{"id":"594b9694-b213-4a50-ada5-df3aa3f3a3e4","arxiv_id":"2506.21392","paper_version":1,"verdict":"CONDITIONAL","confidence":"LOW","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"A low-energy four-leaf clover-shaped electronic state, about two lattice units wide, exists in underdoped Bi-2212, fades with hole doping, and can be locally erased and restored by tip voltage.","lead":"Using a scanning tunneling microscope, the authors report a new four-leaf clover-shaped electronic pattern that appears at low energy in underdoped cuprate superconductors and disappears as doping increases. They also show that voltage pulses from the microscope tip can locally erase and restore the pattern, which they interpret as a tunable precursor to superconducting pairing.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The assignment of the 2a0 FLC conductance contrast to an intrinsic CuO2 low-energy electronic state is not yet established; the main-text controls are missing, and the manipulation result is confounded by visible Bi atom rearrangement.","rationale":"The paper reports a visually striking, apparently doping-dependent 2a0 electronic texture and a reversible field-induced change. In good faith, the observation could be real: the choice of p≈0.05 to maximize the effect is sensible, the 'kink' at 16 meV is a falsifiable energy scale, and the doping trend in Fig.2E-H is directionally consistent with the stated phase diagram. The reason the result cannot be accepted as stated is that every branch of the central claim—visualization, doping dependence, and manipulation—passes through the same unverified premise: the FLC contrast in g(r,16 meV) is an intrinsic low-energy electronic state of the CuO2 plane rather than a topographic, tip, or surface-layer artifact. The main text does not quantify the FLC density or compare conductance maps with topography; it relegates the only impurity/topographic controls to supplementary figures; and the electric-field experiment visibly moves surface Bi atoms, making the electronic interpretation degenerate with a structural one. These are standard, checkable STM confounds, not internal inconsistencies. The reader's weakest assumption identifies exactly this point, and I agree with it. A constant-height control and a topographic cross-talk normalization would settle the central concern; until then the appropriate disposition remains conditional rather than accept or reject.","tokens_in":7021,"tokens_out":6062,"duration_ms":73298,"concrete_test":"On the same p≈0.05 Bi-2212 crystal, acquire 16 mV dI/dV maps in constant-current mode at two set-point currents and then in constant-height mode with feedback disabled, recording the simultaneous z(x,y) corrugation. If the FLC lobes remain Cu-centered with unchanged relative amplitude after normalizing by the topographic transmission term, the topographic cross-talk explanation is excluded; if the pattern follows z corrugation, the intrinsic-state claim fails. For the manipulation claim, repeat the pulse sequence at a fixed surface marker using a freshly characterized tip apex and require FLC toggling with no Bi atom displacement in the simultaneously recorded topography.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim requires that the FLC pattern in g(r, 16 meV) is an intrinsic CuO2-plane electronic state, not a topographic or tip artifact. This attribution is load-bearing but weakly supported. Fig.1H presents representative FLC maps with no quantitative line traces, template counts, or direct comparison of g(r,16 meV) with simultaneously acquired topography, so standard STM cross-talk between z-feedback and low-bias dI/dV is not excluded. The stated impurity controls (g(r,-16 meV) and g(r,0 meV), Fig.S1/S2, ref.35) are not shown or analyzed in the main text. The manipulation section adds a further confound: Fig.3D-F show clear Bi atom movement after pulsing at 2.2-4.0 V, so the FLC disappearance and reappearance in Fig.3G-I is degenerate with a change in surface atomic configuration or tip apex state; no control separates local electric-field doping from surface reconstruction. If the FLC contrast is not intrinsic, the abstract's 'new electronic phase' and 'tunable electronic phase' claims lose their foundation. The reader's weakest assumption is therefore the right one, and it remains unresolved by the presented evidence.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript reports STM/STS measurements on Bi-2212 at four nominal hole dopings, p~0.05, 0.10, 0.15, and 0.19. The authors identify a 'four-leaf clover' (FLC) pattern in dI/dV maps at 16 mV, centered on Cu sites, with a characteristic low-energy spectral feature near 16 meV. They report that the apparent density of these FLC patterns decreases with doping and vanishes in the overdoped sample, and they demonstrate that voltage pulses from the STM tip can locally erase and restore the pattern. The paper interprets the FLC as the smallest real-space precursor unit for incoherent Cooper pairs and as a tunable electronic phase tied to the Mott-insulator potential landscape.","tokens_in":7281,"tokens_out":9168,"duration_ms":101095,"significance":"If the FLC pattern is an intrinsic low-energy electronic texture of the CuO2 planes, this would be a qualitatively new observation in underdoped cuprates, with direct relevance to precursor pairing and to the doping-dependent evolution of local electronic order. The manuscript has clear strengths: it surveys four dopings, uses atomically resolved STM, identifies a specific low-energy scale (16 meV), and includes an attempt at tip-induced manipulation with supplementary g(r,-16 meV) and g(r,0 meV) maps. The doping-dependence claim is falsifiable in principle. However, the main text does not yet establish that the FLC contrast is an intrinsic electronic state rather than a topographic or tip artifact, the doping dependence is not quantitatively demonstrated, and the manipulation result is confounded by concurrent Bi atom rearrangement. The work is therefore significant but conditional on substantially strengthened evidence and analysis.","major_comments":[{"comment":"The central claim that the FLC contrast in g(r, 16 meV) is an intrinsic CuO2-plane electronic state is not established by quantitative controls. Fig.1H is presented as a single representative map, but no line profiles, template counts, or comparison of g(r, 16 meV) with the simultaneously acquired topography are given, so standard topographic cross-talk in low-bias dI/dV is not