Magnon Breakdown in a Two Dimensional Triangular Lattice Heisenberg Antiferromagnet of MultiferroicLuMnO3

Abstract

The breakdown of magnons, the quasiparticles of magnetic systems, has rarely been seen. By using an inelastic neutron scattering technique, we report the observation of spontaneous magnon decay in multiferroic LuMnO3, a simple two dimensional Heisenberg triangular lattice antiferromagnet, with large spin S=2. The origin of this rare phenomenon lies in the nonvanishing cubic interaction between magnons in the spin Hamiltonian arising from the noncollinear 120° spin structure. We observed all three key features of the nonlinear effects as theoretically predicted: a rotonlike minimum, a flat mode, and a linewidth broadening, in our inelastic neutron scattering measurements of single crystal LuMnO3. Our results show that quasiparticles in a system hitherto thought of as "classical" can indeed break down.

Electromagnon dispersion probed by inelastic X-ray scattering in LiCrO2

“…26) and LuMnO 3 (ref. 27). This points towards a general sensitivity of the magnon energy at the M -point to perturbations such as quantum fluctuations2829, further neighbour interactions or magnon–phonon coupling30.…”

“…These interactions are sensitive to the modulation of the bond length, similarly to other Cr 3+ compounds with short bonds such as ZnCr 2 O 4 (refs 15, 16) and MgCr 2 O 4 (ref. 17). Furthermore, LiCrO 2 shows a pronounced anomaly in the dielectric constant at T N but no ferroelectric polarization could be observed18 pointing towards an antiferroelectric ground state induced by the staggered chirality of the triangular layers1920.…”

Hybridization and Decay of Magnetic Excitations in Two-Dimensional Triangular Lattice Antiferromagnets

“…The observed renormalization value of the mode energies is found to be as much as about 40 %, which is much larger than in most classical spin systems covered in this review such as LuMnO 3 case (5 %). 16 Thus, it is very clear that there are strong quantum renormalization effects in this compound.…”

“…24,129 Except for the trimerization effect, RMnO 3 is a good real-world 2D TLAF manifestation for comparison with ideal 2D TLAF models. Importantly, the interplane exchange interaction between the Mn adjacent layers is smaller by two orders of magnitude compared with the inplane one, 16 which can be negligible for most of the cases. One more advantage of h-RMnO 3 , it is reasonably easy to grow high quality single crystals large enough for INS experiments.…”

“…These decay processes result in the enhanced linewidth of the magnon modes observed by experiments. 16 Inelastic neutron scattering (INS) is often an ideal probe for investigating the collective behavior of both magnons and phonons. [17][18][19][20] It allows for the direct comparison between experimental data and theoretical calculations of the dynamic spin-spin correlation function (or dynamical structure factor).…”