Thermoelectric power as evidence for a Quantum Phase Transition in electron-doped cuprates Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ .

We report magnetic field driven normal state thermoelectric power (S) measurement in electron-doped cuprate system Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ as a function of doping (x from 0.11 to 0.19) down to 2K. Consistent with the normal state Hall effect$^{a}$, S in the underdoped region (0.11-0.15) is negative. S changes sign at certain temperatures in overdoped samples (0.16-0.18), which supports the picture of a spin density wave rearrangement of the Fermi surface$^{b}$. More significantly, both S and S/T at 2K (at 9T) increase dramatically from x=0.11 to 0.16, and then saturate in the overdoped region. This kink around x=0.16 is similar to the previous Hall effect result$^{a}$ in Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$. Our results are further evidence for antiferromagnetism to paramagnetism quantum phase transition in electron-doped cuprates. a. Y. Dagan et al, Physical Review Letters, 92 (16) 167001, 2004 b. A. Zimmers et al, Europhysics Letters 70 (2) 225, 2005