A Discrepancy in Thermal Conductivity Measurement Data of Quantum Spin Liquid β′-EtMe3Sb[Pd(dmit)2]2 (dmit = 1,3-Dithiol-2-thione-4,5-dithiolate)
Round 1
Reviewer 1 Report
The judgement of quantum spin liquid state is an important and challenge topic, EtMe3Sb[Pd(dmit)2]2 as one of intensively studied candidate materials, their thermal conductivity k/T has finite value is considered to be an important experiment evidence. While, the recent two research groups argue that k/T is tiny at zero temperature. This present paper try to answer the above discrepancy. Based on the resistivity, C-NMR and structural characterizations under different cooling rate. The authors claim that there is not cooling rate/ thermal cycle dependence. This work is very useful for further evaluation on the thermal conductivity results as judgement on the QSL states. Two issues should be clarified before its publication 1) the details of electrical transport measurement should be provided, such as sample size, probe size. 2) in Fig. 5, what is the author's opinion on the data, is possible added the present crystal's data of thermal conductivity.Author Response
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Reviewer 2 Report
Review report on crystals-1527388
Reizo Kato at el. studied the effects of the cooling rate on electrical resistivity, (average) crystal structure, and 13C-NMR results of β'-EtMe3Sb[Pd(dmit)2]2 above 5 K, and found that they are unimportant. The relation between these properties and the thermal conductivity, as well as the temperature range problem, has been carefully discussed with an unbiased review in the last section. The manuscript has been well written, and thus I recommend the publication of this manuscript.
The following three minor comments are provided for the authors’ consideration:
- The first paragraph may be a little misleading. It has been well known that the (ideal) triangular-lattice (Heisenberg) antiferromagnet has the long-range Neel ordered ground state, instead of a quantum spin liquid phase.
- The inset presented in Figure 2 isn’t mentioned in the caption. Moreover, it is hard to see all the resistivity curves clearly in the main figure. I understand these data overlap, but there seem to be only two black curves in the present Figure 2.
- The resistivity of β'-EtMe3Sb[Pd(dmit)2]2 is too large to probe below 28 K according to Figure 2. Is it really feasible to monitor electrical resistivity during the thermal conductivity measurement below 1 K, as highlighted by the authors in the last sentence?
Author Response
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Reviewer 3 Report
The discrepancy in thermal conductivity measurement data of quantum spin liquid candidate EtMe3Sb[Pd(dmit)2]2 is a very important issue in the field of quantum magnetism. While Yamashita et al. pointed out the domain formation associated with the cation disorder or the micro cracks as an origin, which depends on cooling rate (Ref. [13, 16, 17] of this manuscript), they did not provide convincing experimental evidence.
In this manuscript, Kato et al. (which is the only source of all the EtMe3Sb[Pd(dmit)2]2 single crystals) did a very nice study of the effect of cooling rate on the physical properties of EtMe3Sb[Pd(dmit)2]2, including electrical resistivity, low-temperature crystal structure, and 13C-NMR. They cannot find any significant cooling rate dependence. In this context, Yamashita et al.'s explanation on the discrepancy cannot be accepted. They have to further clarify this important issue, since they cannot reproduce their large-kappa data in their 2010 Science paper.
This work is very important and the manuscript is well written. I would recommend the publication of this paper in Crystals.
Author Response
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Reviewer 4 Report
The manuscript by Kato et al. reports on the cooling rate dependence of resistivity, crystallographic structure and 13C-NMR of the dmit-based organic charge transfer salt that is considered as one of the rare candidate materials for the realization of the spin-liquid ground state. A very recent issue that was discussed controversially in a series of high-impact papers is the question whether this material shows a finite thermal conductivity in the zero temperature limit or not. It was recently suggested that the applied cooling rate might explain the discrepancy between the different experimental results.
In this context, the authors describe a carefully conducted series of experiments under different cooling conditions. Even though their results turn out to be a “negative” result, i.e. the absence of a cooling rate dependence, and are performed at fairly high temperatures (i.e. at 4 K) and thus do not provide new insight into the putative quantum spin liquid behavior, I still believe that the results are important enough to warrant publication in Crystals.
Before final judgement, I would like to ask the authors to address following aspects.
- It would be nice to see the NMR spectra presented in Fig. 4 NOT offset from each other – in this way differences in the fine structure of the spectra might become visible. On a first glance, it appears that present in the slow-cooled data at 300 ppm is absent/shifted to lower values. If this is the case, the authors should please include a discussion in the manuscript on these changes.
- For the resistivity data in Fig. 2, it would be nice if the authors could include the information in the figure caption whether the data was taken upon cooling or in the subsequent warming run.
- On page 7, line 187, the authors argue that “the smaller heat capacity provides more homogeneous temperature distribution, and thus it is less plausible that the cooling rate plays an important role.” This argument assumes that there is no underlying glassy behavior that could give rise to a cooling rate dependence. If the material e.g. was to be a spin glass, then also a low-temperature cooling rate dependence might be expected despite more homogeneous temperature conditions set by the cryostat environment.
- On page 2, line 45, the authors argue that “The thermal conductivity is free from the contribution from the rotation of the methyl (Me-) group that disturbs the heat capacity analysis”. It would be important to note at which temperature these contributions are expected and to provide a reference for this statement.
- In terms of the language, I would suggest small changes
- In the abstract, the word “negative” is not precise enough. The authors specify.
- Page 1, line 29, “belong to” should be replaced by “are”
Author Response
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