Elucidation of Spin-Correlations, Fermi Surface and Pseudogap in a Copper Oxide Superconductor

Round 1

Reviewer 1 Report

This paper builds on previous work of some of the authors

and aims to extend the theory of Ref. 1 to the overdoped

regime. This so-called KS model divides the charge carriers in

KS and SS particles which are associated with the bonding and

antibonding states sketched in Fig. 1.

 

I found this manuscript rather confusing, regarding (a) presentation,

(b) terminology, and (c) content.

 

Concerning (a)

 

- In line 49 KS particles are introduced but they are only defined in line 87.

- Fig. 3 presents spin correlation length data from neutron scattering

  experiments but the meaning of the different symbols

  is not explained, neither in the caption nor in the text.

- The manuscript is full of typos, e.g. cupper (line 24), overdope (line 124),

  'vale' (line 93=) and many more, also in the references

  (e.g. 'stropeless' in line 338).

- In general, references should be corrected, e.g. Ref. 18 contains a

  wrong page number and Ref. 31  a typos in the name of the first editor

  (I'm sure there a much more)

 

Concerning (b)

 

- Authors discuss the vanishing of AF order at x=0.3 followed by

  the appearance of a spin glass phase (line 109). What usually is

  called AF, is the existence of a long-range ordered state which in

  cuprates exists below ~3% doping. The spin-glass phase is intermediate

  between the AF and SC but not beyond the SC dome. What authors call AF phase

  is the existence of dynamical AF spin correlations at intermediate energies.

  This confusion of static and dynamical order runs through the whole

  manuscript, e.g. in connection with the discussion of stripe order

  (lines 138 - 142). In LBCO the stripes are static while in LSCO there

  is a clear signature of dynamical stripe excitations, both from neutron

  scattering and from RIXS. Another example is line 171, where authors speak

  about localized spins in a region of the phase diagram where spins are

  clearly dynamic.

 

Concerning (c)

 

- The discussion of the pseudogap line T^*(x) is completely unfounded.

  Authors write that "both AF correlations and KS particles decrease

  together and finally disappear at T^*" whereas experimentally

  spin fluctuations are observed for doping p>p^*. Concerning the

  claim that KS particles vanish at T^* there is no evidence given

  in the manuscript.

 

- Line 212: '.. we call a new metallic phase beyond T^* "stange metallic

  phase" ....'. One of the hallmarks of the so-called strange metal phase

  in cuprates is the existence of non-saturating, linear-in-T resistivitiy.

  No evidence is presented, that the theory of the authors is compatible

  with this feature of a strange metal.

 

 

In view of the above I cannot recommend publication of the manuscript in

condensed matter.

Author Response

We deeply thank the referees for their useful report.
In attached document, we would like to reply to their comments and suggestions one by one.
Regarding the English of the manuscript, we asked an English Editing specialist to improve it.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript by Kamimura et al. presents a scenario for several of the key pieces of phenomenology of the cuprate superconductors. The framework is based on a two band model that includes on out-of-plane orbital, the Kamimura-Suwa model.  

 

I find that the paper gives a good overview of the theory and puts forth an overall sensible hypothesis. Nevertheless, there are some issues that I think needs to be addressed in final version of the paper. 

 

-Discussion around line 215: T^* is described as a phase transition where AF correlations vanish. This must be reformulated. There are always finite correlations, the question is how they depend on the distance (in the static case). If the spin-spin correlations is the OP the correlation length would diverge at the phase transition, clearly the correlation length never become 0. 

 

-In connection with Figure 4 and in section 4 it is argued that there are antinodal Fermi-pockets which are not visible in ARPES experiments because these are out of plane orbitals. Surely, ARPES is not the only probe that sees a pseudogap FS, there is STM, specific heat, etc. Would these also not observe the antinodal pockets? 

 

-Related to this, in connection with Fig 5b it is argued that the KS particles are gapped. I may misunderstand the presentation here, but is not argued to be related to the pseudogap? How is this consistent with the discussion above (Fig4/Section 4)?  

 

-In Figure 4. Why is the nodal pocket called a Fermi-arc? In other words, is there an explanation why the back side of the pocket is not seen? 

