実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF Experimental Report

提出日 Date of Report
9/ 4 /2014

課題番号 Project No.

装置責任者 Name of responsible person

2014A0217

HIGEMOTO Wataru

実験課題名 Title of experiment
Study of the time-reversal symmetry breaking and the penetrationdepth in the non-centrosymmetric superconductivity of LaNiC2

装置名 Name of Instrument/（BL No.）

実験責任者名 Name of principal investigator
KATANO Susumu

6/12/2014 - 6/13/2014

D1 port
実施日 Date of Experiment

所属 Affiliation
Saitama 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.
LaNiC2.

The crystal structure of this system lacks the centrosymmetry.

At low temperatures below 3 K, thesystem exhibits superconductivity, and from its unique structure this superconductivity is considered not to be asimple BCS type, but to be an unconventional one.

The samples used were polycrystals made with anargon-arc furnace and qualified well from X-ray diffraction, specific heat, magnetization, and resistivity.
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.

The zero-field muon spin relaxation rate of LaNiC2 was measured on the D1 machine using a liquid-He flow
type cryostat.

We expected to use a dilution refrigerator to measure the relaxation rate below down to a 100mK order in the superconducting state; however, with several reasons we could not use that refrigerator in thisexperiment.

Before the experiment, we expected that with the He flow type cryostat the sample temperature

could be cooled down to 2 K at least, which is below the superconducting temperature Tc. In a previous muon
experiments on this system the relaxation rate is shown to be changed below Tc, indicating that the system
exhibits spontaneous magnetization in the superconducting state.

This implies the breaking time-reversal

symmetry, which leads that the superconducting state of the system is an unconventional p-wave one. Using
our well qualified sample to clarify the characteristics of this superconducting state much more, the relaxation
rate was measured from low temperatures to room temperature.
The electron relaxation rate λ obtained in this experiment is shown in the figure below.

The relaxation rateincreases linearly with decreasing temperature, but below about 20 K that dramatically increases.

The rates

below 10 K, however, increase a little. The lowest temperature obtained in the experiment was 3 K with sometroubles occurred in the cryostat; thus the rate in the superconducting state could not be measured. Theexperiments indicate that the mechanism of the relaxation may change at around 20 K.
mechanism cannot be identified yet.
1However, at present its2. 実験方法及び結果（つづき） Experimental method and results (continued)
To determine the spin relaxation mechanism at the higher temperatures we need further experiments.
Furthermore, to clarify the superconducting mechanism of this system more extensive experiments on therelaxation rate in the superconducting state using a dilution refrigerator are indispensable.

Fig. The electron relaxation rate λ as a function of temperature.

2