Opening a nodal gap by fluctuating spin-density-wave in lightly doped La$_{2-x}$Sr$_x$CuO$_4$

TL;DR

This study shows that in lightly doped La$_{2-x}$Sr$_x$CuO$_4$, the nodal gap is caused by fluctuating spin-density-wave fluctuations rather than charge-density-wave order, highlighting the role of spin fluctuations in pseudogap formation.

Contribution

It provides direct experimental evidence linking fluctuating SDW to the nodal gap, with no detectable charge order contribution, in a cuprate near the antiferromagnetic phase boundary.

Findings

Fluctuating SDW exists in the sample at low doping levels.

The strongest SDW fluctuations diminish when the nodal gap opens.

No charge-density-wave signatures were observed in x-ray scattering.

Abstract

We investigate whether the spin or charge degrees of freedom are responsible for the nodal gap in underdoped cuprates by performing inelastic neutron scattering and x-ray diffraction measurements on La$_{2-x}$Sr$_x$CuO$_4$, which is on the edge of the antiferromagnetic phase. We found that fluctuating incommensurate spin-density-wave (SDW) with a the bottom part of an hourglass dispersion exists even in this magnetic sample. The strongest component of these fluctuations diminishes at the same temperature where the nodal gap opens. X-ray scattering measurements on the same crystal show no signature of charge-density-wave (CDW). Therefore, we suggest that the nodal gap in the electronic band of this cuprate opens due to fluctuating SDW with no contribution from CDW.