Anomalous normal state gap in an electron-doped cuprate

In the underdoped n-type cuprate Nd2-xCexCuO4, long-ranged antiferromagnetic order reconstructs the Fermi surface, resulting in a putative antiferromagnetic metal with small pockets. Using angle-resolved photoemission spectroscopy, we observe an anomalous energy gap, an order of magnitude smaller than the antiferromagnetic gap, in a wide range of the underdoped regime and smoothly connecting to the superconducting gap at optimal doping. After carefully considering all the known ordering tendencies in tandem with the phase diagram, we hypothesize that the normal state gap in the underdoped n-type cuprates originates from Cooper pairing. The high temperature scale of the normal state gap raises the prospect of engineering higher transition temperatures in the n-type cuprates comparable to that of the p-type cuprates.在欠掺杂n型铜酸盐Nd₂₋ₓCeₓCuO₄中，长程反铁磁有序会重构费米面（Fermi surface），进而形成一种具有小费米口袋的推定反铁磁金属。借助角分辨光电子能谱（angle-resolved photoemission spectroscopy），我们在欠掺杂区域的宽范围内观测到一个反常能隙——其尺度较反铁磁能隙小一个数量级，且该能隙在最佳掺杂点处与超导能隙平滑衔接。在综合考量所有已知的有序趋势与相图后，我们提出假说：欠掺杂n型铜酸盐的正常态能隙起源于库珀配对（Cooper pairing）。该正常态能隙的高温特征尺度为在n型铜酸盐中调控获得可与p型铜酸盐媲美的更高转变温度提供了可能。