Planar Cu and O NMR and the Pseudogap of Cuprate Superconductors
Round 1
Reviewer 1 Report
In two recent publications the authors of the present paper revealed the opening of a temperature independent but doping dependent pseudogap at the Fermi surface, by analyzing NMR data from the planar oxygen sites from several publications. In this work they investigate how this spin susceptibility is related with the phenomenology of the planar Cu NMR data obtained from previous measurements. By comparing the two sets of data they conclude the apparent pseudogap dominates the planar Cu shifts, but there is a significant dependence on the direction of the applied magnetic field compared with the CuO2 planes. They attribute this Cu shift anisotropy to the existence of a second spin component. This is an interesting work that compiles data from so diverse sets of cuprate samples, and their arguments are well documented. I only suggest the authors to include if possible an analytic presentation of the samples presented in figures, since it would be better the work to stand by itself. Therefore, my suggestion is the paper to be published with this minor correction.
Author Response
Thank you for the positive response. As requested by the Reviewer, we added an Appendix with all information on the materials (samples, labels, and references).
Reviewer 2 Report
This work «Planar Cu and O NMR and the Pseudogap of Cuprate Superconductors.» is ready for publication.
The authors claim, a more coherent, unbiased assessment of all data, including planar Cu, is presented and consequences are discussed since the planar Cu data were collected and analyzed prior to the O data. The main finding is that the planar Cu shifts for one direction of the external magnetic field largely follow from the same states and pseudogap. This explains the shift suppression stated more recently, which leads to the failure of the Korringa relation in contrast to an enhancement of the relaxation due to antiferromagnetic spin fluctuations originally proposed. However, there is still the need for a second spin component that appears to be associated with the Cu 3d(x2−y2) hole to explain the complex Cu shift anisotropy and family dependence. Furthermore, it is argued that the planar Cu relaxation which was reported recently to be rather ubiquitous for the cuprates, must be related to this universal density of states and the second spin component, while not being affected by the simple pseudogap. Thus, while this universal metallic density of states with a pseudogap is also found in the planar Cu data, there is still need for a more elaborate scenario that eludes planar O.
The analysis of the work is qualitatively done. The conclusions are consistent with the goals set. Interesting work for readers of Condensed Matter.
Author Response
Thank you for the positive feedback. There were no requests.
Reviewer 3 Report
The manuscript "Planar Cu and O NMR and the pseudogap of cuprate superconductors", by Marija Avramovska, et al., seems to contain results that are interesting, timely, and sound enough to warrant publication. The text is well written and rather clear, the limitations and doubts are discussed in detail, the situation and the interpretation are far from being settled, but this corresponds to the state of the art about the nature and role of the pseudogap in cuprates. The question is open, the debate within the scientific community is ongoing, and I think that the present piece of work may trigger new theoretical and experimental investigation on this subject. I have no serious scientific concern about the content of the manuscript, and have a couple of suggestions to improve the presentation. Maybe this is a very speculative ground, but I think that the reader may benefit from a somewhat deeper discussion about the fate of a temperature-independent pseudogap when the temperature is raised, at least from the perspective of NMR data. As a minor point, in Eq. (15), when giving the approximate value for k1, the authors write both the \approx and the \gtrsim symbols in sequence, which makes no sense, this must be a typo.
Once the authors have taken into account my suggestions, I think that their manuscript may be accepted for publication in Condensed Matter.
Author Response
Thank you for pointing out the error in eq. 15.
We also added in Conclusions a sentence (in parentheses) about the temperature independence of the pseudogap. Thank you.
