Dispersion and energy spectrum of spin excitations in an underdoped La_1.90Sr_0.10CuO_4

TL;DR

This study investigates spin excitations in underdoped La_1.90Sr_0.10CuO_4 using neutron scattering, revealing an hourglass dispersion pattern and a peak-dip-hump structure similar to optimally doped samples, with a lower crossover energy.

Contribution

It provides detailed measurements of spin excitation dispersion and energy spectrum in underdoped La_1.90Sr_0.10CuO_4, highlighting differences from optimally doped samples and discussing their implications.

Findings

Incommensurate peaks disperse inward with increasing energy.

A single peak appears at E_cross ~40 meV, merging the incommensurate peaks.

Hourglass-shaped dispersion and peak-dip-hump structure are observed.

Abstract

We performed inelastic neutron experiments on underdoped La_2-xSr_xCuO_4(x=0.10, T_c=28.6K) using a time-of-flight neutron scattering technique. Four incommensurate peaks on the two-dimensional reciprocal plane disperse inwards toward an antiferromagnetic zone center as the energy increases. These peaks merge into a single peak at an energy E_cross around w=40+-3meV. Beyond E_cross, the peak starts to broaden and ``hourglass-like'' excitations are observed. The E_cross in the underdoped sample is smaller than that reported for the optimally doped La_1.84Sr_0.16CuO_4. The reduction of the E_cross is explained by the doping-independent slope of the downward dispersion below the E_cross combined with the smaller incommensurability in the underdoped sample. In the energy spectrum of chi"(w), we observed a similar "peak-dip-hump" structure in the energy region of 10~45meV to that reported for the optimally doped sample. We discuss the relation between the hourglass-shaped dispersion and the peak-dip-hump energy spectrum.