REVIEW 4 major objections 4 minor 37 references
Variation of Bose surface by Filling in Cooper pair Bose metal
T0 review · 4 major / 4 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read A moderate next-nearest-neighbor hopping term enlarges the Cooper-pair Bose metal phase to half filling, where it coexists with charge order instead of being destroyed by it.
desk verdict A careful extension of the authors' own CPBM program: the filling axis at t'/t=0.2 yields plausible new coexistence and BS co-rotation, but missing error bars and constrained-path bias checks leave the boldest claims unproven. 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 central object is the effective momentum-resolved pairing distribution $N^{\mathrm{eff}}_{s\text{-pair}}(k)$, whose connected on-site pair correlations develop a finite-momentum ridge—the Bose surface—in the CPBM. The charge structure factor $N_c(k)$ separates incommensurate density waves from the commensurate $(\pi,\pi)$ CDW, and the two-boson correlator $P^{\mathrm{eff}}_{\zeta}(k)$ resolves the internal pairing channel. The geometric argument is carried by two rotation angles $\theta_F$ and $\theta_B$, both defined from the line joining upper and lower midpoints of the Fermi-surface intersections or Bose-surface maxima with the $k_y = 0$ axis; comparing them across fillings and $t'$ values is what produces the locking-then-co-rotation picture.
What would settle it
Recompute the same observables with a sign-problem-free or bias-controlled algorithm at ($t'/t$, $n$, $\alpha$) = (0.2, 0.982, 0.2) and (0.8, 0.523, 0.1); if the finite-momentum peak in $N^{\mathrm{eff}}_{s\text{-pair}}(k)$ vanishes at $n > 0.95$, or if $\theta_B$ does not systematically grow with $\theta_F$ across $t'/t = 0.2$, 0.5, 0.8, then the coexistence and co-rotation are artifacts of the approximation.
Extended reading notes
Core claim
On the model's own terms, the discovery is that at $t'/t = 0.2$ the CPBM phase, diagnosed by a finite-momentum peak in the connected on-site pairing distribution $N^{\mathrm{eff}}_{s\text{-pair}}(k)$, survives up to $n = 1.0$ for spin anisotropy $\alpha \lesssim 0.38$ and coexists with a commensurate $(\pi, \pi)$ charge-density wave for $n > 0.95$, whereas at $t' = 0$ the same high-filling region is CDW-dominated. The Bose surface is not rigid: when the non-interacting Fermi surface is rotated only mildly by $t'$, the Bose surface stays pinned to the lattice directions ($\theta_F \approx 8.7^\circ$, $\theta_B \approx 0^\circ$ at $t'/t = 0.2$), but stronger frustration makes the two surfaces co-rotate, with $\theta_B \approx 31^\circ$ when $\theta_F \approx 26^\circ$ at $t'/t = 0.8$. Internally, the dominant bosonic pairing channel is $d_{xy}$-wave at $t'/t = 0.2$ across all fillings, while at $t'/t = 0.8$ it shifts with filling from the third-nearest-neighbor $d^{(2)}_{x^2-y^2}$-wave at low $n$ to the nearest-neighbor $d^{(1)}_{x^2-y^2}$-wave at high $n$. These results are presented as evidence that filling and next-nearest-neighbor hopping act as complementary control levers for the CPBM.
Load-bearing premise
The load-bearing premise is that the constrained-path quantum Monte Carlo constraint used to tame the sign problem does not bias pairing correlations differently at high filling and strong anisotropy—the exact region where the enlarged CPBM, the CPBM–CDW coexistence, and the Bose-surface co-rotation are claimed.
Editorial extensions
If this is right
- At $t'/t = 0.2$ the CPBM region runs to $n \approx 1.0$ for $\alpha \lesssim 0.38$, so the phase should be reachable at weaker spin anisotropy and near half filling than the $t' = 0$ model allows.
- For $n > 0.95$ the Bose metal and a commensurate $(\pi, \pi)$ charge-density wave coexist at $t'/t = 0.2$, whereas $t' = 0$ leaves the high-filling regime to charge order alone.
