Pressure-induced charge distribution effect on superconducting critical temperature of HgBa2Ca2Cu3O8+δ☆

Abstract According to the local density approximation for electronic structure calculations, the doping level of CuO 2 layer does increase under pressure by a relatively small amount, less than 0.02 additional holes per Cu atom at 9.2GPa. Thus, it seems necessary to consider mechanisms other than changes in doping level for the increase of T c under pressure. Based on the data obtained from the powder neutron diffraction experiments up to a pressure of 8.5GPa, we have calculated the valences of Cu and the pressure-induced change of the hole concentration in the inner and outer CuO 2 layers in Hg-1223 samples by using the method of Bond Valence Sums (BVS). The results are rather good and could provide a possible explanation for the large increase of superconducting critical temperature in this material under pressure.