REVIEW 3 major objections 5 minor 56 references
An investigation of the two-dimensional non-Hermitian Su-Schrieffer-Heeger Model
T0 review · 3 major / 5 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read A two-dimensional non-Hermitian SSH model with staggered hopping develops nonzero Berry curvature and a finite anomalous Nernst conductivity, even though its Chern number is not quantized.
desk verdict The EP/Zak/circuit sections are mostly checkable and not worthless, but the central QANE claim in Section 4 contradicts the paper's own TRS statement: at gamma=0 the Chern number and Nernst conductivity must vanish, yet the paper reports C=-2.32 and finite alpha_xy. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the four-band reciprocal-space Hamiltonian $H_{\mathrm{NH,2D}}(k_x,k_y)$ in Eq. (5), a $4\times4$ matrix with alternating imaginary on-site potentials $i\gamma$ and $-i\gamma$ and hoppings $u,t_1$ along $x$ and $v,t_2$ along $y$. The argument runs through the biorthogonal left and right eigenvectors of this matrix: Eq. (17) defines the Berry curvature $\Omega^z_{\alpha}(k_x,k_y)$ from those eigenvectors, and Eq. (18) converts it into the anomalous Nernst conductivity via the Mott relation. Staggered hoppings make the inversion-symmetry condition $u=t_1$, $v=t_2$ fail, which is what allows the curvature to be nonzero; the rank-nullity theorem and the phase-rigidity factor $P_j$ are the tools used to identify genuine exceptional points, and the Wilson-loop formula in Eq. (11) gives the vectorized Zak phase.
What would settle it
For the Hermitian limit $\gamma=0$ with real staggered hoppings, compute the anomalous Nernst conductivity using the standard gauge-invariant Berry curvature of a Hermitian band structure. Time-reversal symmetry makes the curvature odd in $k$, so the integral in Eq. (18) must give zero; if the paper's right-right curvature gives a nonzero value in the same limit, the finite-Nernst conclusion is a convention artifact.
Extended reading notes
Core claim
The central claim is that, for the reciprocal-space Hamiltonian in Eq. (5), staggered hopping amplitudes $u \neq t_1$ and/or $v \neq t_2$ break inversion symmetry and, together with imaginary staggered potentials $\pm i\gamma$ that break time-reversal symmetry, produce a nonzero Berry curvature in certain parameter windows. Inserting that curvature into the low-temperature Mott formula for the anomalous Nernst conductivity gives a finite $\alpha_{xy}$, even though the Brillouin-zone integral of the right-right Berry curvature does not quantize to an integer. The paper therefore concludes that the quantum anomalous Nernst effect is possible for this system while the quantum anomalous Hall effect with integer Chern number is not. It also reports that tuning the gain/loss parameter $\gamma$ can drive the system between insulating and conducting regimes, and that true exceptional points can be located where coalescing eigenvalues coincide with the rank-nullity condition and vanishing phase rigidity.
Load-bearing premise
The whole finite-Nernst result rests on treating the right-right Berry curvature in Eq. (17) as a legitimate gauge-invariant Berry curvature whose integral can be fed into the Mott formula; the paper does not prove this invariance.
Editorial extensions
If this is right
- A temperature gradient applied to a 2D non-Hermitian SSH lattice with staggered hoppings should produce a transverse charge current, a measurable Nernst signal, without spin-orbit coupling.
- Because the Chern number is non-integer, the system will not show a quantized anomalous Hall conductance, but the Nernst response can still be substantial; the two effects are decoupled.
- By decreasing $\gamma$, the same Hamiltonian crosses from gapped (insulating) to gapless (conducting) behavior, so gain/loss strength acts as a switch for transport.
- In an RLC-circuit realization with the circuit Laplacian of Eq. (13), the topological boundary resonance condition is met for $R \leq 1\,\Omega$, and the integrated imaginary Berry phase gives a positive quantum Hall susceptance, indicating capacitive response.
Reading between the lines
- Editorial inference: the finite-Nernst claim depends on which of the four non-Hermitian Berry curvatures is inserted into Eq. (18); the paper uses the right-right curvature, but a gauge-invariant combination could give a different, possibly vanishing, transverse response.
