This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Superconductors can carry electrical current without resistance, but only up to a maximum value known as the critical current. The critical current is a crucial figure of merit for applications, and materials science has long been focused on increasing this limit.
Researchers at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) have now shown that, in type-II superconductors, this conventional limit can be exceeded when the current is applied for only a few picoseconds. On these ultrashort timescales, the researchers were able to access a much higher, intrinsic limit known as the depairing current. The work has now been published in Nature Physics.
Superconductivity is one of the most striking collective phenomena in quantum materials. When certain materials are cooled below a characteristic transition temperature, their electrical resistance vanishes, and electric current can flow without dissipating energy as heat. This unusual behavior arises because electrons form correlated pairs, known as Cooper pairs, which move collectively through the material like a wave.
Superconductors are therefore attractive for technologies ranging from powerful magnets and sensitive detectors to quantum circuits. However, this dissipationless state has its limits: If the current becomes too large, superconductivity breaks down. The critical current is a key property of any superconductor, defining the maximum current it can carry before electrical dissipation appears.
In type-II superconductors, however, this experimentally observed limit is often not determined directly by the microscopic properties of the superconducting state. Instead, it is typically governed by the motion of vortices—tiny regions through which magnetic flux penetrates the material. At sufficiently high current, the vortices start to move, generating resistance and heat that can push the material out of its superconducting state.
Yet a superconductor has a higher, intrinsic current limit: the depairing current. "One way to picture it is that the current 'twists' the phase of the coherent quantum state of the superconductor, rather like winding a spring," explains Eryin Wang, lead author of the study. If the superconducting condensate is twisted too far, the superconducting state becomes unstable.
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