Neutron scattering study of spin ordering and stripe pinning in superconducting La$_{1.93}$Sr$_{0.07}$CuO$_4$

TL;DR

This neutron scattering study reveals the coexistence of spin stripe order, lattice fluctuations, and superconductivity in underdoped La$_{1.93}$Sr$_{0.07}$CuO$_4$, providing insights into intertwined electronic and structural orders.

Contribution

The paper uncovers strong lattice fluctuations and weak elastic magnetic order in underdoped cuprates, linking charge stripe order with lattice symmetry reduction and superconductivity.

Findings

Incommensurate spin fluctuations with no gap from 0.2 to 15 meV.

Weak elastic magnetic component appears below ~10 K.

Strong CuO$_6$ octahedra fluctuations and reduced lattice symmetry.

Abstract

The relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La$_{1.93}$Sr$_{0.07}$CuO$_4$, a superconductor with a transition temperature of $T_c = 20$~K. At $T\ll T_c$, we find incommensurate spin fluctuations with a quasielastic energy spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below $\sim10$~K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO$_6$ octahedra about Cu-O bonds, which are associated with inequivalent O sites within the CuO$_2$ planes. Furthermore, we observed a weak elastic $(3\bar{3}0)$ superlattice peak that implies a reduced lattice symmetry. The presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped \lsco. The coexistence of superconductivity with quasi-static spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.