Vortex state and field-angle resolved specific heat oscillation for H ∥ ab in d-wave superconductors

When magnetic field is applied parallel to the ab-plane in d _x²-y²-wave superconductors, the transition of a stable vortex lattice structure, the spatial structure of local density of states, and the specific heat oscillation induced by rotation of the magnetic field orientation are investigated by quantitative calculations based on the self-consistent Eilenberger theory. We estimate how the vortex state changes depending on the relative angle between the node direction of the superconducting gap and magnetic field orientation. To reproduce the sign change of specific heat oscillation observed in CeCoIn₅, our study is perfomed by including a strong paramagnetic effect. The quantitative theoretical calculations give decisive information to analyze the experimental data on the field-angle dependence, and establish the angle-resolved specific heat experiment as a spectroscopic means to identify the node position of the superconducting gap.