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REVIEW 4 major objections 4 minor 38 references

Electronic nematic normal and superconducting state in electron-doped copper-oxide superconductors

T0 review · 4 major / 4 minor · reviewed 2026-08-07 · deepseek-v4-flash

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Pith's one-line read An electron-doped cuprate superconductor spontaneously breaks in-plane rotational symmetry in both its normal state and its field-suppressed zero-temperature ground state, showing electronic nematicity is intrinsic to high-temperature…

desk verdict First credible case for electronic nematicity in an electron-doped cuprate, built on a known method and controlled by a substrate comparison; the main gaps are missing error bars and a cited, not shown, quantitative inversion. read the letter →

arxiv 2506.14077 v1 pith:OC7UK3OC submitted 2025-06-17 cond-mat.supr-con

J.Y. Shen , G.F. Chen , Y.C. Zhang , G.Y. Xi , J.Y. He , X.B. Cheng , J. Wu This is my paper · ORCID
classification cond-mat.supr-con
keywords electronicnematicityelectron-dopedcupratesSr0.9La0.1CuO2angle-resolvedresistivityhigh-temperaturesuperconductivitysuperconductingfluctuationsinfinite-layer
topics High-Temperature Superconductivity
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

High-temperature cuprate superconductors can be doped with holes or electrons, and the two families differ in many ways: electron-doped cuprates lack the pseudogap, have different crystal structures, and host carriers with different orbital character. This paper aims to show that despite those differences, the electron-doped infinite-layer cuprate Sr$_{0.9}$La$_{0.1}$CuO$_2$ (SLCO) is electronically nematic—it spontaneously picks out one in-plane direction—already in its normal state from room temperature down to its superconducting transition, and even in the zero-temperature ground state obtained when a magnetic field suppresses superconductivity. The authors report that the nematic amplitude is essentially unchanged whether the film is grown on a tetragonal or an orthorhombic substrate, while the nematic director follows the substrate strain only on the orthorhombic one, which they take as evidence that the order is driven by electron-electron correlations rather than by the lattice. The same nematic order strengthens when superconducting fluctuations appear near $T_c$ and grows further as the doping is lowered toward underdoping, matching the behavior seen in hole-doped La$_{2-x}$Sr$_x$CuO$_4$. The broader claim is that electronic nematicity is a generic property of high-temperature superconductors regardless of carrier type, a conclusion that would constrain theories of high-temperature superconductivity.

What carries the argument

The central mechanism is the angle-resolved resistivity (ARR) method, in which a four-terminal cross-shaped pattern rotates the current direction continuously within the CuO$_2$ plane by controlling the current components $I_x = I_0\cos\phi$ and $I_y = I_0\sin\phi$ and measuring both the longitudinal and transverse voltages at each angle. The resistivity tensor components are then fit to $\rho(\phi) = \overline{\rho} + \Delta\rho\cos[2(\phi-\alpha)]$ and $\rho_T(\phi) = \Delta\rho\sin[2(\phi-\alpha)]$, where the relative amplitude $N = \Delta\rho/\overline{\rho}$ quantifies the nematic strength and the phase $\alpha$ locates the nematic director. The key work of this machinery is to map the full 360-degree angular dependence of both resistivities on one small, uniform region of the film, so that the measured oscillations can be separated from sample inhomogeneity and contact artifacts by their dependence on temperature, strain, and magnetic field.

What would settle it

Fabricate the same SLCO/KTO film into several independent ARR devices with different cross-arm widths, contact sizes, and current paths, and also measure a fixed-angle multi-Hall-bar device on the same area; if the extracted nematic amplitude $\Delta\rho$ and director $\alpha$ vary with geometry or disagree between methods, the angular oscillations reflect a measurement artifact rather than a bulk electronic nematicity.

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Extended reading notes

Core claim

The paper's central discovery is that electronic nematicity—the spontaneous breaking of in-plane fourfold (C4) rotational symmetry down to twofold (C2) symmetry—exists in an electron-doped cuprate superconductor, Sr$_{0.9}$La$_{0.1}$CuO$_2$, and that it pervades both the normal state and the state reached when superconductivity is extinguished by a magnetic field. Using angle-resolved resistivity measurements with a cross-shaped device that rotates the current direction continuously, the authors find that the longitudinal resistivity oscillates as $\overline{\rho} + \Delta\rho\cos[2(\phi-\alpha)]$ and the transverse resistivity as $\Delta\rho\sin[2(\phi-\alpha)]$, giving a nematic amplitude $N = \Delta\rho/\overline{\rho}$ of about 1.5% at 300 K and a director $\alpha$ that shifts with temperature and rotates abruptly near $T_c$. The nematic amplitude is not changed when the substrate is switched from tetragonal KTaO$_3$(001) (in-plane lattice orthorhombicity below 0.05%) to orthorhombic GdScO$_3$(110) (film orthorhombicity 0.38%), while the director is pinned by the orthorhombic strain; the authors take this near-independence of amplitude as proof that the nematicity is electronic in origin. When a magnetic field of up to 16 T suppresses superconductivity at low temperature, the normal-state nematic amplitude and director are recovered at all temperatures below $T_c$, so the zero-temperature ground state is nematic. The nematicity also grows as the effective doping is reduced from optimal to underdoped, closely paralleling the behavior previously reported in hole-doped LSCO.