 

-Figure 5a. At 0 doping, surely it’s not a spin-glass phase, which would imply only short range correlations? It is antiferromagnetically ordered, with a finite transition temperature. 

 

-Fig 3. Is this a figure from one of the cited papers? It says “we performed…”. I think it should be made clear that this is a reproduction of previously published results. 

Author Response

We deeply thank the referees for their useful report.
In attached document, we would like to reply to their comments and suggestions one by one.
Regarding the English of the manuscript, we asked an English Editing specialist to improve it.

Author Response File: Author Response.pdf

Reviewer 3 Report

This work combines theoretical calculations and neutron inelastic scattering to elucidate the phase diagram of a copper superconductor, LSCO. The authors further explain why arpes cannot resolve the fermi pocekts predicted by theory. This work provides an approach to understand the phase diagram of LSCO including the pseudogap phase. The article is well-structured and results are sound. The manuscript is clearly written. appropriate references are also cited. Before this paper can be considered for publication, I would like the authors to address the following questions and comments.

1.     Overall there is not a section to explain the details of the experiment or calculations. For example, there is no details about the neutron scattering experiment (line 117). I would recommend the authors to add a method section at the end of the manuscript.

2.     Figure 3 is not very clear to me: what is the difference between green, black, red or blue dots? Why only some of them have error bars? There is also a black dot with a large error bar that looks like an outlier, which is very far away from the dotted thin line. Can authors try to explain this point?

3.     I would suggest authors to add color scale on figure 4. I believe figure 4 includes fermi surfaces from underdoped sample to overdoped sample. However, readers cannot tell which region is underdoped and which region is overdoped just from the figure. Adding a color scale would be helpful for readers.

4.     Line 182: authors argue that the mean free path of an ks particle makes it hard for arpes to resolve the fermi pockets. Since arpes is a surface sensitive probe with a very small probe depth (~1nm for VUV arpes), I am not sure why it is hard to resolve the fermi pockets if the mean free path is around 3nm?

Author Response

We deeply thank the referees for their useful report.
In attached document, we would like to reply to their comments and suggestions one by one.
Regarding the English of the manuscript, we asked an English Editing specialist to improve it.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

After rereading the revised manuscript and the comments

of the authors I have still some criticism concerning

this paper.

 

Line 215: Strange metallic phase: This term has been introduced

in Ref. 32, as correctly cited by the authors, however, is is by no means

clear why authors introduce this term on basis of the 'itinerant

behavior of SS particles'. As I wrote in my previous report

one of the hallmarks of the so-called strange metal phase

in cuprates is the existence of non-saturating, linear-in-T resistivitiy.

No evidence is presented, that the theory of the authors is compatible

with this feature of a strange metal.

Moreover, experimentally the strange metal phase has a fan-shaped

structure in the doping vs. temperature phase diagram and for

large doping is adjacent to the Fermi liquid phase.

In the phase diagram in Fig. 5 there is no border

to a Fermi liquid phase. Why?

 

Further points:

 

- Fig. 3: it should be scientific standard to attribute the different points

  to the different references. In the caption there are the three references

  22,23,24 but four different symbols (red, black, green circles and a triangle)

  in the plot.

 

Line 206, 207: There is a fragment of a sentence from the previous version.

 

I recommend that authors modify their manuscript according to these

points, especially with regard to the still unclear discussion of the

strange metal phase.

 

Author Response

We would like to thank the referee for his/her Comments. See the reply in attached document.

Author Response File: Author Response.docx

Reviewer 2 Report

To follow up my initial review I find that the authors have adequately addressed my previous concerns. I recommend that the paper be accepted for publication. 

Author Response

Thank you.

Reviewer 3 Report

I am now satisfied with the updated manuscript and can recommend it for publication.  

Author Response

Thank you.

Round 3

Reviewer 1 Report

I have looked at the revised version of the mentioned manuscript. Fig. 5 now contains in the top row two similar figures which differ by the labeling of the green region. Only the panel with the green region labeled ‚Unusual metal‘ should be kept.   Otherwise I recommend publication of the manuscript.