Hole-doping and magnetic-field effects on the pseudogap in Bi1.74Pb0.38Sr1.88CuO6+δ studied by the out-of-plane resistivity

Two kinds of pseudogap temperatures T∗ and T∗∗ are deduced from the out-of-plane resistivity of Bi1.74Pb0.38Sr1.88CuO6+δ in magnetic fields up to 27 T. The pseudogap formed at T∗ is independent of the magnetic field, while another pseudogap at T∗∗ is suppressed by the application of magnetic fields. Taking into account that hole-concentration and magnetic-field dependences of T∗∗ resemble those of the superconducting transition temperature Tc, the pseudogap temperature correlating to the superconducting gap is not T∗ but T∗∗.