Development of three-dimensional electronic structure via enhanced chain coupling in Pr-doped YBa₂Cu₃O₇

High-T_c cuprate superconductors undergo drastic property change upon Pr doping, including the resurrection of antiferromagnetism, the decimation of superconductivity, and more recently, the development of a 3D charge density wave (CDW) order. Previous results suggested a strong electronic structure modification on CuO₂ planes brought by their strong hybridization with 4f electrons from Y-site Pr. A more 3D low-energy electronic structure with considerable f orbital contents on portions of the Fermi surface have been predicted. Such hybridization provides a potential tuning knob of the electronic states in CuO₂ planes and, therefore, serves as a powerful handle to study intertwined orders. However, the hybridization itself and its consequences have been poorly examined experimentally. Here we performed angle-resolved photoemission spectroscopy measurements on Pr-doped YBa₂Cu₃O₇ at different Pr doping levels. Contrary to the conventional picture, traces of f electrons were absent in the low-energy electronic structure. A 3D electronic structure develops through enhanced chain coupling facilitated by Pr doping. Such change may promote the 3D CDW order recently observed. Our work exposed the importance of out-of-plane interaction in superconducting cuprates and shed light on the microscopic origin of the mysterious 3D CDW order. These results provided insights in understanding high-T_c superconductivity and paved a way for future precise-tuning studies of cuprates.