Load-bearing premise

The paper assumes that the angle-resolved resistivity device measures the true bulk longitudinal and transverse resistivity of the film, meaning the current flow at the cross-shaped pattern is uniform enough that the measured voltages give the longitudinal and transverse components directly, without sizeable corrections from current spreading, contact misalignment, or geometric magnetoresistance.

Editorial extensions

If this is right

  • Electronic nematicity is a common feature of both hole- and electron-doped cuprate superconductors, so carrier type, crystal structure, and the presence or absence of a pseudogap are not prerequisites for nematic order.
  • The zero-temperature ground state of optimally doped SLCO, once superconductivity is removed by a magnetic field, is nematic rather than a conventional isotropic Fermi liquid.
  • Superconducting fluctuations in SLCO are themselves nematic, with a distinct director orientation and strongly enhanced amplitude near $T_c$, so superconductivity appears to develop out of a nematic-fluctuating state.
  • The near-independence of the nematic amplitude from a large applied orthorhombic lattice distortion, together with the pinning of the director, implies that the nematic order is electronically driven and only weakly coupled to the lattice.
  • The nematic amplitude grows as the effective doping is reduced from optimal to underdoped, matching the doping dependence seen in hole-doped LSCO and indicating the order is intrinsic to the cuprate family.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A testable extension of the paper's logic is that the same angle-resolved resistivity signatures should appear in other electron-doped cuprates such as Nd$_{2-x}$Ce$_x$CuO$_4$, and the director rotation near $T_c$ should scale with the strength of superconducting fluctuations; if not, the universality claim would need revision.
  • The near-independence of the nematic amplitude from substrate orthorhombicity implies a large electronic nematic susceptibility. Measuring the response of $N$ to uniaxial stress, or to a magnetic field applied along different in-plane directions, could map this susceptibility tensor and help distinguish spin- and charge-driven mechanisms.
  • If the zero-temperature ground state is truly nematic, the superconducting state that develops from it should show a two-fold anisotropy in its upper critical field, vortex lattice, or fluctuation conductivity even in nominally tetragonal films—an observable the present transport data do not directly address.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 4 minor

Summary. The manuscript reports angle-resolved resistivity (ARR) measurements on electron-doped infinite-layer Sr0.9La0.1CuO2 (SLCO) thin films grown on KTaO3(001) and GdScO3(110) substrates, claiming that the normal state is electronically nematic from room temperature down to the superconducting transition, that the superconducting-fluctuation state and the field-suppressed ground state are also nematic, and that the nematicity is electronic in origin because the nematic amplitude is nearly independent of the orthorhombic lattice distortion while the director is pinned by it. The paper also presents a doping series showing enhanced nematicity in underdoped films.

Significance. If correct, this would be the first observation of electronic nematicity in an electron-doped cuprate and would significantly strengthen the view that nematicity is a universal ingredient of high-temperature superconductivity. The paper uses a high-resolution ARR method with a useful gold-film control, a two-substrate comparison, and a field-suppression experiment to argue for an intrinsic electronic origin. The temperature-dependent rotation of the nematic director and the similarity of the doping dependence to hole-doped LSCO are potentially important. However, the manuscript's central quantitative claims currently rest on an unvalidated inversion for anisotropic samples and on fits without error bars, so the significance will be fully realized only after these issues are addressed.

major comments (4)
  1. [Page 4, description of ARR method and Eqs. (1)-(2)]
  2. [Fig. 2a and gold-film control paragraph]
  3. [Figs. 3e, 3f and Figs. 5g-5h]
  4. [Methods A1-A2 and Fig. 3]
minor comments (4)
  1. [Title and Abstract]
  2. [Eqs. (1)-(2)]
  3. [Page 8, extrinsic-factors paragraph]
  4. [Fig. 3c-3d]

Circularity Check

0 steps flagged · score 1.0 of 10

No constructional circularity: the ARR fits are measurements, not predictions, and the self-citations to prior ARR methodology are not load-bearing.

