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 (T_c) below which the system is superconducting. The low T_c 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 T_c 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 T_c limit (2) in two dimensions (2D).

长期以来，具有无耗散电流的超导状态一直令人着迷，其涉及诸如自发对称性破坏和希格斯现象之类的基本问题，以及从磁共振成像机器的磁铁到量子计算机硬件的各种应用。在经典的Bardeen-Cooper-Schrieffer（BCS）理论中，金属中的电子在转变温度（T _c）下成对存在，在该温度以下，系统超导。BCS超导体的低T _c与电子的一小部分有关，这些电子的量子态通过配对而改变。探索更高T _{c的一种方法}就是要找到其中大部分电子都参与超导的量子材料。在本期的第190页上，中川等人。（1）报告了在新制度下对超导体的实验，它们接近于在二维（2D）上达到理论上预测的T _c极限（2）。