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Electronic structure of the candidate 2D Dirac semimetal SrMnSb2: a combined experimental and theoretical study
by S. V. Ramankutty, J. Henke, A. Schiphorst, R. Nutakki, S. Bron, G. Araizi-Kanoutas, S. K. Mishra, Lei Li, Y. K. Huang, T. K. Kim, M. Hoesch, C. Schlueter, T. -L. Lee, A. de Visser, Zhicheng Zhong, Jasper van Wezel, E. van Heumen, M. S. Golden
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|As Contributors:||Jans Henke · Shyama Varier Ramankutty · Jasper van Wezel|
|Arxiv Link:||http://arxiv.org/abs/1711.07165v2 (pdf)|
|Date submitted:||2017-11-27 01:00|
|Submitted by:||Ramankutty, Shyama Varier|
|Submitted to:||SciPost Physics|
SrMnSb$_2$ is suggested to be a magnetic topological semimetal. It contains square, 2D Sb planes with non-symmorphic crystal symmetries that could protect band crossings, offering the possibility of a quasi-2D, robust Dirac semi-metal in the form of a stable, bulk (3D) crystal. Here, we report a combined and comprehensive experimental and theoretical investigation of the electronic structure of SrMnSb$_2$, including the first ARPES data on this compound. SrMnSb$_2$ possesses a small Fermi surface originating from highly 2D, sharp and linearly dispersing bands (the Y-states) around the (0,$\pi$/a)-point in $k$-space. The ARPES Fermi surface agrees perfectly with that from bulk-sensitive Shubnikov de Haas data from the same crystals, proving the Y$-$states to be responsible for electrical conductivity in SrMnSb$_2$. DFT and tight binding (TB) methods are used to model the electronic states, and both show excellent agreement with the ARPES data. Despite the great promise of the latter, both theory approaches show the Y-states to be gapped above E$_F$, suggesting trivial topology. Subsequent analysis within both theory approaches shows the Berry phase to be zero, indicating the non-topological character of the transport in SrMnSb$_2$, a conclusion backed up by the analysis of the quantum oscillation data from our crystals.
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Anonymous Report 3 on 2018-1-8 (Invited Report)
- Cite as: Anonymous, Report on arXiv:1711.07165v2, delivered 2018-01-08, doi: 10.21468/SciPost.Report.317
1 - Previous reports, claiming topological states in SrMnSb2, are quite indirect [ref 15 in the manuscript]. The present manuscript present the first direct k- and energy- resolved band structure as extracted by ARPES.
2 - The authors combine theory and various experiments to prove that the states near to the EF in SrMnSb2 are topologically trivial, in disagreement with the previous study .
3 - The manuscript is well written, detailed and the results are of broad interest.
1 - Tight binding band TB structure deviations from experimental ARPES band dispersion are not negligible. So the claims on the Berry phase from TB being zero maybe not fully conclusive. However, the Landau level diagramme in Fig. 7 (b) shows that the experimental Berry phase is zero, in line with the same result from TB.
Overall I find the claim of zero berry phase convincing even if the TB model for the band structure is not perfect.
This manuscript presents a combined experimental and theoretical investigation of the electronic structure of
SrMnSb2. The main conclusion of the manuscript is that electronic states near the Y-point are gapped above EF, implying trivial topology. This result is in contrast with previous results which suggested that SrMnSb2 is a magnetic topological semimetal.
In general, I believe that the manuscript is well presented and the results are of broad interest.In particular, the authors present a very detailed and comprehensive study of SrMnSb2, with both theory and experiment supporting their claim of trivial states in this system.
For these reasons I believe that the manuscript meets the SciPost cryteria of impact and I suggest the publication in SciPost.
1 - In the abstract the authors state that the agreement with DFT and TB is excellent. While I agree that the agreement with DFT is excellent (Fig 6), I cannot say the same for the TB (Fig A1). Similarly, at the end of Appendix A the authors state that "Fig. A1 shows good agreement between the ARPES and TB constant energy contours."
I suggest that the authors soften these claims (something like "TB and ARPES are in qualitative agreement" should work).
Anonymous Report 2 on 2017-12-31 (Invited Report)
- Cite as: Anonymous, Report on arXiv:1711.07165v2, delivered 2017-12-31, doi: 10.21468/SciPost.Report.314
comprehensive experimental and theoretical work
manuscript is extremly long - could have been written more concisely
The authors present a combinded experimental and theoretical study on SrMnSb2. The data are interesting and the conclusions are solid. I recommend publication of this manuscript once the requested changes have been taken into account.
1) Emphasis on the major findings is necessary in the abstract
2) theoretical procedure - how are these assumptions justified: spin-orbit is included as a perturbation and the value of the magnetic moment?
3) Is the crystallograhic unit cell the chemical unit cell here?
4) page 10 (intermediate conlusion): add the arguments here. I suppose the authors do means that based on their observations so far, the systems seems to be gapless.
