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Transitions in Xenes between excitonic, topological and trivial insulator phases: influence of screening, band dispersion and external electric field

by Olivia Pulci, Paola Gori, Davide Grassano, Marco D'Alessandro, Friedhelm Bechstedt

This Submission thread is now published as

Submission summary

Authors (as registered SciPost users): Marco D'Alessandro
Submission information
Preprint Link:  (pdf)
Date accepted: 2023-05-22
Date submitted: 2023-04-28 16:35
Submitted by: D'Alessandro, Marco
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
  • Condensed Matter Physics - Theory
  • Condensed Matter Physics - Computational
Approaches: Theoretical, Computational


Using a variational approach, the binding energies $E_b$ of the lowest bound excitons in Xenes under varying electric field are investigated. The internal exciton motion is described both by Dirac electron dispersion and in effective-mass approximation, while the screened electron-hole attraction is modeled by a Rytova-Keldysh potential with a 2D electronic polarizability $\alpha_{2{\rm D}}$. The most important parameters as spin-orbit-induced gap $E_g$, Fermi velocity $v_F$ and $\alpha_{2{\rm D}}$ are taken from ab initio density functional theory calculations. In addition, $\alpha_{2{\rm D}}$ is approximated in two different ways. The relation of $E_b$ and $E_g$ is ruled by the screening. The existence of an excitonic insulator phase with $E_b>E_g$ sensitively depends on the chosen $\alpha_{2{\rm D}}$. The values of $E_g$ and $\alpha_{2{\rm D}}$ are strongly modified by a vertical external electric bias $U$, which defines a transition from the topological into a trivial insulator at $U=E_g/2$, with the exception of plumbene. Within the Dirac approximation, but also within the effective mass description of the kinetic energy, the treatment of screening dominates the appearance or non-appearance of an excitonic insulator phase. Gating does not change the results: the prediction done at zero electric field is confirmed when a vertical electric field is applied. Finally, Many-Body perturbation theory approaches based on the Green's function method, applied to stanene, confirm the absence of an excitonic insulator phase, thus validating our results obtained by ab initio modeling of $\alpha_{2{\rm D}}$.

Author comments upon resubmission

Hereby, we submit a revised version of the paper and we have already presented our detailed
response to the questions and criticisms raised by the referee. We believe that the present
version is suitable for publication in Scipost Physics

List of changes

1) In agreement with the suggestions of the referee we have improved the structure of the paper, the discussion of the results and the summary section in order to better clarify the physical content of the present analysis.

2) The physical meaning, advantages and limits of the various models discussed in the text are now better discussed
in the manuscript.

3) The section with the ab initio results has been improved and, in particular, the approaches used to
avoid the spurious interaction between stanene monolayers in neighboring supercell are now
discussed in more details. Also, new references on this aspect have been introduced.

4) We have corrected some typos in the text.

Published as SciPost Phys. 15, 025 (2023)

Reports on this Submission

Anonymous Report 1 on 2023-5-4 (Invited Report)


1) topic is important
2) approach is pertinent and (for the validation) state of the art


1) presentation could have been more accurate


In this revised submission, the authors meets the issues and points I raised in my report. Even though the paper has not really been restructured (as the authors claim) the corrections, extra sentences, more precise claims have improved the clarity of the article. As stated before, both the topic and the results obtained deserve publication. I can then confirm it here.

  • validity: high
  • significance: top
  • originality: high
  • clarity: ok
  • formatting: -
  • grammar: -

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