A semiconductor-like in-plane junction between overdoped and optimally doped La_2−xCe_xCuO₄

The electron-doped cuprate superconductor exhibits a unique electronic structure, where both electron and hole Fermi surface (FS) pockets coexist in the optimally doped (OP) region, while in the overdoped (OD) region there exists only a large hole FS pocket. It is therefore an intriguing question whether or not a p–n junction arises if the OD electron-doped cuprate interfaces with the OP compound. Here, we construct such an in-plane junction by selectively modulating the doping levels in thin films of La_2–xCe_xCuO₄ (LCCO) — a typical electron-doped cuprate. We find that the junction exhibits non-linear, asymmetric I–V characteristics, which are consistent with those of a p–n semiconductor junction, across a wide temperature range from 250 K to 10 K, regardless of the Hall coefficient sign change or the superconducting transition. We attribute these features to a potential barrier formed at the junction, which is set by the band bending in both OD and OP LCCO.