Pressure effect on theTcofHgBa2CuO4+δwith 0.07≤δ≤0.39

The superconducting transition temperature (${\mathit{T}}_{\mathit{c}}$) of ${\mathrm{HgBa}}_2$ ${\mathrm{CuO}}_{4+\mathrm{\delta }}$ (Hg 1:2:0:1) has been determined under pressures up to 1.7 GPa over a wide δ range. We found that the linear pressure effect on ${\mathit{T}}_{\mathit{c}}$ (${\mathit{dT}}_{\mathit{c}}$/dP) is constant at +2.0±0.1 K/GPa for δ${\mathit{T}}_{\mathit{c}}$ and the ‘‘boomerang path’’ previously reported. Comparison of the present observations for δn) dependence of ${\mathit{T}}_{\mathit{c}}$ suggests that the inverse parabolic ${\mathit{T}}_{\mathit{c}}$(n) relation is less universal than originally envisioned, and that the observed large ${\mathit{dT}}_{\mathit{c}}$/dP of optimally doped Hg 1:2:0:1 and other members of the homologous series is a result of the change of electron bands induced by pressure.