing the microscopic details of complex materials.

Using a combination of X-ray techniques, Sanchez and his collaborators were able to show that applying a magnetic field to the crystal can reorient the europium magnetic field lines to run parallel to the superconducting layers. This removes their antagonistic effects and causes a zero-resistance state to emerge. Using electrical measurements and X-ray scattering techniques, the researchers were able to confirm that they could control the behavior of the material.

“The nature of independent parameters controlling superconductivity is quite fascinating, as one could map out a complete method of controlling this effect,” said Argonne’s Philip Ryan, a co-author of the paper. “This potential posits several fascinating ideas including the ability to regulate field sensitivity for quantum devices.”

The team then applied stresses to the crystal, with interesting results. They found the superconductivity could be either boosted enough to overcome the magnetism even without re-orienting the field or weakened enough that the magnetic reorientation could no longer produce the zero-resistance state. This additional parameter allows for the material’s sensitivity to magnetism to be controlled and customized.

“This material is exciting because you have a close competition between multiple phases, and by applying a small stress or magnetic field, you can boost one phase over the other to turn the superconductivity on and off,” Sanchez said. “The vast majority of superconductors aren’t nearly as easily switchable.”

This story is adapted from material from Argonne National 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.