  In the physics of condensed matter, quantum critical phenomena and
unconventional superconductivity are two major themes. In electron doped
cuprates, the low upper critical field allows one to study the putative QCP at
low temperature and to understand its connection to the long standing problem
of the origin of the high Tc superconductivity. Here we present measurements of
the low temperature normal state thermopower (S) of the electron-doped cuprate
superconductor La2-xCexCuO4 (LCCO) from x=0.11 to 0.19. We observe quantum
critical S divided by T versus ln(1/T) behavior over an unexpectedly wide
doping range x = 0.15 - 0.17 above the putative QCP (x=0.14) with a slope that
scales monotonically with the superconducting transition temperature. The
presence of quantum criticality over a wide doping range provides a new window
on the criticality. The thermopower behavior also suggests that the critical
fluctuations are linked with Tc. Above the superconductivity dome, at x=0.19, a
conventional Fermi liquid S proportional to T behavior is found for T less than
equal to 40 K.
