Isotopic difference in the heteronuclear loss rate in a two-species surface trap

We have realized a two-species mirror-magneto-optical trap containing a mixture of $^{87}\mathrm{Rb}\phantom{\rule{0.3em}{0ex}}(^{85}\mathrm{Rb})$ and $^{133}\mathrm{Cs}$ atoms. Using this trap, we have measured the heteronuclear collisional loss rate ${\ensuremath{\beta}}_{\mathrm{Rb-Cs}}^{\ensuremath{'}}$ due to intraspecies cold collisions. We find a distinct difference in the magnitude and intensity dependence of ${\ensuremath{\beta}}_{\text{Rb-Cs}}^{\ensuremath{'}}$ for the two isotopes $^{87}\mathrm{Rb}$ and $^{85}\mathrm{Rb}$ which we attribute to the different ground-state hyperfine splitting energies of the two isotopes.