In the vast field of quantum condensed-matter physics, a group of researchers from the University of Wollongong and Monash University came together in a collaborative effort to review an extraordinary phenomenon known as the superconducting diode effect (SDE). This groundbreaking discovery has captivated the attention of scientists and is expected to pave the way for future advancements in superconducting and semiconducting-superconducting hybrid quantum devices. With immense potential applications in classical and quantum computing, the SDE allows dissipationless supercurrent to flow exclusively in one direction, unlocking a myriad of new functionalities.
Superconductivity, characterized by zero resistivity and perfect diamagnetic behavior, is the defining feature of a superconductor. Its unique properties enable dissipationless transport and even magnetic levitation. Since the seminal work of Bardeen, Cooper, and Schrieffer (BCS) in 1957, “conventional” superconductors operating at low temperatures have been extensively studied and well-explained. However, the advent of unconventional superconductivity has brought forth new and exciting possibilities. From the prediction of the Fulde-Ferrell-Larkin-Ovchinnikov ferromagnetic superconducting phase to the discovery of “high-temperature” superconductivity, researchers have expanded the boundaries of superconducting materials, uncovering functionalities in systems such as magnetic superconductors, ferroelectric superconductors, and topological superconductors.
Unlike traditional semiconductors and normal conductors, electrons in superconductors exist as pairs known as Cooper pairs. The flow of these Cooper pairs is referred to as a supercurrent. In recent years, scientists have made remarkable observations of nonreciprocal supercurrent transport, leading to the emergence of the superconducting diode effect. This revolutionary phenomenon has been observed across various superconducting materials, including single crystals, thin films, heterostructures, nanowires, and Josephson junctions. The ability to alter and manipulate the direction of supercurrent using external stimuli such as temperature, magnetic fields, gating, device design, and intrinsic quantum mechanical functionalities has made the SDE highly versatile and efficient.
In their meticulous review, the FLEET research team not only analyzed the existing theoretical and experimental progress in the SDE but also offered a promising outlook for future advancements. The study sheds light on the diverse range of materials that exhibit the SDE, the various device structures that support it, and the symmetry requirements for different physical mechanisms underlying the effect. Unlike conventional semiconducting diodes, the efficiency of the SDE can be fine-tuned through extrinsic stimuli and intrinsic quantum mechanical properties like Berry phase, band topology, and spin-orbit interaction. This remarkable feature opens up new possibilities for novel device applications in the realm of superconducting and semiconducting-superconducting hybrid technologies.
The ubiquity of the superconducting diode effect is truly astonishing. It has been observed in a wide range of superconducting structures, including conventional superconductors, ferroelectric superconductors, twisted few-layer graphene, van der Waals heterostructures, and helical or chiral topological superconductors. This versatility showcases the vast potential and broad usability of superconducting diodes, propelling the landscape of quantum technologies into exciting new frontiers. As Prof. Xiaolin Wang, Chief Investigator of FLEET, aptly puts it, “the enormous potential and wide usability of superconducting diodes markedly diversifies the landscape of quantum technologies.”
The superconducting diode effect stands as a testament to the unending quest of scientists to unravel the mysteries of the quantum world. With its ability to enable dissipationless supercurrent flow in one direction, this remarkable phenomenon offers unlimited possibilities for future quantum technologies. From ultra-low energy superconducting circuits to semiconducting-superconducting hybrid quantum devices, the SDE holds the key to unlocking the full potential of classical and quantum computing. As researchers continue to push the boundaries of what is possible, the future of quantum technologies shines brighter than ever before.
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