- The Bose surface stays lattice-aligned for weak Fermi-surface rotation and then co-rotates, making the pairing-distribution peak orientation a direct readout of Fermi-surface geometry.
- At larger $t'$ the leading pairing channel changes with filling, from third-nearest-neighbor $d^{(2)}_{x^2-y^2}$ at low $n$ to nearest-neighbor $d^{(1)}_{x^2-y^2}$ at high $n$.
- CPBM stability is tied more to Fermi-surface anisotropy than to whether the Fermi surface is open or closed, so the phase should survive topological changes of the Fermi surface.
Reading between the lines
- The paper's locking-then-co-rotation picture suggests that measuring the Bose-surface orientation in a momentum-resolved cold-atom experiment could serve as a proxy for the Fermi-surface rotation angle, even where single-particle spectral functions are hard to resolve.
- The filling-controlled pairing crossover at large $t'$ implies a concrete experimental dial: in spin-dependent optical lattices, sweeping the filling should switch the dominant pairing channel, which could be detected through momentum-resolved pair correlations.
- Because the same geometric frustration that suppresses the CDW at $(\pi,\pi)$ also rotates the nesting vectors, the mechanism may extend to other commensurate instabilities in frustrated Hubbard models; this is an extension rather than a claim of the paper.
- The four reported angle pairs leave open whether the co-rotation is a sharp threshold or a smooth crossover; mapping $\theta_B$ against $\theta_F$ at more $t'$ values would settle that.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This manuscript uses constrained-path quantum Monte Carlo (CPQMC) to study the two-dimensional spin-anisotropic attractive Hubbard model with next-nearest-neighbor (NNN) hopping t'. It reports a zero-temperature phase diagram in the filling–anisotropy plane at t'/t = 0.2, finding that moderate NNN hopping enlarges the Cooper pair Bose metal (CPBM) phase, makes it persist up to half-filling, and leads to coexistence with commensurate CDW order for n > 0.95. It also reports a geometric coupling between the Fermi surface (FS) and the Bose surface (BS): the BS remains lattice-aligned for weak FS rotation but co-rotates when FS rotation becomes large. Finally, it analyzes symmetry-resolved pairing channels, finding d_xy-wave dominance at t'/t = 0.2 and a filling-dependent crossover among d-wave channels at t'/t = 0.8. The central claims are the enlarged CPBM region, the CPBM–CDW coexistence at high filling, and the BS co-rotation threshold.
Significance. If the CPQMC results are reliable, this work provides a concrete two-dimensional model in which carrier filling and NNN hopping act as complementary control parameters for a non-superfluid paired metallic phase, with observable signatures (Bose surface orientation, pairing symmetry, coexistence with CDW) that can guide cold-atom and correlated-electron searches. The paper is systematic: it uses a well-defined observable (Eq. 2), scans a broad parameter range, and accompanies the main phase diagram with momentum- and real-space diagnostics. It also contains falsifiable predictions, such as the BS-locking-to-co-rotation crossover and the filling-dependent change of dominant pairing symmetry at larger t'. However, the numerical evidence for the central claims is not yet fully robust: statistical errors are absent, finite-size scaling is performed only at t' = 0.8, and no trial-wavefunction sensitivity test is provided for the CPQMC constraint, leaving the most novel claims exposed to systematic bias.
major comments (4)
- [Sec. III A, Fig. 1(a); Sec. III B, Fig. 6] No statistical error bars are shown for any observable, yet the phase boundaries in Fig. 1(a) and the rotation angles θ_B in Fig. 6 are extracted from the positions of maxima of N^eff_s-pair(k) on a 16×16 lattice. Given the noisiness typical of CPQMC and the sensitivity of peak-position diagnostics to statistical fluctuations, the authors should provide error bars (or at least several independent runs) for the phase-boundary points and for θ_B, θ_F. Without this, the quantitative boundary at n = 1.0 and the threshold-like co-rotation claim are not supported at the stated precision.
