  An understanding of the normal state in the high-temperature superconducting
cuprates is crucial to the ultimate understanding of the long-standing problem
of the origin of the superconductivity itself. This so-called strange metal
state is thought to be associated with a quantum critical point (QCP) hidden
beneath the superconductivity(1,2). In electron-doped cuprates in contrast to
hole-doped cuprates it is possible to access the normal state at very low
temperatures and low magnetic fields to study this putative QCP and to probe
the T~0 K state of these materials(3,4). We report measurements of the low
temperature normal state magnetoresistance (MR) of the n-type cuprate system
La2-xCexCuO4 (LCCO) and find that it is characterized by a linear-in-field
behavior, which follows a scaling relation with applied field and temperature,
for doping (x) above the putative QCP (x= 0.14)(5). This unconventional
behavior suggests that magnetic fields probe the same physics that gives rise
to the anomalous low-temperature linear-in-T resistivity(4). The magnitude of
the linear MR decreases as Tc decreases and goes to zero at the end of the
superconducting dome (x ~0.175) above which a conventional quadratic MR is
found. These results show that there is a strong correlation between the
quantum critical excitations of the strange metal state and the high-Tc
superconductivity.
