The field of quantum condensed-matter physics has been recently mired with exciting discoveries, one of which is the superconducting diode effect. Researchers from the University of Wollongong and Monash University, collaborating under FLEET, have thoroughly reviewed this intriguing phenomenon. The superconducting diode effect paves the way for dissipationless supercurrent to flow in a singular direction. Its discovery holds immense promise for the development of ultra-low energy superconducting and semiconducting-superconducting hybrid quantum devices. These advancements have the potential to revolutionize both classical and quantum computing.
The Marvels of Superconductivity
Superconductivity is characterized by zero resistivity and perfect diamagnetic behavior. These unique properties result in dissipationless transport and the phenomenon of magnetic levitation. Traditional superconductors, as well as low-temperature superconductivity, are elucidated by the microscopic Bardeen-Cooper-Schrieffer (BCS) theory established in 1957. However, the predictions of the Fulde-Ferrell-Larkin-Ovchinnikov ferromagnetic superconducting phase in 1964-65, along with the discovery of “high-temperature” superconductivity in antiferromagnetic structures in 1986-87, have spearheaded the exploration of unconventional superconductivity. Unconventional superconductivity deals with stabilizing superconducting order in functional materials such as magnetic superconductors, ferroelectric superconductors, and topological superconductors.
The Flow of Cooper Pairs
Unlike conventional semiconductors and normal conductors, superconductors exhibit pair formation among electrons, known as Cooper pairs. The flow of these Cooper pairs is termed as supercurrent. Recent research has demonstrated nonreciprocal supercurrent transport, leading to the emergence of diode effects in various superconducting materials with different geometric structures, such as single crystals, thin films, heterostructures, nanowires, and Josephson junctions. The FLEET research team has delved into this fascinating area, presenting a comprehensive review of both theoretical and experimental progress in the superconducting diode effect (SDE), while also providing insights into future prospects. The study encompasses an examination of various materials that host SDE, device structures, theoretical models, as well as the symmetry requirements for different physical mechanisms that give rise to SDE.
What sets the superconducting diode apart from its conventional semiconducting counterpart is its remarkable efficiency, which can be finely controlled and tuned using extrinsic stimuli. Factors such as temperature, magnetic field, gating, device design, and the intrinsic quantum mechanical functionalities including Berry phase, band topology, and spin-orbit interaction play a significant role in governing the efficiency of the SDE. Dr. Muhammad Nadeem, a Research Fellow at FLEET from the University of Wollongong, emphasizes this tunability stating, “Unlike the conventional semiconducting diode, the efficiency of SDE is widely tunable via extrinsic stimuli such as temperature, magnetic field, gating, device design and intrinsic quantum mechanical functionalities such as Berry phase, band topology and spin-orbit interaction.”
Achieving Control: Magnetic Fields and Gate Electric Fields
The direction of supercurrent in a superconducting diode can be precisely controlled using either a magnetic field or a gate electric field. This development opens up new possibilities for novel device applications in superconducting and semiconducting-superconducting hybrid technologies. Professor Michael Fuhrer, the Director of FLEET from Monash University, emphasizes the potential impact of gate-tunable diode functionalities in field-effect superconducting structures, stating, “The gate-tunable diode functionalities in the field-effect superconducting structures could allow novel device applications for superconducting and semiconducting-superconducting hybrid technologies.”
The superconducting diode effect has been observed in a diverse range of superconducting structures, including those made from conventional superconductors, ferroelectric superconductors, twisted few-layer graphene, van der Waals heterostructures, and topological superconductors. This evidence highlights the vast potential and widespread usability of superconducting diodes, effectively diversifying the landscape of quantum technologies. Professor Xiaolin Wang, a Chief Investigator of FLEET from the University of Wollongong, affirms this notion, stating, “It reflects the enormous potential and wide usability of superconducting diodes, which markedly diversifies the landscape of quantum technologies.”
The exploration of the superconducting diode effect delves into the realm of quantum condensed-matter physics. Collaborative research efforts from FLEET researchers at the University of Wollongong and Monash University have shed light on this mesmerizing phenomenon and its potential applications. Moving forward, continued research and development in this area will unlock even more possibilities for ultra-low energy superconducting and semiconducting-superconducting hybrid quantum devices. The superconducting diode effect offers the prospect of revolutionizing classical and quantum computing, thereby shaping the future of technology.