STM/STS studies on the energy gap of Pb-substituted Bi₂Sr ₂CuO_6+δ in magnetic fields

The tunneling spectrum of high-Tc cuprates simultaneously exhibits kinks (or peaks) at low energy and peaks at high energy, suggesting the existence of two energy gaps. In order to clarify origins of these two gaps, we have performed the scanning tunneling microscopy/spectroscopy of the slightly overdoped Pb-substituted Bi₂Sr₂CuO_6+δ (Pb-Bi2201) (Tc∼20K) in magnetic fields. In zero field, almost all tunneling spectra exhibit clear peaks. In many cases, two peaks are simultaneously found around 10 mV and above 20 mV in each tunneling spectrum. By the application of the magnetic field of 7 T, peaks around 10 mV are strongly suppressed, but ones above 20 mV are not changed. The result indicates that peaks around 10 mV and above 20 mV possibly correspond to the superconducting gap and the pseudogap, respectively.