Transport properties of high-Tc mercury cuprates

Measurements of dc and ac susceptibility, resistivity, Hall effect, and thermoelectric power (TEP) on pure phase Hg‐1223 and mixed phase Hg‐1212–1223 cuprates are reported. The mixed phase compounds show the highest critical temperature (magnetic susceptibility onset of 138 K). Both Hall effect and TEP data support an underdoped state with hole‐like conduction. Oxygen annealing reduces the Hall coefficient (increasing the concentration of holes) and lowers the TEP (increasing the Fermi energy) features which can be explained by a simple Fermi‐gas picture. The Hall coefficient which increases linearly with temperature and the negative temperature coefficient of the TEP, however, cannot be explained by single‐band Fermi‐gas or ‐liquid theory, unless one introduces energy dependent carrier scattering. Estimates of the highest critical temperature based on the universality observed in the thermopower data for the cuprates suggest that 138 K is near the maximum one might expect for the Hg cuprates under optimal doping at atmospheric pressure.