Pressure-Induced Hole Doping of the Hg-Based Cuprate Superconductors

We investigate the electronic structure and the hole content in the copper-oxygen planes of Hg-based high $T_c$ cuprates for one to four ${\mathrm{CuO}}_2$ layers and hydrostatic pressures up to 15 GPa. We find that with the pressure-induced additional number of holes of the order of $0.05e$ the density of states at the Fermi level changes by approximately a factor of 2. At the same time, the saddle point is moved to the Fermi level accompanied by an enhanced $k_z$ dispersion. This finding explains the pressure behavior of $T_c$ and leads to the conclusion that the applicability of the van Hove scenario is restricted. By comparison with experiment, we estimate the coupling constant to be of the order of 1, ruling out the weak coupling limit.

Figure 1

Number of pressure-induced holes (in units of electrons) for the Hg-based cuprates, Hg1201, Hg1212, Hg1223, and Hg1234 for pressures up to 15 GPa. The values are taken with respect to ambient pressure for each material. The solid circles correspond to the total number of holes created per unit cell, whereas the open symbols (triangles for the innermost layer and squares for the outer layers) reflect the situation in a particular layer. The symbols indicate the calculated data points, while the lines serve to guide the eye.

Figure 2

Band structure of Hg1201 along the high symmetry lines $\Gamma X$ and $ZR$ for different pressure values. The black, solid circles mark the calculated points, where the dotted lines serve to guide the eye. The Fermi level is set to zero and indicated by a horizontal line, and the energy is given in eV.

Figure 3

Densities of states $N$ in states per eV and unit cell of Hg1201, Hg1212, Hg1223, and Hg1234 for pressure values of 0, 5, 10, and 15 GPa.

Figure 4

Densities of states at the Fermi level $N_0$ in states per eV and unit cell in Hg1201, Hg1212, Hg1223, and Hg1234 for pressure values of 0, 5, 10, and 15 GPa.