フルヤ　シュンスケ   FURUYA Shunsuke   古谷　峻介    所属   埼玉医科大学  医学部 教養教育    職種   専任講師
論文種別	学術雑誌(原著)
言語種別	英語
査読の有無	査読あり
表題	Electron spin resonance for the detection of long-range spin nematic order
掲載誌名	正式名：PHYSICAL REVIEW B ISSNコード：2469-9950/2469-9969
出版社	AMER PHYSICAL SOC
巻・号・頁	97(10)
著者・共著者	Shunsuke C. Furuya,Tsutomu Momoi
発行年月	2018/03
概要	Spin nematic phase is a quantum magnetic phase characterized by a quadrupolar order parameter. Since the quadrupole operators are directly coupled to neither the magnetic field nor the neutron, currently, it is an important issue to develop a method for detecting the long-range spin nematic order. 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 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 SrCu2(BO3)(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 SrCu2(BO3)(2).
DOI	10.1103/PhysRevB.97.104411
arXiv ID	arXiv:1707.08784
PermalinkURL	http://arxiv.org/abs/1707.08784v2