Extended Strange Metal Phase in Electron-Doped La2-x Ce x CuO4

Landau's Fermi liquid theory offers a profound understanding of conduction electrons in metals. However, many strongly correlated materials, including heavy-fermions, cuprates, iron-based superconductors, and nickelates, exhibit non-Fermi liquid (NFL) behavior. A hallmark is the strange metal state, characterized by linear-in-temperature resistivity and a linear-in-energy single-particle decay rate. Using angle-resolved photoemission spectroscopy measurements, we systematically investigate electron-doped cuprate La2-x Ce x CuO4 (LCCO) to explore the doping, momentum, and temperature dependence of the self-energy. We observe robust linear-in-energy single-particle scattering across almost the entire momentum space, persisting at high doping levels and temperatures. The extended strange metal behavior suggests a unified normal state, in contrast to an adjacent pseudogap regime in the hole-doped cuprates. This indicates that the physics of the strange metal may be key to high-T c superconductivity, making LCCO an ideal system for exploring quantum criticality and offering new insights into the microscopic mechanisms for high-T c superconductivity.