Scientists from the University of Wollongong and Monash University have collaborated to review the superconducting diode effect, a recent discovery in quantum condensed-matter physics. This phenomenon allows dissipationless supercurrent to flow in only one direction, presenting new possibilities for superconducting circuits. The development of superconducting diodes is crucial for the advancement of ultra-low energy superconducting and semiconducting-superconducting hybrid quantum devices, with potential applications in both classical and quantum computing.
The Unique Characteristics of Superconductors
Superconductors are known for their zero resistivity and perfect diamagnetic behavior, which enable dissipationless transport and magnetic levitation. Traditional superconductors and low-temperature superconductivity are well explained by the Bardeen–Cooper–Schrieffer (BCS) theory proposed in 1957. However, the prediction of unconventional superconductivity and the discovery of high-temperature superconductivity in antiferromagnetic structures have paved the way for the exploration of functional materials that exhibit superconducting order, such as magnetic superconductors and ferroelectric superconductors.
The Superconducting Diode Effect
Unlike conventional semiconductors and normal conductors, superconductors consist of pairs of electrons called Cooper pairs. The flow of Cooper pairs is referred to as a supercurrent. Researchers have recently observed the nonreciprocal supercurrent transport, leading to diode effects in various superconducting materials, including single crystals, thin films, heterostructures, nanowires, and Josephson junctions.
Analyzing the Potential
The research team from FLEET has conducted a comprehensive review of the theoretical and experimental progress in the superconducting diode effect (SDE) and provided insights into future aspects of this fascinating phenomenon. The study highlights various materials that host the SDE, device structures, theoretical models, and symmetry requirements for different physical mechanisms that result in the SDE. The efficiency of the SDE can be adjusted through extrinsic stimuli, such as temperature, magnetic field, gating, device design, and intrinsic quantum mechanical functionalities like Berry phase, band topology, and spin-orbit interaction.
Controlling the Direction of Supercurrent
The direction of supercurrent in a superconducting diode can be controlled either with a magnetic field or a gate electric field. The gate-tunable diode functionalities in field-effect superconducting structures have the potential to unlock novel device applications for superconducting and semiconducting-superconducting hybrid technologies. This level of control and tunability highlights the versatility of superconducting diodes.
The superconducting diode effect has been observed in various superconducting structures, spanning from conventional superconductors to ferroelectric superconductors, twisted few-layer graphene, van der Waals heterostructures, and helical or chiral topological superconductors. This wide range of materials reflects the immense potential and versatility of superconducting diodes, opening up new possibilities and diversifying the landscape of quantum technologies.
Dr. Muhammad Nadeem, a Research Fellow at FLEET from the University of Wollongong, emphasizes that the efficiency of the SDE is tunable through various stimuli and quantum mechanical functionalities. Professor Michael Fuhrer, Director of FLEET from Monash University, notes that the gate-tunable diode functionalities in field-effect superconducting structures have the potential for novel device applications. Professor Xiaolin Wang, a Chief Investigator of FLEET from the University of Wollongong, highlights the enormous potential and wide usability of superconducting diodes in advancing quantum technologies.
The discovery and analysis of the superconducting diode effect have provided valuable insights into a fascinating phenomenon within quantum condensed-matter physics. The ability to control and manipulate dissipationless supercurrent in one direction opens up new possibilities for the development of ultra-low energy superconducting and semiconducting-superconducting hybrid quantum devices. The wide range of materials and the tunability of the superconducting diode effect showcase the potential for advancements in both classical and quantum computing. As researchers continue to explore this field, the future of superconducting diodes looks promising, with numerous exciting applications awaiting discovery.