Fluorinated Hg-1223 under pressure: the ultimate Tc of the cuprates?

High pressure experiments have revealed that Tc is affected by two main pressure-dependent parameters: the doping level of the CuO2 planes and by an intrinsic factor. The origin of the intrinsic factor is still unclear as, depending on the experiment, it is associated with the reduction of the c or the a lattice parameters. F incorporation into the Hg-1223 structure yields an enhancement of Tc up to a susceptibility onset of 138 K, mainly related to a compression of the a crystallographic axis. We have obtained a new high Tc record (166 K ± 1.5 K) by applying pressure (23 GPa) in the fluorinated Hg-1223 superconductor optimally doped. Tc increases with increasing pressure, reaching different maximum values, depending on the F doping level, and decreases for a further increase of pressure. This saturation of Tc may be the highest Tc that can be obtained for the cuprates, considering the particular structural characteristics of this system