- Editorial inference: for $\gamma=0$ with real hoppings, time-reversal symmetry is restored, and the standard Hermitian Berry curvature is odd over the Brillouin zone, so the integrated Nernst coefficient in Eq. (18) should vanish; a nonzero result at $\gamma=0$ would be a test of the curvature convention rather than a physical effect.
- Editorial inference: the same lattice, realized as an RLC circuit, could provide a direct experimental search: measuring the transverse voltage under a thermal gradient in a circuit version of Eq. (13) would check the predicted finite Nernst response at low resistance.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript studies a two-dimensional four-site non-Hermitian SSH model with balanced imaginary on-site potentials, deriving its energy spectrum, exceptional-point structure, vectorized Zak phase, and an RLC circuit analogue. The central transport claim appears in Section 4: for staggered hopping amplitudes with gamma = 0 (broken inversion symmetry but respected time-reversal symmetry), the authors report a nonzero Berry curvature, an unquantized Chern number C approx -2.32, and a finite anomalous Nernst conductivity computed from Eq. (18). The paper concludes that the model supports a quantum anomalous Nernst effect without spin-orbit coupling, despite the absence of Chern-number quantization.
Significance. If the central claim were correct, a finite transverse thermoelectric response in a spinless, time-reversal-invariant Hermitian limit would be a striking result requiring new physics beyond conventional Berry-curvature transport. The manuscript also contains checkable computations: the spectrum is given explicitly, the exceptional-point analysis is based on a discriminant and phase-rigidity criterion, and the Chern-number calculation is checked with the Fukui-Hatsugai-Suzuki method. These are strengths: the authors compute directly from the Hamiltonian rather than fitting to a target outcome. However, the central transport claim is internally inconsistent with the model's symmetries, and the nonquantized Chern number reported for a Hermitian TRS-invariant system indicates that the object being integrated is not the gauge-invariant Berry curvature. The manuscript's contribution is therefore dominated by the EP, Zak-phase, and circuit analyses, while the QANE claim, which is highlighted in the abstract and conclusion, does not survive scrutiny.
major comments (3)
- [Section 4, Eq. (18), Fig. 6(a),(b),(f)] The load-bearing claim of finite anomalous Nernst conductivity at gamma = 0 is internally inconsistent. For the parameter values of Fig. 6(a),(b), the paper states that TRS is respected (the Hamiltonian (5) is Hermitian with real hoppings, so H(-k)=H*(k) with T = I4 K). For a spinless TRS-invariant Bloch Hamiltonian, the Berry curvature of each band is odd, Omega_n(-k) = -Omega_n(k), so the BZ integral in Eq. (18) vanishes identically for every chemical potential, as does any Chern number. Reporting C = -2.3235 and a finite alpha_xy at gamma = 0 is therefore a contradiction. The statement that the four left/right curvature prescriptions yield the same Chern number cannot repair this, because in the Hermitian limit all prescriptions coincide with the conventional curvature. The non-integer C is a diagnostic that the Omega^RR used in Eq. (17) is not the physical, gauge-invariant Berry curvature, so the QANE conclusion in Section 4 and the abstract does not follow.
- [Section 2, paragraph following Eq. (8)] The rank-nullity statement is incorrect: the text reads 'nullity(matrix) = rank(matrix) + number of columns of the matrix', but the rank-nullity theorem gives nullity = number of columns - rank. The subsequent claim that GM < AM for the exceptional points relies on this relation, and as written it would produce impossible values (for a 4x4 matrix with rank 3 it would give nullity 7). This needs to be corrected for the EP identification argument to be valid.
- [Section 4, Eqs. (17) and (18), and FHS paragraph] The manuscript never establishes that the right-right Berry curvature used in Eq. (17) is gauge-invariant under the biorthogonal normalization, and the assertion that the four curvatures 'ultimately yield the same Chern number' is cited to Ref. [52] without verifying its assumptions for the present model with complex eigenvalues and band degeneracies. This is load-bearing because the paper interprets the nonquantized value C approx -2.32 as physical evidence of a nonzero Chern number and hence a finite Nernst response. A nonquantized integral of a non-gauge-invariant object has no topological or transport meaning; the FHS cross-check does not resolve this because the same non-Hermitian eigenvector gauge issues enter the link variables. A correct treatment of the gamma = 0 limit would give C = 0 and alpha_xy = 0, and any finite alpha_xy for gamma != 0 must come from a separately justified, gauge-invariant non-Hermitian curvature formula.
minor comments (5)
- [Section 3, Eq. (11b)] The citation 'refs. [66]' does not exist in the reference list; the reference numbering should be checked throughout.
