Scanning Tunneling Spectroscopy of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CuO}}_{6+\delta }$: New Evidence for the Common Origin of the Pseudogap and Superconductivity

Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CuO}}_{6+\delta }$ between 275 mK and 82 K. Below $T_c=10\mathrm{K}$, the spectra show a gap with well-defined coherence peaks at $\pm {\Delta }_p\simeq 12\mathrm{meV}$, which disappear at $T_c$. Above $T_c$, the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at $T^{*}\simeq 68\mathrm{K}$. The comparison with ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin.