Normal-state gap in the parent cuprate Pr2 CuO4±δ normal-state gap in the parent cuprate Pr . He, Wei, Zhang, Shan, Yuan, Zhu, Lin, and Jin

We present a tunneling study on single-crystalline parent-cuprate thin films, i.e., a series of Pr2CuO4±δ with tunable superconducting transition temperature. The zero-bias anomaly in the differential conductance, well-reported in the normal state of R2-xCexCuO4 (R = Pr, Nd, La) and named as normal-state gap (NSG), is observed in the Ce-free samples. This NSG behaves quite robustly against magnetic fields up to 16 T, but fades away with increasing temperature. Most importantly, we find that the magnitude of the NSG becomes larger with increasing point-contact junction resistance on the superconducting films, which is further enhanced in the nonsuperconducting samples with more oxygen disorder. The origination of NSG can be understood in the framework of the Altshuler-Aronov-Lee theory, where the disorder-induced electron-electron interactions suppress the density of states and thereby result in a soft Coulomb gap.