Search

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. [Copyright &y& Elsevier]

A dense sample of MgB2 (Tc=38.5 K) was synthesized under 200 MPa pressure using a novel hot isostatic pressing (HIPing) technique, and a high-purity single crystal of YBa2Cu3O7−δ (Tc=93.5 K) was grown in a home-made BaZrO3 crucible. Electric field vs current density (E–J) isotherms of the MgB2 and YBa2Cu3O7−δ high-temperature superconductors were measured and analyzed in terms of the critical scaling model. E–J isotherm sets were taken at fields ranging from 2 to 90 kOe. Scaling and resistivity data reveal a smooth transition from a vortex glass to a vortex liquid state for the bulk MgB2 sample and the existence of both a vortex lattice melting line and a vortex glass to vortex liquid line in the YBa2Cu3O7−δ single crystal. The critical scaling exponents for both systems are presented. A more complete (H–T) phase diagram, containing the upper critical field Hc2(T), the vortex-glass transition line Hg(T), and the magnetic irreversibility line Hirr(T) was established for bulk MgB2. [Copyright &y& Elsevier]

From the c-axis interlayer resistivity measurements in a field up to 60 T, we evaluate the pseudogap closing field Hpg at which the low-energy density of state is restored to its ungapped value. We find that Hpg becomes temperature independent at low temperatures, in contrast to the characteristic fields of the superconducting state. The Zeeman energy of Hpg is scaled by the pseudogap temperature, indicating a predominant role of spins over the orbital effects in the formation of the pseudogap. [Copyright &y& Elsevier]