Peer review of: Strange semimetal dynamics in SrIrO3 (2020)


 REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author): Dear editor,
 The authors performed improvements to their manuscript. In addition, the authors have answered all
 my questions and taken my suggestions into account. I also noticed that all the points raised by the
 other referees have been treated fairly and seriously by the authors. In my opinion, the manuscript is
 now ready for publication.
Reviewer #2 (Remarks to the Author):
  The authors have improved the paper according to my comment and suggestions. Most of issues are
 properly addressed and the manuscript can be accepted for publication.
Reviewer #3 (Remarks to the Author):
  The authors have provided a detailed response to my questions raised in the first report, making their
 case stronger. Some parts of the manuscript have been improved still focusing of high quality Raman
 measurements of SrIrO3 films and the phenomenological interpretation of the experimental data.
 It seems to me that the weakest point of the manuscript is the lack of experimental confirmation of
 the low-temperature MFL regime. As clearly stated in the new version of the manuscript, “the MFL
 mass renormalization remains limited, and the log divergence of is not detectable”. Therefore, I am
 repeating my question about the energy scale D which might govern this MFL limit. What is the
 limiting D to finite values, since the MFL theory is introduced purely phenomenologically? Without any
 knowledge of D, the extensive usage of the MFL term, all over the manuscript, might be misleading for
 readers. It would be better to use terms like “MFL-like behavior“ or “linear T dependency”, etc.
 In the new version of the manuscript, the authors explain that “subtle structural differences between
 the polycrystalline materials and the thin films can yield different behavior at low temperatures
 (electronic structure reconstruction, location of the Dirac node, metal-to-insulator transition, sign of
 the magnetoresistance)”, and, in particular, that “slight changes in the lattice parameters can induce
 metal-to-insulator transition”. In other words, behavior of SrIrO3 systems may be quite dependent on
 details of the preparation and hence conductive properties may differ from a study to a study. This
 puts limitations on the generality of the results, which should be more clearly pointed out in the final
 version of the manuscript.
 Since the SrIrO3 systems are so sensitive to structural differences, I would not so easily exclude the
 possibility that lattice degrees of freedom play a role, as suggested by authors in their response. In
 the reference [Rev. Mod. Phys. 62 645], cited by the authors in their response to my comments, one
 finds that the ‘normal’ Bloch term involves “a linear variation of the resistivity with T, from the melting
 point down to below the Debye temperature Theta, and an ultimate T^5 variation for T < Theta /50”.
 That is, the T^5 behavior of the resistivity due to the scattering on phonons is limited to the very low
 temperatures, whereas the elevated temperatures are characterized by a linear dependence in T.
 Taking the value of Theta quoted by the authors, Theta = 800K, the T^5 behavior is observable below
 20K, which is irrelevant for the current study since it does not consider this low-temperature range at
 all.
 The Bloch-Gruneisen model [Rev. Mod. Phys. 62 645] has been derived for the scattering on acoustic
 phonons in a standard metal, assuming a single band and a large Fermi energy. If we listen to the
 authors, the system under investigation involves substantial electron correlations that certainly affect
 the electron-phonon interaction and, consequently, the scattering on phonons. Thus, the applicability
 of the simple Bloch-Gruneisen model in the case of SrIrO3 films is questionable. In order to discuss
 the origin of the scattering mechanisms, it might be better to consider the interplay between electron-
 electron and electron-phonon correlations. In any case, the importance of the scattering on acoustic
 phonons cannot be fully excluded, in addition to effects related to electron quasiparticle properties
 near the Fermi level. However, I can agree with the authors that “adding complexity to the analysis
 through additional e-ph terms in the memory function analysis” would not necessarily provide deeper
 understanding. I am just emphasizing that the origin of the scattering rate is not fully apparent from
 the data and that different scenarios can be put forward.
 In closing, the quality of the experimental research is apparently high. The SrIrO3 system is
 interesting and the current study should motivate further investigations that might give us answers on
 remaining open questions. However, the manuscript would strongly benefit from a more balanced
 discussion of the phenomenological results. The inclusion of the latter would make this work
 acceptable for publication in the Nature Communication.