Tunneling measurements of the energy gap in ${\mathrm{Bi}}_4{\mathrm{Ca}}_3{\mathrm{Sr}}_3{\mathrm{Cu}}_4{\mathrm{O}}_{16+\delta }$

We have measured at 4.2 and 53 K the tunneling current-voltage ($I-V$) characteristics of the new high-$T_c$ superconductor ${\mathrm{Bi}}_4{\mathrm{Ca}}_3{\mathrm{Sr}}_3{\mathrm{Cu}}_4{\mathrm{O}}_{16+\delta }$ with $\delta =0.32\mathrm{}$, using a low-temperature scanning-tunneling microscope. We obtain gap values $\Delta$ ranging between 15 and 23 meV. This corresponds to $\frac{2\Delta }{K_B{T}_c}$ values between 4.5 and 6.5. These results are consistent with strong-coupling superconductivity. A study of the spatial dependence of $\Delta$ has been done at 4.2 K.