- [Sec. II, Eq. (2); Sec. III B] The central observable N^eff_s-pair(k) is a connected pairing momentum distribution computed within the constrained-path approximation. The trial wavefunction for this spin-anisotropic model necessarily contains a spin-split Fermi surface with pair momentum Q = k_F↑ + k_F↓, and the constraint prevents walkers from crossing the trial nodal surface. The finite-momentum ridge in N^eff_s-pair(k) and the derived θ_B may therefore inherit the trial wavefunction's Fermi-surface geometry even in the absence of a true CPBM ground state. The manuscript provides no released-node calculation, no comparison against exact diagonalization in the CPBM regime, and no variation of the trial wavefunction to demonstrate that the ridge positions and the co-rotation behavior are intrinsic. This is a load-bearing gap because the enlarged CPBM region and the BS co-rotation claim rest entirely on this observable.
- [Appendix A, Fig. 9] The finite-size scaling analysis is performed only at t'/t = 0.8, and it addresses the scaling of N^eff_s-pair(k_max) and N_c(k_max) at selected points, not the quantities that define the main phase diagram at t'/t = 0.2. In particular, there is no finite-size scaling at representative points along the CPBM–s-SF boundary of Fig. 1(a), nor any scaling test of the BS rotation angles θ_B shown in Fig. 6. The claim that the t' = 0.2 phase boundaries persist in the thermodynamic limit is therefore not directly supported by the presented data.
- [Sec. III A, Figs. 1(d)–(f) and 3(e)] The CPBM–CDW coexistence for n > 0.95 rests on essentially a single parameter set, (n, α) = (0.982, 0.20), and the evidence is that N_c(k) has a sharp (π, π) peak while N^eff_s-pair(k) still shows a finite-momentum ridge. The authors do not perform a joint finite-size scaling of the pairing and charge signals at this point, nor do they trace the coexistence region in the (n, α) plane. The statement 'coexists with a commensurate CDW' is stronger than 'both signals are present on a 16×16 lattice'; it requires demonstrating that both the CPBM ridge and the CDW peak survive in the thermodynamic limit.
minor comments (4)
- [Sec. II, Eq. (3)] In Eq. (3), the exponential should read exp[i k · (r_i − r_j)]; the dot product is missing. Also, the definition of C_CDW is given as ⟨n_i n_j⟩, but later C_CDW(r_x) is used without indicating whether this is the connected part; please clarify.
- [Sec. II, Eq. (5)] The Green's function notation G^σ_{i,j} = ⟨c_{iσ} c†_{jσ}⟩ is unusual; the conventional definition is G^σ_{i,j} = ⟨c_{iσ} c†_{jσ}⟩ (or its Hermitian conjugate), but the subsequent subtraction in Eq. (5) relies on a specific ordering. Please state the convention explicitly so the connected correlator is unambiguous.
- [Sec. III B, Fig. 5(a)] In Fig. 5(a), the t' = 1.0 curve (red pentagons) is included in the legend but the main text (Sec. III B) only discusses t' = 0, 0.2, 0.5, and 0.8. Either remove the t' = 1.0 data or comment on it consistently.
- [Sec. III A, Fig. 1(a)] The gray dashed line for the t' = 0 boundary is said to reproduce Ref. [22], but the reader cannot verify this without error bars or a comparison of the underlying data. It would be helpful to state explicitly whether this boundary is taken from the previous paper or recalculated here.
Circularity Check
No significant circularity: self-citations are contextual, and the new CPBM phase boundaries and Bose-surface rotation results are read directly from CPQMC observables rather than from fitted targets or prior conclusions.
full rationale
The paper's central claims are not equivalent to their inputs. No parameter is fitted to a target observable: U=-3 is fixed, and t', n, alpha are scanned; phase boundaries are read from the momentum structure of N_eff_s-pair(k) (Eq. 2) and N_c(k) (Eq. 3). The finite-momentum peak in the connected pairing distribution is the defining diagnostic of a Bose surface, and the real-space decay is a separate check, so classifying s-SF versus CPBM is a measurement rather than a tautology. The theta_B rotation angle is obtained from the four maxima of N_eff_s-pair(k), not from the non-interacting Fermi-surface contours used for theta_F, so the co-rotation is an observed correlation rather than an identity by construction. The self-citations [22,23] provide the t'=0 comparison boundary and the P_eff_zeta correlator definition, but the t'=0 CPBM collapse at (0.982,0.20) is reproduced in the paper's own Fig. 1(f), and the t'=0.2 enlargement and coexistence claims are supported by the present CPQMC data. The finite-size scaling in Appendix A at t'=0.8 is a validation gap, and the constrained-path bias is a correctness risk, but neither reduces to a circular argument.
