実験報告書様式（プロジェクト利用）
承認日 Date of Approval
2014/05/27
承認者 Approver
Ryoichi Kajimoto
提出日 Date of Report
2014/05/27

Experimental Report
実験課題番号 Project No.2013P0201

装置責任者 Name of Instrument scientist

実験課題名 Title of experiment

Ryoichi Kajimoto

Study of structure and electronic properties of functional

装置名 Name of Instrument/（BL No.）

materials at BL01

4SEASONS (BL01)

実験責任者名 Name of principal investigator

利用期間 Dates of experiments

Shuichi Wakimoto

2013/4/1 – 2014/3/31

所属 Affiliation
Japan Atomic Energy Agency

１．研究成果概要（試料の名称、組成、物理的・化学的性状を明記するとともに、実験方法、利用の結果得られた主なデータ、考察、結論、図表等を記述してください。
Outline of experimental results (experimental method and results should be reported including sample
information such as composition, physical and/or chemical characteristics.
Study of high-Tc cuprates
High-Tc cuprates show characteristic hour-glass shaped
magnetic excitation, which has been expected to beclosely related to the superconductivity.

Previous

neutronbyresults

measurements

ofLa2-xSrxCuO4

revealed

that(LSCO)

magneticTOF

dynamical

structure factor S(w) has two maxima at ~18 meV and ~50
meV [1].

There are phonon branches near 18 meV and,

therefore, it is possible that the crossing with phonons
results in enhancement of magnetic excitation at thisenergy if there is a coupling between magnons andphonons at the first maximum in S(w).

However previous

TOF experiments measures projected magnetic signals
on to the a*b*-plane by aligning the incident neutron
parallel to the c-axis.

This method misses detailed

information of coupling between phonons and magnons.
To test if there is such a coupling, we have carried out 4
dimensional mapping of S(Q,w) to see details of bothmagnons and phonons at different zones.
For these measurements, we used a chopper
spectrometer

4SEASONS

atMLF,measured S(Q,w) by rotating crystals.

J-PARC,andTwo compositions

Fig. 1 : K-Energy slice for x=0.30(upper) and x=0.08 (lower).

１．研究成果概要（つづき） Outline of experimental results (continued).
of LSCO, x=0.08 and 0.30, were measured.

Here, x=0.08

shows magnetic excitation, while x=0.30 shows no magnetic
excitation, so the x-0.30 sample is used to evaluate phonons(Fig. 1).

Note that in Fig. 1, the hour-glass shape does notappear due to the resolution.

We analyzed the magnetic

excitation in x=0.008 by subtracting the phonon backgroundestimated from the x=0.30 data.

We find that S(Q,w) of

x=0.08 indeed shows maximum at ~18 meV equally in
different zones with different L values (Fig. 2).

This result

implies the existence of magnon-phonon coupling.

We will

study temperature dependence and also non-doped La2CuO4

Fig. 2 : S(Q,w) at different zones.

to collect more experimental evidence of this coupling.

Vertical arrows indicate energies
where phonon branches locate.

Study of S=1 triangular lattice system
What kind of the ground state is observed in the S = 1 triangular lattice is still an interesting issue. Forinstance, NiGa2S4 undergoes a 60° short-range magnetic ordered ground state, while LiVO2 shows aso-called valence bond solid (VBS) ground state. Recently, our colleague reported that LiVS2, which islocated at the border between a metal and a correlated insulator, shows a first order transition from aparamagnetic metal to a VBS insulator at Tc = 305 K upon cooling. The presence of a VBS state in theclose vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of aVBS state. In addition, a pseudogap was also observed in the high temperature metallic phase ofLiVS2, which likely originates from the VBS fluctuation. On the other hand, however, it is not observed
the spin gap in the VBS state nor the pseudogap. Therefore, we have performed that the time-of-flightneutron scattering measurements on powder LiVS2 to investigate the origin of the VBS state in LiVS2 bymeasuring the entire magnetic excitations.
Inelastic neutron scattering measurements were performed using powder LiVS2, which was packed
into the aluminum sample can with an indium seal. Measurements were done at T = 7, 150, and 300 K.
Incident energy of neutrons was Ei = 308 meV with the Fermi chopper frequency fFermi = 300 Hz.
An inelastic peak was observed at ħω = 220 meV, which is very closed to the value expected fromthe NMR measurement. On the other hand, the peak intensity is enhanced at high temperature. Inaddition, observed Bragg peaks of the sample were very weak. Since the LiVS2 is air sensitive, weconclude that the quality of the present sample used for our measurement was not good. We are now
asking our colleague to make a new sample.

必要に応じて、A4 サイズの用紙に続きを記入して下さい。
Please use A4-size papers for further reporting, if necessary.