The superconducting diode effect, a quantum effect that allows dissipationless supercurrent to flow in only one direction, has been reviewed by scientists. The SDE adds new capabilities to superconducting circuits and future ultra-low energy superconducting/hybrid devices, with applications in both classical and quantum computing.
The superconducting diode effect, one of the most fascinating phenomena recently discovered in quantum condensed-matter physics, has been reviewed by FLEET researchers from the University of Wollongong and Monash University.
A superconducting diode allows supercurrent to flow in only one direction and adds new functionality to superconducting circuits. This non-dissipative circuit element will be essential in future ultra-low energy superconducting and semiconducting-superconducting hybrid quantum devices, with quantum technologies having applications in both classical and quantum computing.
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.
Dr. Muhammad Nadeem
SUPERCONDUCTORS AND DIODE EFFECTS
A superconductor is characterized by zero resistivity and perfect diamagnetic behavior, which leads to dissipationless transport and magnetic levitation.
‘Conventional’ superconductors and the underlying phenomenon of low-temperature superconductivity are explained well by microscopic Bardeen-Cooper-Schrieffer (BCS) theory proposed in 1957.
The prediction of Fulde-Ferrell-Larkin-Ovchinnikov ferromagnetic superconducting phase in 1964-65 and the discovery of ‘high-temperature’ superconductivity in antiferromagnetic structures in 1986-87, has set the stage for the field of unconventional superconductivity wherein superconducting order can be stabilized in functional materials such as magnetic superconductors, ferroelectric superconductors, and helical or chiral topological superconductors.
In superconductors, unlike conventional semiconductors and normal conductors, electrons form pairs known as Cooper pairs, and the flow of Cooper pairs is referred to as a supercurrent. Researchers have recently observed nonreciprocal supercurrent transport leading to diode effects in a variety of superconducting materials with varying geometric structures and designs, such as single crystals, thin films, heterostructures, nanowires, and Josephson junctions.
THE STUDY
The FLEET research team reviewed theoretical and experimental progress in the superconducting diode effect (SDE) and provided a prospective analysis of future aspects. This study sheds light on various materials hosting SDE, device structures, theoretical models, and symmetry requirements for different physical mechanisms leading to SDE.
“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,” explains Dr. Muhammad Nadeem (University of Wollongong), who is a Research Fellow at FLEET.
A magnetic field or a gate electric field can be used to control the direction of supercurrent. “The gate-tunable diode functionalities in the field-effect superconducting structures could allow novel device applications for superconducting and semiconducting-superconducting hybrid technologies,” says co-author and FLEET Director Prof Michael Fuhrer (Monash University).
SDE has been observed in a variety of superconducting structures, including those made of conventional superconductors, ferroelectric superconductors, twisted few-layer graphene, van der Waals heterostructures, and helical or chiral topological superconductors. It reflects the enormous potential and broad applicability of superconducting diodes, which significantly diversifies the landscape of quantum technologies, according to FLEET Chief Investigator Prof Xiaolin Wang (University of Wollongong).