Assumptions & free parameters
free parameters (1)
- Interaction strength U =
-3 (in units of t)
assumptions (4)
- domain assumption CPQMC constrained-path approximation gives unbiased ground-state expectation values for this model.
- domain assumption A finite-momentum peak in N^eff_s-pair(k) together with short-range real-space decay identifies a CPBM rather than a finite-size or superfluid artifact.
- domain assumption Non-interacting Fermi-surface topology and rotation are adequate proxies for the interacting FS geometry.
- domain assumption Finite-size scaling on L=8,12,16 at representative points, mostly at t'=0.8, is sufficient to conclude that all four phases persist in the thermodynamic limit.
Cite this review
Pith. "Pith review of Variation of Bose surface by Filling in Cooper pair Bose metal." pith.science (2026). https://pith.science/paper/2UBZZCHG
@misc{pith2026250524405,
author = {Pith},
title = {Pith review of: Variation of Bose surface by Filling in Cooper pair Bose metal},
year = {2026},
howpublished = {\url{https://pith.science/paper/2UBZZCHG}},
note = {Machine review of arXiv:2505.24405}
}
read the original abstract
The Cooper pair Bose metal (CPBM) is a non-superfluid quantum phase in which uncondensed fermion pairs form a "Bose surface" in momentum space. We investigate the CPBM in the two-dimensional spin-anisotropic attractive Hubbard model by tuning the next-nearest-neighbor (NNN) hopping t', carrier filling n, and spin anisotropy alpha, using large-scale constrained-path quantum Monte Carlo simulations. A moderate NNN hopping (t'/t = 0.2) substantially enlarges the CPBM region: the phase extends into weaker anisotropy regimes and coexists with a commensurate charge-density wave (CDW) near half-filling (n > 0.95), where CDW order would otherwise dominate at t' = 0. Interestingly, t' suppresses the overall CDW peak amplitude and introduces a geometric correlation between the orientations of the Fermi and Bose surfaces: for weak Fermi-surface rotations, the Bose surface remains aligned with the lattice axes, while larger distortions drive both surfaces to rotate in tandem. Momentum-resolved pairing distributions reveal that the bosonic pairing channels are jointly controlled by t' and carrier filling n. For small t', d_xy-wave correlations dominate across the entire filling range. In contrast, for larger t', the dominant pairing symmetry varies with n, reflecting a nontrivial interplay between frustration and density. These findings establish carrier filling and NNN hopping as complementary levers for manipulating CPBM stability and provide concrete criteria for identifying non-superfluid bosonic matter in cold-atom and correlated-electron systems.
