On d-Wave Superconductors with a Zeeman or Exchange Splitting of the Spin-Up and --Down Fermi Surfaces

For a given Zeeman (or exchange) energy $h$, we used the Fermi-surface splitting, $\delta $\textit{$\mu $}, as a variational parameter, and showed: (1) For an s-wave superconductor, the Sarma state is actually an \underline {unstable} equilibrium state, which is known to exist for 0.5$