Spin excitations coupled with lattice and charge dynamics in La$_{2-x}$Sr$_{x}$CuO$_4$

TL;DR

This study investigates spin excitations in La$_{2-x}$Sr$_{x}$CuO$_4$ using neutron scattering, revealing a peak in spin susceptibility linked to phonon interactions and carrier concentration, highlighting complex spin-charge-lattice interplay.

Contribution

It provides new insights into the coupling between spin excitations, phonons, and charge dynamics in LSCO, especially around the 16-19 meV energy range, and how this varies with doping.

Findings

Peak in spin susceptibility at 16-19 meV in superconducting LSCO

Absence of peak in insulating and overdoped samples

Correlation between peak intensity and carrier concentration

Abstract

Spin excitations of layered copper oxide show various characteristic features, depending on the carrier concentration. In this study, we conducted inelastic neutron scattering (INS) measurements on La$_{2-x}$Sr$_{x}$CuO$_4$ (LSCO), with $x$ = 0, 0.075, 0.18, and 0.30 and La$_{2-x}$Sr$_{x}$NiO$_4$ (LSNO) with 1/3, to clarify the origin of the intensity enhancement in the excitation spectrum of LSCO at the energy ($\omega$) of 16--19 meV [Phys. Rev. B {\bf 91}, 224404 (2015), {\it ibid}. {\bf 93}, 094416 (2016)]. We confirmed the presence of a peak-structure in the $\omega$-dependence of the local spin susceptibility $\chi''(\omega)$ of superconducting (SC) LSCO with a peak energy of 16--19 meV, where the spin excitations intersect optical phonon branches. A comparable peak-structure is not observed in the insulating La$_2$CuO$_4$, LSNO, and heavily overdoped LSCO with $x$ = 0.30. A dome-shaped $x$-dependence of the integrated intensity around the peak energies is revealed for SC phase by summarizing the present and previously reported results. Furthermore, our phonon calculation on LCO shows the existence of two optical branches at $\sim$19 meV that could stabilize stripe-alignment of carriers due to out-of-plane vibrations of Cu or O of the CuO$_2$ planes. These results indicate the interplay among spin, charge, and lattice dynamics and suggest that the intensity enhancement is associated with their composite excitations.