Dynamical spin chirality and spin anisotropy inSr14Cu24O41: A neutron polarization analysis study

Abstract

Low-dimensional quantum spin systems constitute an ideal built-in laboratory to study fundamental aspects of solid-state physics. By engineering suitable compounds, fundamental theories have been tested during the past decades and many studies are still underway. Quantum phase transitions, possible coupling mechanisms to explain high-${T}_{C}$ superconductivity, ring exchange and orbital and spin currents, and the occurrence of Luttinger liquids and Bose-Einstein condensation are among the matters studied in this fascinating area of quantum systems. Here we add two values to this extensive list, which are the study of the spin anisotropy in spin-singlet ground-state compounds and the study of magnetic chirality, as measured by inelastic polarized neutron scattering techniques. To this end we have used the paramagnetic spin-singlet ground-state compound ${\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ and discussed in detail the scattering properties of the first excited state of the chain sublattice, a spin triplet. In-plane and out-of-plane magnetic fluctuations are measured to be anisotropic and further discussed in the light of the current hypothesis of spin-orbit coupling. We show that under appropriate conditions of magnetic field and neutron polarization, the trivial magnetic chirality selects only one of the Zeeman-split triplet states for scattering and erases the other one that possesses opposite helicity. Our analysis pertains to previous studies of dynamical magnetic chirality and chiral critical exponents, where the ground state is chiral itself, the so-called nontrivial dynamical magnetic chirality. As it turns out, both trivial and nontrivial dynamical magnetic chiralities have identical selection rules for inelastic polarized neutron scattering experiments and it is not at all evident that they can be distinguished in a paramagnetic compound.