Uncollapsed LaFe2 As2 phase: Compensated, highly doped, electron-phonon-coupled, iron-based superconductor

The recently discovered LaFe2As2 superconducting compound, member of the 122 family of iron pnictide superconductors, becomes superconducting below TcGëê13K, yet its nominal doping apparently places it in the extreme overdoped limit, where superconductivity should be suppressed. In this work, we investigate the normal state of magneto- and thermoelectric transport and specific heat of this compound. The experimental data are consistent with the presence of highly compensated electron and hole bands, with Gê+0.42 electrons per unit cell just above Tc, and high effective masses Gê+3m0. The temperature dependence of transport properties strongly resembles that of conventional superconductors, pointing to a key role of electron-phonon coupling. From this evidence, LaFe2As2 can be regarded as the connecting compound between unconventional and conventional superconductors.