full rationale

The paper's central claim—that SLCO is electronically nematic in the normal state and in the field-suppressed zero-temperature state—is not circular. The claim is carried by measured 180°-periodic oscillations in ρ(φ) and ρ_T(φ) (Figs. 2c–2f), by the simultaneous fit of Δρ and α in Eqs. (1)–(2), by the temperature evolution of the peak angles, and by the controlled comparison between tetragonal KTO and orthorhombic GSO substrates. Δρ and α are fitting parameters extracted from the data, so calling Δρ/ρ the nematic amplitude is a definitional label for the observed anisotropy, not a prediction forced to match an assumed output. The only self-referential element is the citation of the authors' previous ARR papers (refs. 20 and 28) for the derivation of Eqs. (1)–(2) and for the methodology ('Detailed discussions on the ARR methodology can be found in our previous publication28'). These citations are not load-bearing: the equations are an elementary C2-symmetric transport parameterization, the raw angular scans are displayed and independently show the oscillations, a gold-film control demonstrates that the pattern itself does not create anisotropy, and the LSCO comparisons are external systems. No step in the derivation chain reduces by construction to its inputs; the ARR current-uniformity assumption is an instrumental validity concern, not a circularity.

Assumptions & free parameters 2 free parameters · 3 assumptions · 0 invented entities

The paper introduces no new theoretical entities or model parameters. The fitted DeltaRho and alpha are the primary measured quantities, not ad hoc tuning parameters. The main assumptions are the standard C2-symmetric transport parameterization, the fidelity of the ARR geometry, the equivalence of field-suppressed and zero-field normal states, and the negligibility of lattice distortion on KTO.

free parameters (2)
  • Nematic amplitude DeltaRho = varies from about 1.5% of Rho at 300 K to larger values near Tc (exact values not tabulated)
    Fitted coefficient of the cos2(phi-alpha) term in Eq. [1]; the entire nematicity claim depends on this being nonzero.
  • Nematic director alpha = e.g., 95.84 degrees at 300 K for SLCO/KTO; changes with temperature and substrate
    Fitted phase offset in Eqs. [1] and [2]; its temperature dependence is used to rule out extrinsic artifacts and to infer a rotation of the director near Tc.
assumptions (3)
  • domain assumption The resistivity tensor has a purely C2-symmetric angular form as given by Eqs. [1] and [2], with no higher angular harmonics.
    The data are fit to these two expressions; if additional harmonics or a non-uniform current distribution existed, the extracted DeltaRho and alpha would not cleanly isolate a nematic order parameter. The derivation is cited to refs 20 and 28.
  • domain assumption The magnetic-field-suppressed state below Tc is the same zero-temperature normal state as above Tc.
    The B-T phase diagram interpretation (Figs. 4e and 4f) assumes the magnetic field only suppresses superconductivity and does not intrinsically modify the electronic nematic order.
  • domain assumption SLCO on KTO has negligible orthorhombic lattice distortion (gamma <= 0.05%).
    The conclusion that the observed anisotropy is purely electronic depends on the XRD measurement showing gamma at or below instrumental resolution; the paper states gamma <= 0.05% (Table 1) but does not give an uncertainty.

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Cite this review

Pith. "Pith review of Electronic nematic normal and superconducting state in electron-doped copper-oxide superconductors." pith.science (2026). https://pith.science/paper/OC7UK3OC

@misc{pith2026250614077,
  author       = {Pith},
  title        = {Pith review of: Electronic nematic normal and superconducting state in electron-doped copper-oxide superconductors},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/OC7UK3OC}},
  note         = {Machine review of arXiv:2506.14077}
}
read the original abstract

The similarities and differences between hole- and electron-doped cuprates are central to studies of high-temperature superconductivity. While electronic nematicity is found to be pervasive in hole-doped cuprates, iron-based superconductors, and other unconventional superconductors, evidence for electronic nematicity in electron-doped cuprates remains elusive. Here, we discover that the normal state of electron-doped Sr0.9La0.1CuO2 (SLCO) is nematic by the angle-resolved resistivity (ARR) method and the uncovered ground state at zero temperature is also nematic when superconductivity is suppressed by an applied magnetic field. As we deliberately change the substrate from tetragonal KTaO3(001) (KTO) to orthorhombic GdScO3(110) (GSO), the nematic director of SLCO is pinned by the epitaxial strain but the nematic amplitude remains roughly the same, implying that the nematicity originates from electron-electron correlations. The nematicity is significantly enhanced by the presence of superconducting fluctuations and its amplitude increases appreciably as the effective doping level of SLCO is lowered from optimal to underdoped. Thus, electronic nematicity is intrinsic to high-temperature superconductors regardless of differences in the structural and electronic configurations corresponding to hole or electron doping.

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