Figures
Figures from the paper (6 more)
Reference graph
Works this paper leans on
-
[1]
L. D. Landau, The theory of a fermi liquid, Sov. Phys. JETP3, 920 (1957)
work page 1957
-
[2]
P. W. Anderson,The Theory of Superconductivity in the High-Tc Cuprates(Princeton University Press, 1998)
work page 1998
-
[3]
D. Pines and P. Nozi` eres,The Theory of Quantum Liq- uids(Addison-Wesley, 1966)
work page 1966
-
[4]
P. Abbamonte, P. Phillips, and N. E. Hussey, The strange metal problem, Science377, eabh4273 (2022)
work page 2022
-
[5]
Q. Si, S. Rabello, K. Ingersent, and J. L. Smith, Hidden order and quantum criticality in heavy fermions, Nature 492, 419 (2012)
work page 2012
-
[6]
P. W. Anderson, The resonating valence bond state in la2cuo4 and superconductivity, Science235, 1196 (1987)
1987
-
[7]
Y. Li, H. Liu, H. Ji, C. Ji, S. Qi, X. Jiao, W. Dong, Y. Sun, W. Zhang, Z. Cui, M. Pan, N. Samarth, L. Wang, X. C. Xie, Q. K. Xue, Y. Liu, and J. Wang, High- temperature anomalous metal states in iron-based in- terface superconductors, Phys. Rev. Lett.132, 226003 (2024)
work page 2024
-
[8]
H. Sun, M. Huo, X. Hu, J. Li, Z. Liu, Y. Han, L. Tang, Z. Mao, P. Yang, B. Wang, J. Cheng, D.-X. Yao, G.-M. Zhang, and M. Wang, Signatures of superconductivity near 80 k in a nickelate under high pressure, Nature621, 493 (2023)
2023
Show all 37 references
-
[9]
G. Wang, N. N. Wang, X. L. Shen, J. Hou, L. Ma, L. F. Shi, Z. A. Ren, Y. D. Gu, H. M. Ma, P. T. Yang, et al., Pressure-induced superconductivity in polycrys- talline la3ni2o7, Phys. Rev. X14, 011040 (2024)
2024
-
[10]
P. W. Phillips, N. E. Hussey, and P. Abbamonte, Stranger than metals, Science377, eabh4273 (2022), https://www.science.org/doi/pdf/10.1126/science.abh4273
2022 doi
-
[11]
Keimer, S
B. Keimer, S. A. Kivelson, M. R. Norman, S. Uchida, and J. Zaanen, From quantum matter to high-temperature superconductivity in copper oxides, Nature518, 179 (2015)
2015
-
[12]
Hashimoto, I
M. Hashimoto, I. M. Vishik, R.-H. He, T. P. Dev- ereaux, and Z.-X. Shen, Energy gaps in high-transition- temperature cuprate superconductors, Nature Physics 10, 483 (2014)
2014
-
[13]
Q. Chen, Z. Wang, R. Boyack, S. Yang, and K. Levin, When superconductivity crosses over: From bcs to bec, Rev. Mod. Phys.96, 025002 (2024)
2024
-
[14]
M. S. Block, R. V. Mishmash, R. K. Kaul, D. N. Sheng, O. I. Motrunich, and M. P. A. Fisher, Exotic gapless mott insulators of bosons on multileg ladders, Phys. Rev. Lett. 106, 046402 (2011)
2011
-
[15]
Das and S
D. Das and S. Doniach, Bose metal: Gauge-field fluctu- ations and scaling for field-tuned quantum phase transi- tions, Phys. Rev. B64, 134511 (2001)
2001
-
[16]
The CPBM signal remains nearly flat, indicating short- range pairing, while the s-SF signal increases with system size, consistent with long-range coherence.(b) Same analy- sis atn= 0.900, showing consistent behavior:N eff s-pair(kmax) remains size-independent for CPBM, but gr...
-
[17]
Shinet al., Controlled suppression of the field- induced bose metallic state via disorder tuning in a two- dimensional superconducting system, Phys
J. Shinet al., Controlled suppression of the field- induced bose metallic state via disorder tuning in a two- dimensional superconducting system, Phys. Rev. B111, 054506 (2025)
2025
-
[18]
Phillips and D
P. Phillips and D. Dalidovich, The elusive bose metal, Science302, 243 (2003)
2003
-
[19]
Zhang, A
