Superconductivity and electronic structure of KFe2As2, RbFe2As2, and CsFe2As2 probed by thermal expansion and magnetostriction at very low temperatures

This thesis compares the iron-based superconductors KFe2As2, RbFe2As2, and CsFe2As2 based on thermal expansion and magnetostriction measurements at temperatures between 50 mK and 4 K and in magnetic fields up to 14 T. The upper critical field is paramagnetically limited for magnetic fields applied parallel to the FeAs layers. Quantum oscillations of the magnetostriction yield extremal cross-sectional areas of the Fermi surface and effective quasiparticle masses, which are enhanced considerably.