The FFLO State and Charge Density Wave States in Organic Superconductors

We have strong evidence for inhomogeneous superconductivity (the FFLO state) in organic superconductors. Our data show high sensitivity of the Pauli paramagnetic limit (Clogston-Chandrasekhar limit) to impurities, in contrast to the FFLO-normal state phase line, which is robust to the addition of impurities. Using fits to specific heat data and the alpha-model we show how the FFLO state can be predicted and parameters such as spin-orbit coupling extracted from the data. We will discuss the FFLO phase diagram in view of the more general superconducting phase diagram for organic and unconventional superconductors where the superconducting state is found adjacent to an ordered insulating magnetic state as a function of carrier density. As an example, given the proximity to a charge density wave state (CDW), some organic conductors have a CDW coexisting with a metallic state at ambient pressure. We will discuss early results and proposed experiments to measure the q-vector of a CDW in organic conductors with x-rays. We will show that these experiments will help understand the FFLO state.