Y. Zhang, A. M. DaSilva, J. Lee, J. J. Koralek, J. P. Hinton, J. D. Koralek, J. Lee, J. P. Hinton, J. J. Koralek, J. Lee,et al., Bosonic metallic state in the superconductor-insulator transition, Science366, 1505 (2019)
2019
-
[20]
D. N. Sheng, O. I. Motrunich, S. Trebst, E. Gull, and M. P. A. Fisher, Strong-coupling phases of frustrated bosons on a two-leg ladder with ring exchange, Phys. Rev. B78, 054520 (2008)
2008
-
[21]
A. E. Feiguin and M. P. A. Fisher, p-wave superfluidity by spin-nematic fermi surface deformation, Phys. Rev. Lett.103, 025303 (2009)
2009
-
[22]
A. E. Feiguin and M. P. A. Fisher, Exotic paired phases in ladders with spin-dependent hopping, Phys. Rev. B 83, 115104 (2011)
2011
-
[23]
Z. Cao, J. Su, J. Li, T. Ying, W. Wang, J.-H. Sun, H.-K. Tang, and H.-Q. Lin, Exotic d-wave cooper pair bose metal in two dimensions, Phys. Rev. B110, 224522 (2024)
2024
-
[24]
Z. Cao, J. Li, J. Su, T. Ying, and H.-K. Tang, d x2−y2 - wave bose metal induced by next-nearest-neighbor hop- ping anisotropy, Phys. Rev. B111, 134512 (2025)
2025
-
[25]
Z. B. Huang, H. Q. Lin, and J. E. Gubernatis, Quan- tum monte carlo study of spin, charge, and pairing cor- relations in the t–t’–u hubbard model, Phys. Rev. B64, 205101 (2001)
2001
-
[27]
Zhang, J
S. Zhang, J. Carlson, and J. E. Gubernatis, Constrained path quantum monte carlo method for fermion ground states, Phys. Rev. Lett.74, 3652 (1995)
1995
-
[28]
Zhang, J
S. Zhang, J. Carlson, and J. E. Gubernatis, Constrained path monte carlo method for fermion ground states, Phys. Rev. B55, 7464 (1997)
1997
-
[29]
Comin and A
R. Comin and A. Damascelli, Resonant x-ray scattering studies of charge order in cuprates, Annu. Rev. Condens. Matter Phys.7, 369 (2016)
2016
-
[30]
X. Teng, L. Chen, F. Ye, Z. Wang, J.-X. Yin, Y. Hu, Z. Yang, Y.-X. Jiang, J. Shan, T.-R. Chang, W. Shi, D. Gong, S. X.-M. Riberolles, M. D. Frontzek, S. Desgre- niers, H. B. Cao, H. Lin, M. Z. Hasan, G. Xu, Z. Wang, G. Chen, Q. Liu, D. Feng, and C. Jin, Discovery of charge den...
2022
-
[31]
O. I. Motrunich and M. P. A. Fisher,d-wave correlated critical bose liquids in two dimensions, Phys. Rev. B75, 235116 (2007)
2007
-
[32]
Jiang, M
H.-C. Jiang, M. S. Block, R. V. Mishmash, J. R. Garri- son, D. Sheng, O. I. Motrunich, and M. P. Fisher, Non- fermi-liquid d-wave metal phase of strongly interacting electrons, Nature493, 39 (2013)
2013
-
[33]
Serwane, G
F. Serwane, G. Z¨ urn, T. Lompe, T. B. Ottenstein, A. N. Wenz, and S. Jochim, Deterministic preparation of a tun- able few-fermion system, Science332, 336 (2011)
2011
-
[34]
Y.-Y. Jau, A. M. Hankin, T. Keating, I. H. Deutsch, and G. W. Biedermann, Entangling atomic spins with a rydberg-dressed spin-flip blockade, Nature Physics12, 71 (2016)
2016
-
[35]
Zeiher, R
J. Zeiher, R. van Bijnen, P. Schauß, S. Hild, J.-Y. Choi, T. Pohl, I. Bloch, and C. Gross, Many-body interferome- try of a rydberg-dressed spin lattice, Nature Physics12, 1095 (2016)
2016
-
[36]
ˇSmejkal, J
L. ˇSmejkal, J. Sinova, and T. Jungwirth, Emerging re- search landscape of altermagnetism, Physical Review X 12, 040501 (2022)
2022
-
[37]
ˇSmejkal, J
L. ˇSmejkal, J. Sinova, and T. Jungwirth, Beyond conven- 12 tional ferromagnetism and antiferromagnetism: A phase with nonrelativistic spin and crystal rotation symmetry, Physical Review X12, 031042 (2022)
2022
-
[38]
J. Li, J. Liu, X. Yang, and H.-K. Tang, Enhancement of d-wave pairing in strongly correlated altermagnet (2025), arXiv:2505.12342 [cond-mat.str-el]
2025 arXiv
Reviewed August 7, 2026 · model on record in the stance chip above.
Discussion (0). Sign in to comment.