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

2017A0029

Kenji Nakajima

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Two-channel Kondo effect of PrT2X20 (T = transition metal

BL14 (AMATERAS)

elements, X = Al, Zn)

実施日 Date of Experiment

実験責任者名 Name of principal investigator

2017/4/17 – 2017/4/19

Kazuaki Iwasa
所属 Affiliation
Ibaraki University

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.
PrRu2Zn20 polycrystalline sample (2.9 g)

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.

We study f-electron states of intermetallic compounds, PrT2Zn20 (T = transition metals), which crystallize
into the Fd-3m cubic structure. These are attractive systems because of non-magnetic multipole ordering ofPr-ion f electrons and characteristic electric conductivities (T. Onimaru and H. Kusunose: JPSJ 85, 082002(2016)). PrIr2Zn20 exhibits a superconductivity below 0.05 K and a phase transition at 0.1 K. This phasetransition is attributed to a multipole ordering originating from the non-Kramers doublet ground state of thePr3+ f2 configuration (K. Iwasa et al.: PRB 95, 155106 (2017)).
In contrast, the isomorphic PrRu2Zn20 does not exhibit any phase transition. A previous
inelastic-neutron-scattering (INS) study did not resolve the crystal-electric-field (CEF) levels (K. Iwasa et al.:JPSJ 82, 043707 (2013)). The electron diffraction measurement has suggested a crystal-structuretransformation at 138 K (T. Onimaru et al.: J. Phys.: Condens. Matter 24, 294207 (2012)). Therefore, we carriedout an INS measurement for investigating magnetic excitation spectra of PrRu2Zn20 in the low-temperaturephase by using he high-resolution disk-chopper spectrometer AMATERAS (BL14).
2. 実験方法及び結果（つづき） Experimental method
1 and results (continued)

2. 実験方法及び結果（つづき） Experimental method and results (continued)
The polycrystalline sample was sealed inside an aluminum container. We use a GM cryostat with the basetemperature of 5 K. We adopted a multi-Ei mode with the incident neutron energy set of Ei = 2.24, 4.67, and15.13 meV. The pulse-shaping mode was used to obtain symmetric resolution functions.
Figure 1 shows magnetic excitation spectra of PrRu2Zn20 measured using Ei = 15.13 meV. The spectrum at
5 K is composed of excitation peaks at approximately 0.84, 1.97, 3.37, 3.96, 5.04, 5.82, 7.46, and 8.37 meV, asindicated by solid line for the fitted result. These sharp excitations depend on temperatures, and are attributed
to transitions between the CEF splitting of well-localized Pr-ion 4f2 electron configuration. The multi-peakstructure between 2 and 6 meV is observed more clearly, compared to the previous measurement. The sharp
peaks are suggestive of less hybridization effect between the f and conduction electrons. The spectrum 1t 150
K shown in the bottom part of Fig. 1 is thermally broadened, and it is difficult to identify the excitation levels.
Figure 2 shows results of low-energy spectra of PrRu2Zn20 by using Ei = 2.24 meV. The background
intensities exhibit monotonic increase with increasing energy. The spectrum is also contains many peaks at
approximately 0.490, 0.779, 1.047, 1.776 meV, as indicated by solid line for the fitted result. These also exhibit
temperature dependencies.
These experimental results indicate that the cubic symmetry at the Pr sites is broken on the structuraltransition at 138 K, because the present result is not consistent with an expected four CEF levels in theoriginal Fd-3m structure. Therefore, the degeneracy of the non-Kramers doublet ground state is lifted, whichmeans the 4f-electron multipole fluctuation is no longer active in the low-temperature region of PrRu2Zn20.
The crystal structure in the low-temperature phase is characterized by the wave vector q = (2/3, 2/3, 0) (T.
Onimaru et al.: J. Phys.: Condens. Matter 24, 294207 (2012)). Such long-period structure is expected tocontain different Wyckoff sites for the Pr ions, and the several individual CEF schemes appear below 138 K.
3530

2017.4.17
BL14@MLF
PrRu2Zn20(#7, #14)
25 Ei = 4.667 meV-1
Q = 1.0 – 2.0 Å

2017.4.17
BL14@MLF
PrRu2Zn20
30(#7, #14)
Ei = 15.126 meV-1
Q = 1.0 – 2.0 Å
255K

5K

Intensity (arb. units)

Intensity (arb. units)

202030 K
1550 K30 K1550 K
101080 K
80 K

55150 K
150 K

0-10-50

50-3.010

E (meV)-2.0-1.0

0.0

1.0

2.0

3.0

E (meV)

Fig. 1. INS spectra of PrRu2Zn20 measured

Fig. 1. INS spectra of PrRu2Zn20 measured

with Ei = 15.13 meV on BL14.

with Ei = 4.67 meV on BL14.

2