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論文

Magnetic excitation in the $$S$$=1/2 Ising-like antiferromagnetic chain CsCoCl$$_{3}$$ in longitudinal magnetic fields studied by high-field ESR measurements

木村 尚次郎*; 大西 弘明; 奥西 巧一*; 赤木 暢*; 鳴海 康雄*; 萩原 政幸*; 金道 浩一*; 菊池 彦光*

Journal of the Physical Society of Japan, 92(9), p.094701_1 - 094701_9, 2023/09

 被引用回数:0 パーセンタイル:0

High-field electron spin resonance (ESR) measurements were performed on the $$S$$=1/2 Ising-like antiferromagnetic chain CsCoCl$$_{3}$$ in the frequency range up to 4.4THz and magnetic fields for $$H parallel c$$ up to 53T. We observed softening of the spinon excitation, which drives the spin chain into the quantum critical state at the critical field $$H_{c}$$=33.0T. Above $$H_{c}$$, we observed the string excitation at the wave number $$q$$=$$pi$$, which is characteristic of the $$S$$=1/2 spin chain in the quantum critical state in the magnetic fields. We also observed a crossover of the string excitation to the magnon bound state above the saturation fields $$H_{s}$$=43.9T upon increasing the magnetic fields. Finally, we discuss how the string excitation and magnon bound state can be excited by the electric dipole transition due to spin quadrupolar resonance.

論文

Optical selection rules of the magnetic excitation in the $$S$$ = $$frac{1}{2}$$ one-dimensional Ising-like antiferromagnet BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$

木村 尚次郎*; 大西 弘明; 奥谷 顕*; 赤木 暢*; 鳴海 康雄*; 萩原 政幸*; 奥西 巧一*; 金道 浩一*; He, Z.*; 谷山 智康*; et al.

Physical Review B, 105(1), p.014417_1 - 014417_9, 2022/01

 被引用回数:2 パーセンタイル:37.1(Materials Science, Multidisciplinary)

In this study, we clarify the selection rules of optical transitions from the ground state to the magnetic excited states in the quasi-one-dimensional quantum Ising-like antiferromagnet BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ with spin $$S$$ = $$frac{1}{2}$$ using the high-field electron spin resonance measurement with illuminating polarized electromagnetic waves. We demonstrate that the unconventional magnetic excitation via the pair creation of quasipaticles at wave numbers $$q_{z}=pi/2$$ and $$pi$$ in the field-induced quantum critical state can couple with both oscillating magnetic and electric fields. Our density matrix renormalization group calculations indicate that the observed selection rules can be explained by two- and four-fold periodical spin interactions, originating from the screw chain structure in BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$, in addition to the magnetoelectric coupling between spins and electric dipoles.

論文

Spin excitations of the $$S$$=1/2 one-dimensional Ising-like antiferromagnet BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ in transverse magnetic fields

奥谷 顕*; 大西 弘明; 木村 尚次郎*; 竹内 徹也*; 木田 孝則*; 森 道康; 三宅 厚志*; 徳永 将史*; 金道 浩一*; 萩原 政幸*

Journal of the Physical Society of Japan, 90(4), p.044704_1 - 044704_9, 2021/04

 被引用回数:1 パーセンタイル:17.22(Physics, Multidisciplinary)

The high-field multifrequency electron spin resonance (ESR), the magnetization, and the specific heat of single crystals of BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ (a quasi-one-dimensional Ising-like antiferromagnet with $$S=1/2$$) were measured in two different transverse magnetic fields: $$H parallel [100]$$ and $$H parallel [110]$$. A softening of the lowest ESR mode was observed near the saturation field of the magnetization around 40 T in $$H parallel [110]$$, whereas it occurs around 10 T in $$H parallel [100]$$, far below the saturation field. These observations were reproduced by numerical calculations using the density-matrix renormalization group methods, including the staggered magnetic fields induced by a uniform external magnetic field and the interchain magnetic exchange interaction. We found that the directional dependence of the lowest mode originates mainly from the remarkable angular dependence of the induced magnetic field. The interchain interaction is also quantitatively important for reproducing the experimental results. The directional dependence of the lowest mode is demonstrated by the particle-hole excitation of spinons using the Jordan-Wigner transformation.

