We have shown with ARPES that the electronic structure of the ferromagnetic metallic (FM) groundstate of the colossal magnetoresistive (CMR) bilayer manganite La1.2Sr1.8Mn2O7 (LSMO) shows striking similarities to that of the pseudogap phase in heavily underdoped cuprate high-Tc superconductors.
The FM phase is a polaronic metal, albeit with a strong anisotropic distribution of spectral weight in momentum space exhibiting a nodal–antinodal dichotomy. Quasiparticle excitations (QP) have been detected for the first time along the nodal direction (i.e. diagonal), and they are found to determine the metallic transport properties in the FM phase. Since this nodal-antinodal dichotomy in momentum space was so far considered a characteristically unique feature of the cuprates, these findings cast doubt on the assumption that the pseudogap state and the nodal-antinodal dichotomy in the cuprates are hallmarks of the superconductivity state. Furthermore, we found that the temperature dependent evolution of the nodal QP in LSMO tracks DC conductivity remarkably well, thus accounting for the macroscopic transport properties of LSMO.
Our results indicate that the microscopic mechanism leading to CMR in manganites is intrinsically a quantum phase transition that is kinetic energy-driven and linked to a crossover from a small polaron hopping regime in the paramagnetic state to a coherent polaronic conductor in the FM state.
- N. Mannella et al. Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites. Nature 438, 474 (2005)