Total energy local density calculations of the effects of pressure on the HgBa2Can-1CunO2n+2+δ (n = 1,2,3) superconductors show that the compressibility is anisotropic. Estimates of the bond compressibilities show that the Cu-O(2) (apical) bond is extremely compressible, while the Hg-O(2) bond is the least compressible. A simple model is proposed to describe compressibilities of Hg-1212, Hg-1223 and Hg-1234 on the basis of results obtained for the infinite layer (Sr1-xCax)1-yCuO2 and Hg-1201 compounds. The energy location of the van Hove singularity (vHs) - important in several theories of high-Tc superconductivity - is found to move towards EF with pressure, thereby showing a correspondence between the number of holes (from dopants) needed to shift EF down to the vHs and the pressure needed to be applied to a fixed dopant material to achieve the best Tc. Some consequences for understanding the pressure effects on the Tc of the Hg superconductors and possible experiments are suggested.
ASJC Scopus subject areas
- Condensed Matter Physics