  The iron-based pnictide LaFe2As2 is not superconducting as-synthesized, but
it becomes such below Tc around 12 K upon annealing, as a consequence of a
structural transition from a phase with collapsed tetragonal crystal structure
to an uncollapsed phase. In this work, we carry out specific heat, Raman
spectroscopy and normal state electric and thermoelectric transport
measurements in the collapsed and uncollapsed LaFe2As2 phases to gain insight
into the electron interactions and their possible role in the superconducting
pairing mechanism. Despite clear features of strong electron-phonon coupling
observed in both phases, neither the low energy phonon spectra nor the
electron-phonon coupling show significant differences between the two phases.
Conversely, the Sommerfield constants are significantly different in the two
phases, pointing to much higher electron correlation in the superconducting
uncollapsed phase and confirming theoretical studies.