- [References] The reference list jumps from [21] to [24] with no entries [22] and [23].
- [Section 4, Eq. (18)] The formula for alpha_xy is typeset in a garbled way: the prefactor and the integral measure are unclear, and the entropy-density expression is written without clear bracketing. Please rewrite Eq. (18) and the neighboring definitions with explicit variables and limits.
- [Figure 2 caption] The caption states 'Here the symbol g is the shortform of gamma' in the middle of a scientific caption; this informal notation should be removed and the axes labeled consistently.
- [Section 5] The statement that the quantum Hall susceptance is positive and 'indicative of capacitive properties' should be justified by showing how the imaginary Berry phase integral maps to the circuit susceptance; as written, the connection is asserted rather than derived.
Circularity Check
No circularity found: all claimed results are direct computations from the model Hamiltonian and standard transport/topological formulas.
full rationale
The paper's main claims are obtained by explicit calculation from the reciprocal-space Hamiltonian in Eq. (5). The Berry curvature in Eq. (17) is evaluated from the model's eigenvectors, the anomalous Nernst conductivity in Eq. (18) is the standard Mott-relation integral of that curvature, and the Chern number is computed both by direct integration and by the Fukui-Hatsugai-Suzuki lattice method. No parameter is fitted to reproduce the claimed Nernst conductivity or Chern number, and no target observable is used to define the model. The vectorized Zak phase and circuit Laplacian results are likewise direct numerical evaluations. The paper contains no load-bearing self-citation: the symmetry statements and formulas cite standard external references, and the authors' own prior work is not used to justify the central claims. A reader may dispute the validity of the Berry-curvature convention or the consistency of a finite Nernst response with TRS in the gamma = 0 Hermitian limit, but that is a physical-correction issue, not a circular-derivation issue, because the claimed output is not assumed in the input. The paper even acknowledges the non-quantization limitation explicitly, which further indicates that the result was not imposed. Therefore the circularity score is 0.
Assumptions & free parameters
free parameters (7)
- u =
1 (energy unit)
- t1 =
0.80, 0.95, 0.85, 1 in different figures
- v =
0.60, 0.23, 0.35, 0.41, 0.71 in different figures
- t2 =
0.75, 0.50, 0.71, 0.78 in different figures
- gamma =
0, 0.5, 0.59, 0.75, 0.77, 0.18 in different figures
- mu =
0
- Circuit parameters R, L1=L2, C, omega =
R=1,26,50 Ohm; L=0.1 mH or 10 mH; C=0.01 microF; omega near 3e4 s^-1
assumptions (7)
- standard math Rank-nullity theorem and discriminant criterion for eigenvalue coalescence
- standard math Wilson loop / discrete Zak phase formula
- standard math Kubo formula / quantum geometric tensor for Berry curvature and Mott relation for Nernst conductivity
- domain assumption Spinless time-reversal symmetry is represented by T = I4 K
- domain assumption Phase rigidity approaching zero identifies true exceptional points
- domain assumption The RLC circuit Laplacian is a faithful analog of the tight-binding Hamiltonian
- ad hoc to paper All four left/right combinations of Berry curvature yield the same Chern number, so the RR curvature can be used
Cite this review
Pith. "Pith review of An investigation of the two-dimensional non-Hermitian Su-Schrieffer-Heeger Model." pith.science (2026). https://pith.science/paper/A4Z5SCDN
@misc{pith2026250616867,
author = {Pith},
title = {Pith review of: An investigation of the two-dimensional non-Hermitian Su-Schrieffer-Heeger Model},
year = {2026},
howpublished = {\url{https://pith.science/paper/A4Z5SCDN}},
note = {Machine review of arXiv:2506.16867}
}
read the original abstract
This communication presents an examination of a two-dimensional, non-Hermitian Su -Schrieffer-Heeger (SSH) model, which is differentiated from its conventional Hermitian counterpart by incorporating gain and/or loss terms, mathematically represented by imaginary on-site potentials. The time-reversal symmetry is disrupted due to these on-site potentials. Exceptional points in a non-Hermitian system feature eigenvalue coalescence and non-trivial eigenvector degeneracies. Utilization of the rank-nullity theorem and graphical analysis of the phase rigidity factor enable identification of true exceptional points. Furthermore, this investigation achieves vectorized Zak phase quantization and examines a topolectric RLC circuit to derive the corresponding topological boundary resonance condition and the quantum Hall susceptance. Although Chern number quantization is not feasible, staggered hopping amplitudes corresponding to unit-cell lattice sites lead to broken inversion symmetry with non-zero Berry curvature, resulting in finite anomalous Nernst conductivity.
