Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites

TL;DR

This study reveals a pseudogap state with nodal-antinodal dichotomy in a ferromagnetic manganite, challenging the idea that such features are exclusive to high-temperature superconductors and linked to superconductivity.

Contribution

It provides experimental evidence of a pseudogap with nodal-antinodal features in a non-superconducting ferromagnetic material, suggesting a broader origin of this phenomenon.

Findings

Pseudogap with nodal-antinodal dichotomy exists in manganite La1.2Sr1.8Mn2O7.

The pseudogap state is present in a ferromagnetic metallic ground state.

This challenges the link between pseudogap features and superconductivity.

Abstract

A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the "d-wave" symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction. Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite "Fermi arcs". This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity or by invoking orders which are natural competitors of d-wave superconductors. Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La1.2Sr1.8Mn2O7. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.