With superconducting diodes, researchers advance work towards ultra-efficient quantum electronic devices

Originally, the concept of a superconducting diode was predicted with an external magnetic field, which has some fundamental limitations. In the new experiments at Brown, Li’s team created an extremely powerful diode effect without a magnetic field. When turning on an electric current in one direction, the system almost immediately becomes a resistance, while it remains a superconductor in the opposite direction.

The system creates a unique situation with a diode effect without an external magnetic field in a single superconductor. The results support a hypothesis theorized by study co-author Mathias Scheurer, a theoretical physicist at the University of Innsbruck in Australia, that superconductivity and magnetism can co-exist in a system composed of three twisted graphene layers. against each other. The system can generate its own internal magnetic field, creating a diode effect.

Additionally, the team was able to reverse the direction of the diode using a simple electric field.

“The demonstration of the field-free diode effect in a homogeneous superconductor creates a wonderful opportunity to explore the possible application of a device,” Li said. “And the additional experimental control we demonstrated adds more possibilities. to design a programmable diode array without dissipation.”

A promising material

The diode effect was produced using graphene, a material made up of a single layer of carbon atoms arranged in a honeycomb. Stacking multiple layers of graphene leads to completely new properties, including the ability of three layers of graphene twisted against each other to conduct electrical current without loss. This has been demonstrated in previous experiments conducted by Li and his collaborators.

The fact that a superconducting diode effect can exist without an external magnetic field in this system has important implications for studying the complex physical behavior of twisted three-layer graphene. It demonstrates the coexistence of superconductivity and magnetism.

“Superconductivity and ferromagnetism generally occupy opposite ends of the material spectrum,” said Jiang-Xiazi Lin, postdoctoral researcher at Brown and one of the study’s lead authors. “The coexistence between these two quantum phases is rare, and it is almost synonymous with exciting physics.”

Phum Siriviboon, who conducted research in Li’s lab as an undergraduate and earned a bachelor’s degree from Brown in May 2022, was the study’s other lead author: “This is the first time that the coexistence between superconductivity and ferromagnetism is observed in two dimensions. materials,” Siriviboon said. “Our result establishes a new method to study the interaction between superconductivity and ferromagnetism.”

The team’s latest research demonstrates that the observed diode effect not only has technological relevance, but also has the potential to improve understanding of fundamental processes in many-body physics. Li and Scheurer, along with Harley D. Scammell of the University of New South Wales, published the theoretical basis for this phenomenon in a 2022 paper. This theoretical work indicates the next stage of the team’s work, which is to examine the dependence of the superconducting diode effect when electric currents flow in different directions.

“Phum and Jiang-Xiazi have been a wonderful team working together,” Li said. essential.”

This story was written by Pete Bilderback and based on content provided by the University of Innsbruck.

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