Figures
Figures from the paper (2 more)
Reference graph
Works this paper leans on
-
[52]
H. Shen, B. Zhen, and L. Fu, Phys. Rev. Lett. 120, 146402 (2018)
2018
-
[1]
S. H. Liu, W.L. Gao, Q. Zhang, et al., [J]. Research, 2019: 8609875 (2019)
work page 2019
-
[2]
Zak Phase and Topolectric RLC Circuit (A)Zak Phase For non-Hermitian systems, the Zak phase undergoes modification due to the loss of time- reversal symmetry and the possibility of complex eigenvalues. In particular, the Zak phase for a 2D non-Hermitian SSH model represents a generalization of the 1D case (the Zak phase in 1 D is essentially an integral, ...
-
[3]
In non-Hermitian systems (𝛾 ≠ 0) , exceptional points and broken symmetries can complicate causing edge modes to lose robustness or abrogate BBC. To resolve this, bi-orthonormal inner products have been employed in the analysis here without disrupting PT symmetry. This facilitates precise predictions of edge states as shown in Figure 4(c) and 4(d). In thi...
-
[4]
Staggered Hopping Amplitudes he presence of non-zero Berry curvature in systems with broken TRS/IS gives rise to an anomalous velocity, generally, resulting in an anomalous transport current and intrinsic Hall conductivity. In this section, apart from disrupted TRS (𝛾≠ 0), we investigate a scenario where the hopping amplitudes are staggered ( 𝑢 ≠ 𝑡ଵ, and/...
-
[5]
Our model Hamiltonian's energy eigenvalues are given by the quartic 𝑄,,ఊ(𝜆)= 0
Concluding remarks and future perspective This paper explores a 2D non-Hermitian variant of the SSH model. Our model Hamiltonian's energy eigenvalues are given by the quartic 𝑄,,ఊ(𝜆)= 0. We find that decreasing the numerical value of the tunable gain/loss parameter 𝛾 transforms the system from an insulator to a conductor. Notably, when 𝐽 = 0, 𝑄,ఊ(𝜆)= 0...
