Electron spin resonance for the detection of long-range spin nematic order

Abstract

In this paper we propose that electron spin resonance (ESR) measurements enable us to detect the long-range spin nematic order. We show that the frequency of the paramagnetic resonance peak in the ESR spectrum is shifted by the ferroquadrupolar order parameter together with other quantities. The ferroquadrupolar order parameter is extractable from the angular dependence of the frequency shift. In contrast, the antiferroquadrupolar order parameter is usually invisible in the frequency shift. Instead, the long-range antiferroquadrupolar order yields a characteristic resonance peak in the ESR spectrum, which we call a magnon-pair resonance peak. This resonance corresponds to the excitation of the bound magnon pair at the wave vector $\mathbf{k}=0$. Reflecting the condensation of bound magnon pairs, the field dependence of the magnon-pair resonance frequency shows a singular upturn at the saturation field. Moreover, the intensity of the magnon-pair resonance peak shows a characteristic angular dependence and it vanishes when the magnetic field is parallel to one of the axes that diagonalize the weak anisotropic interactions. We confirm these general properties of the magnon-pair resonance peak in the spin nematic phase by studying an $S=1$ bilinear-biquadratic model on the square lattice in the linear flavor-wave approximation. In addition, we argue applications to the $S=1/2$ frustrated ferromagnets and also the $S=1/2$ orthogonal dimer spin system SrCu${}_2$(BO${}_3$)${}_2$, both of which are candidate materials of spin nematics. Our theory for the antiferroquadrupolar ordered phase is consistent with many features of the magnon-pair resonance peak experimentally observed in the low-magnetization regime of SrCu${}_2$(BO${}_3$)${}_2$.

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Cited by in corpus (11)

• Bose-Einstein condensation of a two-magnon bound state in a spin-one triangular lattice
• Two-photon driven magnon-pair resonance as a signature of spin-nematic order
• Magnetically hidden state on the ground floor of the magnetic Devil's staircase
• Spin nematics in frustrated spin-dimer systems with bilayer structure
• Field-induced spin nematic Tomonaga-Luttinger liquid of the $S=1/2$ spin ladder system with the anisotropic ferromagnetic rung interaction
• Anisotropy-induced soliton excitation in magnetized strong-rung spin ladders
• Finite temperature thermodynamic properties of the spin-1 nematics in an applied magnetic field
• Local dynamics and detection of topology in spin-1 chains
• Magnetic excitations and transport properties in frustrated ferromagnetic chain
• Spin pumping into quantum spin chains
• Impurity effects in one dimensional spin nematic liquid