Pseudogap state in overdoped Bi₂Sr₂CaCu₂O_8+y

We use interlayer intrinsic tunneling resistivity to probe the pseudogap in Bi2Sr2CaCu2O8+y in magnetic fields up to 60 T. A map of the field-temperature (H-T) diagram of the pseudogap state reveals the pseudogap as a dominant feature up to very high levels of hole doping. The unconventionally large quantum fluctuation regime observed on the overdoped side is consistent with the pseudogap in the vortex cores. Unlike the characteristic fields of the superconducting state, the field that closes the pseudogap at low temperatures is temperature-independent. It is related to the pseudogap temperature T* through a simple Zeeman energy scale, pointing to the pseudogap controlled by the spin rather than the orbital degrees of freedom. © 2003 Elsevier Science B.V. All rights reserved.