- [6]
-
[7]
W.P. Su, J.R. Schrieffer, A. J. and Heeger, Phys. Rev. Lett. 42, 1698 (1979)
work page 1979
Show all 56 references
-
[8]
Orlov, G.V
P. Orlov, G.V. Shlyapnikov, and D.V. Kurlov, Phys. Rev. B 111, L081105 (2025). 5.R. Nehra and D. Roy, Phys. Rev. B 105, 195407 (2022)
2025
-
[9]
V. M. Alvarez, J. B. Vargas, and L. F. Torres, Phys. Rev. B 97, 121401 (2018)
2018
-
[10]
Kawabata, T
K. Kawabata, T. Bessho, and M. Sato, Phys. Rev. Lett. 123, 066405 (2019)
2019
-
[11]
C. C. Ye, W.L. Vleeshouwers, et al., Phys. Rev. Research 6, 023202 (2024)
2024
-
[12]
Ashida, Z
Y. Ashida, Z. Gong, and M. Ueda, Adv. Phys. 69 249 (2020)
2020
-
[13]
Kawabata, K
K. Kawabata, K. Shiozaki, et al., Phys. Rev. X 9 041015 (2019)
2019
-
[14]
J. D. Lin, P. C. Kuo, et al., arXiv:2406.18362 (2024)
2024 arXiv
-
[15]
Wojcik, K
C.C. Wojcik, K. Wang, et al., Phys. Rev. B 106, L161401 (2022)
2022
-
[16]
Alase, S
A. Alase, S. Karuvade, and C. M. Scandolo, J. Phys. A: Math. Theor. 55 244003(2022)
2022
-
[17]
Ryu, J.H
J.W. Ryu, J.H. Han, et al., Commun Phys 7, 109 (2024)
2024
-
[18]
C. M. Bender, Rep. Prog. Phys. 70 947 (2007)
2007
-
[19]
Mandal and E
I. Mandal and E. J. Bergholtz, Phys. Rev. Lett. 127 186601(2021)
2021
-
[20]
J. Zak. Phys. Rev. Lett., 62 27472750 (1989)
1989
-
[21]
Delplace, D
P. Delplace, D. Ullmo, and G. Montambaux. Phys. Rev. B, 84 195452(2011). 19.J. Dong, V. Juricic, et al., Phys. Rev. Research 3 , 023056 (2021)
2011
-
[22]
Hoffmann, T
T. Hoffmann, T. Helbig, et al., Phys. Rev. Research2, 023265(2020). 21.D. Geng, H. Zhou, et al., Nat Commun 13, 7000 (2022)
2020
-
[24]
Okuma, K
N. Okuma, K. Kawabata, K. Shiozaki, and M. Sato, Phys. Rev. Lett. 124, 086801 (2020)
2020
-
[25]
Kawabata, N
K. Kawabata, N. Okuma, and M. Sato, Phys. Rev. B 101, 195147 (2020)
2020
-
[26]
Zhang, T
X. Zhang, T. Zhang, et al., Adv. Phys.: X 7, 2109431 (2022)
2022
-
[27]
H. Gao, H. Xue , et al., arXiv:2007.01041 v1[cond-mat. mes- hall](2020)
2020 arXiv
-
[28]
Yao and Z
S. Yao and Z. Wang, Phys. Rev. Lett. 121, 086803 (2018)
2018
-
[29]
S. Yao, F. Song, and Z. Wang, Phys. Rev. Lett. 121, 136802 (2018)
2018
-
[30]
F. K. Kunst, E. Edvardsson, et al., Phys. Rev. Lett. 121, 026808 (2018)
2018
-
[31]
Yokomizo and S
K. Yokomizo and S. Murakami, Phys. Rev. Lett. 123, 066404 (2019)
2019
-
[32]
Yi and Z
Y. Yi and Z. Yang, Phys. Rev. Lett. 125, 186802 (2020)
2020
-
[33]
Z. Yang, K. Zhang, et al., Phys. Rev. Lett. 125, 226402 (2020)
2020
-
[35]
Ghatak, M
A. Ghatak, M. Brandenbourger, et al., Proc. Natl. Acad. Sci. U.S.A. 117, 29561 (2020). 36.L. Xiao, T. Deng, et al., arXiv:2009.07288v2 [quant-ph] (2021)
2020 arXiv
-
[37]
K.G.Wilson, Phys. Rev. D 10, 2445 (1974)
1974
-
[38]
H. Wang, X. Tang, H. Xu, et al. npj Quantum Mater. 7, 61 (2022)
2022
-
[39]
Kim, and J
M. Kim, and J. Rho, Nanophotonics, vol. 9, no. 10, 3227(2020)
