Tunable Magnon Interactions in a Ferromagnetic Spin-1 Chain

Abstract

NiNb2O6 is an almost ideal realization of a 1D spin-1 ferromagnetic Heisenberg chain compound with weak unidirectional anisotropy. Using time-domain THz spectroscopy, we measure the lowenergy electrodynamic response of NiNb2O6 as a function of temperature and external magnetic field. At low temperatures, we find a magnon-like spin-excitation, which corresponds to the lowest energy excitation at q ∼ 0. At higher temperatures, we unexpectedly observe a temperaturedependent renormalization of the spin-excitation energy, which has a strong dependence on field direction. Using theoretical arguments, exact diagonalizations and finite temperature dynamical Lanczos calculations, we construct a picture of magnon-magnon interactions that naturally explains the observed renormalization. This unique scenario is a consequence of the spin-1 nature and has no analog in the more widely studied spin-1/2 systems. arXiv:1907.06542v1 [cond-mat.str-el]

Quantum Critical Magnetic Excitations in Spin-1/2 and Spin-1 Chain Systems

“…In the ab plane, the weakly coupled Ising chains sit on a triangular lattice, a prototypical motif for geometric frustration [21]. The magnetism in NiNb 2 O 6 is more isotropic, so that the exchange coupling can be described by a Heisenberg term, with an additional term for the uniaxial anisotropy [51,52]. Frustration has also been argued to manifest itself in NiNb 2 O 6 [51].…”

“…3 features (a) spin-1 operators S i instead of spin-1/2, (b) a more isotropic exchange term S i • S j , and (c) an additional term for the local onsite anisotropy D. While the TFIC model in Eq. 2 can be studied analytically, the Hamiltonian for NiNb 2 O 6 has been studied numerically by exact diagonalization and density matrix renormalization group methods [52]. Some 'in-between' situations of these two distinct models, including the Blume-Capel model, which deal with (a) and (c) but with an Ising exchange term and without the coupling to external field, can also be rigorously solved [69][70][71][72].…”

Persistence of Ising-like easy-axis spin correlations in the paramagnetic state of the spin-1 chain compound NiTe2O5

“…In the ferromagnetic (FM) case, conventional magnonlike spin flip constitutes the elementary excitation while quenching quantum fluctuations. The typical examples include Y 2 BaNiO 5 [19], Ni(C 2 H 8 N 2 ) 2 NO 2 (ClO 4 ) [20], and NiCl 2 -4SC(NH 2 ) 2 [21] for the AFM case, as well as NaCrGe 2 O 6 [22] and NiNb 2 O 6 [23] for the FM one. The latter FM chains adopt a FM ground state, while showing pronounced magnon-magnon interactions.…”

Persistence of Ising-like easy-axis spin correlations in the paramagnetic state of the spin-1 chain compound NiTe$_2$O$_5$

“…In the ferromagnetic (FM) case, conventional magnon-like spin flip constitutes the elementary excitation while quenching quantum fluctuations. The typical examples include Y 2 BaNiO 5 [19], [20], and NiCl 2 -4SC(NH 2 ) 2 [21] for the AFM case, as well as NaCrGe 2 O 6 [22] and NiNb 2 O 6 [23] for the FM one. The latter FM chains adopt a FM ground state, while showing pronounced magnon-magnon interactions.…”