Combined paramagnetic and diamagnetic response of YBa2Cu3O7

It has been predicted that the zero frequency density of states of YBCO in the superconducting phase can display interesting anisotropy effects when a magnetic field is applied parallel to the copper-oxide planes, due to the diamagnetic response of the quasiparticles. In this paper we incorporate pa ramagnetism into the theory and show that it lessens the anisotropy and can even eliminate it altogether. At the same time paramagnetism also changes the scaling with the square root of the magnetic field first deduced by Vol ovik leading to an experimentally testable prediction. We also map out the analytic structure of the zero frequency density of states as a function of the diamagnetic and paramagnetic energies. At certain critical magnetic fi eld values we predict kinks as we vary the magnetic field. However, these p robably lie beyond currently accessible field strengths.