Elementary excitations in spin-1/2 antiferromagnets on the triangular lattice

We discuss a spin-1/2 Heisenberg antiferromagnet on the triangular lattice using the recently proposed bond-operator technique (BOT). We use the variant of the BOT which takes into account all spin degrees of freedom in the magnetic unit cell containing three spins. Apart from conventional magnons known from the spin-wave theory (SWT), there are high-energy collective excitations in the BOT which are built from high-energy excitations of the magnetic unit cell. We also obtain another high-energy quasiparticle which has no counterpart not only in the SWT but also in the harmonic approximation of the BOT. All observed elementary excitations produce visible anomalies in dynamical spin correlators. We show that quantum fluctuations considerably change properties of conventional magnons predicted by the SWT. The effect of a small easy-plane anisotropy is discussed. The anomalous spin dynamics with multiple peaks in the dynamical structure factor is explained that was observed recently experimentally in Ba3CoSb2O9 and which the SWT could not describe even qualitatively.

Automated summary

In this study, a spin-1/2 Heisenberg antiferromagnet on the triangular lattice was discussed using the bond-operator technique (BOT). It was found that high-energy collective excitations and another high-energy quasiparticle exist in the system. Quantum fluctuations considerably alter the properties of conventional magnons, and the anomalous spin dynamics observed experimentally recently cannot be described by SWT.