論文

Magnetic structure and dispersion relation of the $$S$$=1/2 quasi-one-dimensional Ising-like antiferromagnet BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ in a transverse magnetic field

松田 雅昌*; 大西 弘明; 奥谷 顕*; Ma, J.*; Agrawal, H.*; Hong, T.*; Pajerowski, D. M.*; Copley, J. R. D.*; 奥西 巧一*; 森 道康; et al.

Physical Review B, 96(2), p.024439_1 - 024439_8, 2017/07

 被引用回数:12 パーセンタイル:51.78(Materials Science, Multidisciplinary)

BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ consists of Co chains, in which Co$$^{2+}$$ ion carries a fictitious spin $$frac{1}{2}$$ with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$ in magnetic field perpendicular to the $$c$$ axis which is the chain direction. With applying magnetic field along the $$a$$ axis at 3.5 K, the antiferromagnetic order with the easy axis along the $$c$$ axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the $$b$$ axis. We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in magnetic field is reproduced by the theoretical calculation based on the spin $$frac{1}{2}$$ $$XXZ$$ antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.

論文

Magnons and electromagnons in a spin-lattice-coupled frustrated magnet CuFeO$$2$$ as seen via inelastic neutron scattering

中島 多朗*; 須能 梓*; 満田 節生*; 寺田 典樹*; 木村 尚次郎*; 金子 耕士; 山内 宏樹

Physical Review B, 84(18), p.184401_1 - 184401_7, 2011/11

 被引用回数:32 パーセンタイル:76.31(Materials Science, Multidisciplinary)

We have investigated spin-wave excitations in a four-sublattice (4SL) magnetic ground state of a frustrated magnet CuFeO$$_2$$, in which "electromagnon" excitation has been discovered by recent terahertz time-domain spectroscopy. We have performed high-energy-resolution inelastic neutron scattering measurements in the 4SL phase, resolving fine structures of the lower-energy spin-wave branch near the zone center. We have developed a model Hamiltonian to describe the spin-wave excitations. The determined Hamiltonian parameters have successfully reproduced the spin-wave dispersion relations and intensity maps obtained in the inelastic neutron scattering measurements. The results of the spin-wave analysis have also revealed physical pictures of the magnon and electromagnon modes in the 4SL phase, suggesting that collinear and noncollinear characters of the two spin-wave modes are the keys to understand the dynamical coupling between the spins and electric dipole moments in this system.

論文

Longitudinal spin density wave order in a quasi-1D Ising-like quantum antiferromagnet

木村 尚次郎*; 松田 雅昌; 益田 隆嗣*; 本堂 英*; 金子 耕士; 目時 直人; 萩原 政幸*; 竹内 徹也*; 奥西 巧一*; He, Z.*; et al.

Physical Review Letters, 101(20), p.207201_1 - 207201_4, 2008/11

 被引用回数:51 パーセンタイル:86.25(Physics, Multidisciplinary)

擬一次元イジング的量子反強磁性体BaCo$$_2$$V$$_2$$O$$_8$$の中性子回折実験を行い、磁場中で新しいタイプの非整合磁気秩序が現れることを観測した。この秩序は本質的に古典系で予想されるネール秩序とは異なり、量子スピン鎖特有の量子揺らぎに起因する。ギャップレス量子一次元系に特徴的な朝永-ラッティンジャー液体的性質が非整合磁気秩序を引き起こしている。

口頭

擬一次元イジング型反強磁性体BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$の横磁場中磁気励起のDMRGによる解析

大西 弘明; 森 道康; 奥谷 顕*; 木村 尚次郎*; 萩原 政幸*

no journal, , 

擬一次元イジング型反強磁性体BaCo$$_{2}$$V$$_{2}$$O$$_{8}$$の横磁場中の磁気励起スペクトルをDMRGで解析した。磁場を[110]方向にかけた場合は飽和磁場近傍まで反強磁性秩序が保たれるのに対して、[100]にかけた場合は反強磁性秩序が速やかに抑制されて磁場誘起相転移が生じることが知られている。そこでのESRや磁化等の測定、および計算との比較について、萩原氏が講演予定である。その連続講演として、数値計算と理論的側面の詳細を報告する。

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