2020
-
[40]
C.H.Lee, S.Imhof, et al., Commun Phys 1, 39 (2018). 41.R. Yang Qi Xun, Molecular Frontiers Journal, 04(Supp01) 9 (2020)
2018
-
[42]
Blais, A
A. Blais, A. L. Grimsmo, S. M. Girvin, and A. Wallraff, Rev. Mod. Phys., 93 025005, (2021). 43.J. Dong, V. Juričić, et al., Phys. Rev. Res., 3 023056 (2021)
2021
-
[44]
J. C. Perez-Pedraza, and J. E. Barrios-Vargas, arXiv:2402.05261v1 [cond-mat.mtrl-sci] (2024)
2024 arXiv
-
[45]
Fang, G.-Y
A. Fang, G.-Y. Huang, et al., J. Phys. Commun.4 115006(2020)
2020
-
[46]
Leykam, K
D. Leykam, K. Y. Bliokh, C. Huang, Y. D. Chong, and F. Nori, Phys. Rev. Lett. 118, 040401 (2017)
2017
-
[47]
T. Gao, E. Estrecho, K. Y. Bliokh, T. C. H. Liew, M. D. Fraser, S. Brodbeck, M. Kamp, C. Schneider, S. Höfling, Y. Yamamoto,F.Nori, Y.S.Kivshar, A.G.Truscott, R.G.Dall, andE.A.Ostrovskaya, Nature 526, 554–558 (2015)
2015
-
[48]
Septembre, P
M.Król, I. Septembre, P. Oliwa, M. Kędziora, K. Łempicka-Mirek, M. Muszyński, R. Mazur, P. Morawiak, W. Piecek, P. Kula, W. Bardyszewski, P. G. Lagoudakis, D. D. Solnyshkov, G. Malpuech, B. Piętka, and J. Szczytko, Nat. Commun. 13, 5340 (2022)
2022
-
[49]
H. Zhou, C. Peng, Y. Yoon, C. W. Hsu, K. A. Nelson, L. Fu, J. D. Joannopoulos, M. Soljačić, and B. Zhen, Science 359, 1009–1012 (2018)
2018
-
[50]
R. Su, E. Estrecho, D. Biegańska, Y. Huang, M. Wurdack, M. Pieczarka, A. G. Truscott, T. C. H. Liew, E. A. Ostrovskaya, and Q. Xiong, Sci. Adv. 7, eabj8905 (2021)
2021
-
[51]
Zhang, Z
K. Zhang, Z. Yang, and C. Fang, Phys. Rev. Lett. 125, 126402 (2020)
2020
-
[53]
F. D. M. Haldane, Phys. Rev. Lett. 93, 206602(2004)
2004
-
[54]
Chen and S
M. Chen and S. Wan, J. Phys. Condens. Matter 24, 325502 (2012)
2012
-
[55]
D. Xiao, Y. Yao, Z. Fang, and Q. Niu, Phys.Rev. Lett. 97, 026603 (2006)
2006
-
[56]
Xiao, M.-C
D. Xiao, M.-C. Chang, Q. Niu, Rev. Mod. Phys. 82, 1959-2007 (2010)
2010
-
[57]
Fukui, Y
T. Fukui, Y. Hatsugai, and H. Suzuki, J. Phys. Soc. Jpn. 74, 1674 (2005)
2005
-
[58]
Str-el] (2024)
Masaaki Nakamura and Shohei Masuda, arXiv:2401.12674v1[ cond-mat. Str-el] (2024)
2024 arXiv
-
[59]
Asboth, L
J.K. Asboth, L. Oroszl´any, et al.,, A short course on topological insulators, Lect. Notes Phys. 919, 1 (2016). 60.T.L. Hughes, E. Prodan, and B. A. Bernevig, Phys. Rev. B 83, 245132 (2011). 61.G. van Miert, C. Ortix and C. Morais Smith, 2D Mater. 4, 015023(2017)
2016
-
[62]
R. Lin, T. Tai, L. Li and C.H. Lee , Frontiers of Physics, 18(5), 53605 (2023)
2023
-
[63]
Hou, G.Wu, et al., Phys
C. Hou, G.Wu, et al., Phys. Rev. B 109, 205135 (2024). Appendix A The right eigenstates linked to the eigenvalues of (5) could be written down in an explicit manner as |𝑢()൫𝑘௫,𝑘௬ ൯ൿ= 𝑁𝑗0 −1 2ф𝑗൫𝑘𝑥,𝑘𝑦൯, where ф൫𝑘௫,𝑘௬൯ is the transpose of the row vector ( 𝜓ଵ ()(𝒌) 𝜓ଶ ()(𝒌) 𝜓...
2024
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