実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report

課題番号 Project No.

装置責任者 Name of responsible person

2017A0013

Kenji Nakajima

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Spin dynamics in the quantum spin liquid state of CaCu3(OH)6Cl2

AMATERAS (BL14)

0.6H2O

実施日 Date of Experiment

実験責任者名 Name of principal investigator

2017/6/8 – 2017/6/12

Kazuki Iida所属 Affiliation
CROSS
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
Co-aligned single-crystal CaCu3(OD)6Cl2 0.6D2O.

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

Ground state of the spin-1/2 perfect kagome lattice is believed to be a quantum spin liquid (QSL). It isof great interest whether or not intrinsic spin gap exists in the QSL state [S. Yan et al., Science 332, 1173(2011)], which can provide us strong constrain to construct the QSL theory. So far, all reported spin-1/2
perfect kagome-lattice compounds have impurity (i.e., atomic site randomness between Cu2+ andnonmagnetic ions), which prevents us to investigate the existence of spin gap because impurity gives
rise to low-energy scattering [T.-H. Han et al., PRB 94, 201111 (2016).]. To discuss the spin gap problem
in the spin-1/2 kagome lattice, we performed single-crystal inelastic neutron scattering measurements on
newly discovered spin-1/2 kagome compound CaCu3(OH)6Cl2·0.6H2O using AMATERAS.
We prepared co-aligned deuterated single crystals [about 400 pieces, see Fig. 1(a)], which were wellaligned confirmed by the diffraction pattern: we can clearly see the six-fold symmetry as shown in Fig.
1(b). The mosaic of the co-aligned sample was 4.3° (FWHM). The sample holder was attached to the3He cryostat. Measurements were performed at 0.3 and 40 K. Set of Eis of 12.5, 5.2, and 2.9 meV wereselected. In this report, we only show the data with Ei = 12.5 meV.
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2. 実験方法及び結果（つづき） Experimental method and results (continued)
Figure 2(a) shows the constant energy
map in CaCu3(OD)6Cl2·0.6D2O at 0.3 K.
Interestingly, this constant energy map can be
reproduced

quantitatively

assuming

thesinglet-to-triplet excitations on the kagome
lattice (not shown). We also show thedispersion relation along H and HH as shownin Figs. 2(b) and 2(c). The broad continuum
excitation was observed. These two dispersion
relations are the direct evidence of thefractionalized

excitation,orthespinoncontinuum, in the spin-1/2 kagome lattice.

Fig. 1. (a) Co-aligned CaCu3(OD)6Cl2 0.6D2O. (b)Diffraction pattern at 0.3 K. L and ℏω were integrated
in [-0.7, 0.7] and [-0.1, 0.1] meV, respectively.

Thus, our observation elucidated that thefractionalized excitation really exists in the spin-1/2 kagome lattice in the absence of chemical disorder.
Furthermore, we have succeeded in observing the gapped magnetic excitation using lower Ei (notshown). Therefore, our single-crystal inelastic neutron scattering measurements show the gapped
fractionalized excitation in the QSL state in the spin-1/2 perfect kagome CaCu3(OH)6Cl2·0.6H2O.
Finally, we would like to thank our local contacts Dr. Kenji Nakajima and Dr. Seiko Ohira-Kawamura
for their nice support on the experiment. We also appreciate the staff of the MLF SE team.

Fig. 2. (a) Constant energy map in CaCu3(OD)6Cl2 0.6D2O at 0.3 K. L and ℏω were integrated in [-0.7, 0.7]
and [2.5, 5.5] meV. (b) Dispersion along (b) H and (c) HH. L was integrated in [-0.7, 0.7]. (b) HH was
integrated in [-0.1, 0.1], and (c) H was integrated in [0.4, 0.6], respectively.

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