5) is there a beating pattern in the transport data, i.e. a second band? - please comment
Anonymous Report 1 on 2017-12-27 (Invited Report)
- Cite as: Anonymous, Report on arXiv:1711.07165v2, delivered 2017-12-27, doi: 10.21468/SciPost.Report.310
1- Provision of first ARPES data on SrMnSb2, a material which is currently in the focus of interest. The presented ARPES gives complementary information to existing, mostly magnetotransport literature and allows the authors to challenge recent claims that SrMnSb2 is a representative of a magnetic topological semimetal (J. Y. Liu et al., Nature Materials 2017).
2- The authors present high-field magnetotransport data on one and the same SrMnSb2 crystals studied also by ARPES. It allows a direct quantitative comparison of quantumtransport with the observed Fermi surface structure in ARPES data.
3 - By comparison of two theory approaches (Tight binding and ab intio DFT) the authors shed light on a possible correlation of topology and a time reversal symmetry breaking due to a canted antiferromagnetic state as suggested by J. Y. Liu et al., Nature Materials 2017.
iu et al., Nature Materials 2017.
1 - The referee believes that the author`s conclusion that bulk transport is governed by Y-states only leaves some questions unanswered.
2 - The discussion of the kz-dispersive behavior of states at the Gamma point remain undecisive regarding their dimensionality (2D vs bulk).
The manuscript shows experimental data and calculations of high significance on a very interesting topic. It is generally well written and evaluation/interpretation steps are easy to follow. Figures are well done.
Publication is highly recommended provided the following comments/questions are addressed:
1 - Possible band bending effects on the filling of 2D states vs bulk states: In the main text the authors comment that "no significant time effects" were observed on the time scale of days. Nevertheless, band bending effects can be instantly present after cleaving. In a second step, K evaporation can alter such band bending effects, and thus observed shifts in the Fermi level of Y states might not necessarily only due to the donor behavior of the alkali metal.
2 - The authors describe a cleaving plane within the Sr - Sb1 - Sr unit as "most likely", and comment that atomic distances in STM "match well" a Sb1 terminating plane. If the referee understands well, Sr termination is just as likely. Are there also areas visible in STM where the surface is Sr terminated? What influence would alternating cleaving areas have on the average ARPES, e.g. by local variations in band bending?
3 - The authors claim that the Fermi surface visible in ARPES data transport perfectly matches the frequency of SdH oscillations and "unambiguously link the Y-states to the conductivity". The referee agrees with the former statement but points out that it is not surprising that broadened states around the Gamma point most likely will not appear well defined in the FFT of the SdH data. It is thus not clear how much the states at Gamma will contribute . Their mobility may be low as the authors speculate but DOS at EF high.
Does the the hole carrier density and average slope in Fig.2(f) fit to transport through exclusively the Fermi surface given by Y-states?
4 - From the kz dispersion in the Y-T direction (Fig. 5) the authors follow that Y-states are of 2D character. At the same time - also from Fig. 5 - a 2D character of states at the Gamma point are claimed from cuts along T-Z and Gamma-Y directions. The latter argument is not clear to the referee maybe due to a lack of knowledge. Along the Gamma-Z direction a dispersion is clearly visible, which would speak against a 2D character?
5- Ref. stresses the fact that dHvA data is more reliable than SdH frequencies regarding the Fermi surface for 2D-like materials. For SrMnSb2 deviations between SdH and dHvA by 20% was observed. The authors could comment in the manuscript on the respective error margins in the parameter A in the Onsager Eq. when evaluating their SdH data.
6 - In the discussion of the ARPES data the authors comment on the presence of 90deg domains visible in ARPES. The expected influence of such domains on non-local average transport properties should be commented on, in particular on the relative orientation of canted AFM phases between domains. What is the length scale of such domains with respect to a phase coherence and Berry phase length scales?
1 - A comment/discussion of possible band bending effects on the filling of 2D states vs bulk states is necessary, referring to points 1 and 2 in the report above.
2 - The referee believes that in order to claim that transport is due to Y-states only, further evidence or explanation should be provided (see point 3 in the report above). Does the derived hole carrier density from the average Hall slope in Fig.2(f) fit to a DOS estimation solely from Y-states at the Fermi level?
If not, how much would possible transport contributions from Gamma states affect the Berry phase estimation from LLs?
3 - A possible 3D character of states at the Gamma point should be further addressed (see point 4 in the report above). Up to now a possible kz-dispersion of states at the Gamma point in Fig. 3(a) could not be excluded according to the author`s discussion. From the presented theory, the statement that Gamma states are of 2D type from Fig. 5 (e.g. along the Gamma-Z direction) is - at least to the referee`s perception - not obvious.
4 - The authors describe a cleaving plane within the Sr - Sb1 - Sr unit as "most likely", and comment that atomic distances in STM "match well" a Sb1 terminating plane. It has to be commented if Sr termination after cleaving is equally likely or even observed e.g. in STM (see point 2 in the report above).
5 - A discussion or short comment on the influence of domains in non-local average transport properties should be included (see point 6 in the report above). What is the relative orientation of canted AFM phases between such domains? What is their length scale with respect to phase coherence and Berry phase length scales?