  In the high temperature cuprate superconductors, the pervasiveness of
anomalous electronic transport properties suggests that violation of
conventional Fermi liquid behavior is closely tied to superconductivity. In
other classes of unconventional superconductors, atypical transport is well
correlated with proximity to a quantum critical point, but the relative
importance of quantum criticality in the cuprates remains uncertain. Here we
identify quantum critical scaling in the electron-doped cuprate material
La2-xCexCuO4 with a line of quantum critical points that surrounds the
superconducting phase as a function of magnetic field and charge doping. This
zero-temperature phase boundary, which delineates a metallic Fermi liquid
regime from an extended non-Fermi liquid ground state, closely follows the
upper critical field of the overdoped superconducting phase and gives rise to
an expanse of distinct non Fermi liquid behavior at finite temperatures.
Together with signatures of two distinct flavors of quantum fluctuations, this
suggests that quantum criticality plays a significant role in shaping the
anomalous properties of the cuprate phase diagram.
