Uncollapsed LaFe2As2 phase: Compensated, highly doped, electron-phonon-coupled, iron-based superconductor

Abstract

The recently discovered ${\mathrm{LaFe}}_{2}{\mathrm{As}}_{2}$ superconducting compound, member of the 122 family of iron pnictide superconductors, becomes superconducting below ${T}_{c}\ensuremath{\approx}13\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, 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 \ensuremath{\sim}0.42 electrons per unit cell just above ${T}_{\mathrm{c}}$, and high effective masses $\ensuremath{\sim}3{m}_{0}$. The temperature dependence of transport properties strongly resembles that of conventional superconductors, pointing to a key role of electron-phonon coupling. From this evidence, ${\mathrm{LaFe}}_{2}{\mathrm{As}}_{2}$ can be regarded as the connecting compound between unconventional and conventional superconductors.