Limits on superconductivity in flatland

Limits on superconductivity in flatland
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Summary

The superconducting state, with dissipationless electrical current flow, has long been a source of fascination, with implications for fundamental questions like spontaneous symmetry breaking and the Higgs phenomena, as well as for applications ranging from magnets for magnetic resonance imaging machines to hardware for quantum computers. In the classic Bardeen-Cooper-Schrieffer (BCS) theory, electrons in a metal form pairs at a transition temperature (Tc) below which the system is superconducting. The low Tc of BCS superconductors is related to the small fraction of electrons that have their quantum states modified by pairing. One route to exploring a higher Tc is to find quantum materials in which a larger fraction of the electrons get involved in superconductivity. On page 190 of this issue, Nakagawa et al. (1) report experiments on superconductors in a new regime, where they come close to achieving the theoretically predicted Tc limit (2) in two dimensions (2D).