The spin nematic state in triangular antiferromagnets

Abstract

Motivated by the recently discovered triangular magnet NiGa 2 S 4 , we investigated a spin antiferronematic phase in the spin-1 bilinear-biquadratic model. We obtained the energy dispersion of elementary excitations by bosonizing spin operators, and the dynamic and static spin correlations are calculated. Low energy properties of NiGa 2 S 4 are consistently explained using the scenario of nematic order, including the algebraic temperature dependence of the specific heat C(T ) ∼ T 2 and a finite value of the magnetic susceptibility at zero temperature. We also calculated the rate of relaxation of the nuclear magnetic resonance, and found T −1 1 ∝ T 3 , a scaling different from that in the magnetically ordered phase. Some comments are also given on how to identify antiferronematic orders experimentally.

Unified spin model for magnetic excitations in iron chalcogenides

“…8. This fact is well known for the quadrupolar states [25,35,36] and is consistent with the absence of the magnetic Bragg peaks in the elastic neutron scattering in FeSe [12,13].…”

“…(1) is broken without breaking the time-reversal symmetry. The resulting Goldstone modes at q = 0 therefore have vanishing intensity (S(0,ω) ∝ ω [35,36]) in the static limit, consistent with the absence of Bragg peaks in FeSe under ambient pressure [12,13]. For small J 3 , close to the CAFM boundary, the spin-structure factor has pronounced minima at Q 1,2 = (π,0)/(0,π ) as can be seen in Fig.…”

“…In order to improve on the mean-field solution, we have performed a series of flavor-wave calculations, which accounts for the fluctuations in the spin-dipolar as well as spinquadrupolar channels [34][35][36][37]. The essence of this technique consists in expanding the local operators O i in terms of the three species (α,β = {0,1,2}) of bosons that transform in the fundamental representation of group SU(3):…”

Spin Ferroquadrupolar Order in the Nematic Phase of FeSe

“…However, there is no Bragg peak as the dynamical spin structure factor S (q, ω) shown in Fig. 3(b) has a vanishing spectral weight (∝ |q|) at q = 0, ω = 0 because of the conservation of time reversal symmetry in quadrupolar states [50,51,53,54]. In Fig.…”

“…The quadrupolar solution corresponds to the Bose-Einstein condensation of the appropriate boson (labeled b z ), and the remaining two flavors capture both spin and quadrupolar excitations [36,50,51]. Ex- …”