Magnetization measurements under hydrostatic pressure up to 8 kbar in the pyrochlore superconductor ${\mathrm{R}\mathrm{b}\mathrm{O}\mathrm{s}}_2{\mathrm{O}}_6$ ($T_c\simeq 6.3\mathrm{K}$ at $p=0$) were carried out. A positive pressure effect on $T_c$ with $d{T}_c/dp=0.090(3)\mathrm{K}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$ was observed, whereas no pressure effect on the magnetic penetration depth $\lambda$ was detected. The pressure independent ratio $2{\Delta }_0/k_B{T}_c=3.72(2)$ (${\Delta }_0$ is the superconducting gap at zero temperature) was found to be close to the BCS value 3.52. Magnetization and muon-spin rotation measurements of $\lambda (T)$ indicate that ${\mathrm{R}\mathrm{b}\mathrm{O}\mathrm{s}}_2{\mathrm{O}}_6$ is an adiabatic $s$-wave BCS-type superconductor. The value of $\lambda$ extrapolated to zero temperature and ambient pressure was estimated to be 230(30) nm.

• Received 22 April 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.157004