Phase diagram of cuprate superconductors at ultrahigh magnetic fields

Abstract

We have investigated the field-temperature (H − T ) diagram of the superconducting and pseudogapped states of Bi 2 Sr 2 CaCu 2 O 8+y over a wide range of hole doping (0.10 ≤ p ≤ 0.225). Using interlayer tunneling transport in magnetic fields up to 60 T to probe the density-of states (DOS) depletion at low excitation energies we mapped the pseudogap closing field H pg . We found that H pg and the pseudogap onset temperature T are related via a Zeeman relation gµBHpg ≈ kBT , irrespective of whether the magnetic field is applied along the c-axis or parallel to CuO 2 planes. In contrast to large anisotropy of the superconducting state, the field anisotropy of Hpg is due solely to the g-factor. Our findings indicate that the pseudogap is of singlet-spin origin, consistent with models based on doped Mott insulator.