excluded. The stated impurity-state exclusions, g(r, -16 meV) and g(r, 0 meV) in Figs.S1-S2 with ref. 35, are not shown or analyzed in the main text, and ref. 35 is a general review of impurity scattering rather than a control dataset. This missing control is load-bearing because the abstract's 'new electronic phase' claim rests on the FLC being an intrinsic state.","section":"Discovery of a 2a0 sized FLC electronic state at low-energy (Fig.1E-I)"},{"comment":"The doping dependence is presented only qualitatively. The text states that the number of FLC patterns decreases sharply and vanishes in the overdoped region, but no counting statistics, detection threshold, error bars, or surveyed areas are provided for Figs.2E-H, and each doping is represented by a single field of view. In addition, the hole concentrations p~0.05, 0.10, 0.15, and 0.19 are inferred from gap magnitudes via the calibration in ref. 33 rather than measured independently; if that calibration is uncertain, the claimed monotonic doping dependence is not robust. The statement that no correlation exists between FLC positions and interstitial oxygen locations is also unsupported by any correlation analysis. Please provide quantitative FLC areal densities, a defined FLC detection criterion, and an independent doping measure.","section":"Evolution of FLC charge state with increasing holes doping (Fig.2)"},{"comment":"The manipulation result is degenerate with surface atomic rearrangement. Figs.3D-F show clear motion of Bi atoms in the dashed boxes after applying biases of 2.2 to 4.0 V, and the text itself attributes the current jump to manipulation of 'charge carrier and surface atoms below the tip.' Therefore, the disappearance and reappearance of the FLC pattern in Figs.3G-I cannot be uniquely attributed to local electric-field doping of the CuO2 planes; a change in tip apex state or surface reconstruction could equally explain the dI/dV maps. The statement that 'the tip remained highly stable' is not supported by any control, such as repeated topography of a region far from the pulse site or tip spectroscopy before and after. A control separating electronic from topographic effects is required.","section":"Atomic manipulation of FLC charge state (Fig.3D-F)"},{"comment":"The proposed explanation that positive (negative) bias creates a nanoscale hole-enriched (hole-depleted) region is an assumption without local evidence. The changes in Δ(r) and superfluid-density maps in Figs.4D-I could be consequences of the same surface or tip-state modifications noted above; no independent measurement of local carrier concentration is provided, and the toy model in Figs.4J-L is not quantitatively constrained. As written, the model is a plausible narrative rather than a tested mechanism.","section":"Tip-electric field manipulation and toy model (Fig.4J-L)"},{"comment":"The claim that the 2a0 FLC is 'the smallest precursor unit for incoherent Cooper pairs' is an interpretation that is not tested by any pairing-sensitive measurement. The manuscript presents only single-particle dI/dV maps and spectra, with no phase-sensitive probe, Josephson STM, or comparison to a calculated pairing wavefunction. This does not invalidate the data, but the claim should be clearly labeled as a hypothesis, and the abstract's 'precursor states of pairing' framing should be moderated accordingly.","section":"Discussion and outlook"}],"minor_comments":[{"comment":"The abstract describes a characteristic 'kink' around 16 meV, while the main text and Fig.1I show a peak in the dI/dV spectra; please use consistent terminology for this spectral feature.","section":"Abstract and Fig.1I"},{"comment":"The text says a large current jump occurred '(see Fig.3D)', but the current-versus-time data are in Fig.3C; the cross-reference should be corrected.","section":"Fig.3C and text"},{"comment":"The caption lists two pseudogap values and two superconducting gap values for four samples; specify which gap values correspond to each of the four dopings.","section":"Fig.1C caption"},{"comment":"The text refers to interstitial oxygen maps as '(Fig.2 E to H)', but the oxygen dI/dV maps appear to be in Fig.2I-L; the cross-reference is inconsistent.","section":"Oxygen mapping paragraph"},{"comment":"The FLC extent is described as 2a0 in the Fig.3 caption but as having a lobe separation of approximately a0 in Fig.1; please define unambiguously whether 2a0 is the full clover diameter or the Cu-Cu separation.","section":"Fig.1H and Fig.3 caption"},{"comment":"The symbol Vs is used without definition, and the set-point current is given as 120 pA in the text but 115 pA in the Fig.3C caption; please make these consistent.","section":"Fig.3C"},{"comment":"The caption contains a doubled article ('the the crystal structure'); this is a typo.","section":"Fig.1B inset"},{"comment":"Ref. 34, used for comparison with a 400-meV FLC state, is an arXiv preprint; if this comparison is important, a published reference or a more detailed description of the energy scale and measurement conditions is needed.","section":"Ref. 34"},{"comment":"Several panels lack visible scale bars, and the phrase 'large-scale dI/dV mapping' in Fig.2H is not quantified; adding scale bars and stating the surveyed area would help the reader judge the vanishing claim.","section":"Figs.2E-H and 4G-I"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague — the interesting thing here is the claim of a 2a0 four-leaf clover pattern in dI/dV at 16 meV in underdoped Bi-2212, distinct from the ~400 meV FLC of ref. 34 and from stripes/checkerboards. If real, it's a new low-energy electronic texture that fades with doping and can be locally erased/restored by the tip. That would be worth chasing.\n\nWhat the paper does well: the phase diagram frame, the clear separation from previous FLC work, and the observation that the pattern disappears on the overdoped side. The authors also put impurity checks in the supplement (Fig S1/S2), which shows awareness of the obvious confound.\n\nThe soft spots are the load-bearing ones. The central attribution—that g(r,16 meV) reflects an intrinsic CuO2-plane electronic state—is not yet established. The main-text maps are representative, without line traces, template counts, or direct comparison to simultaneously acquired topography; that leaves standard z-feedback cross-talk on the table. The impurity controls are not analyzed in the main text, so the reader can't evaluate them without hunting in the supplement. More seriously, the manipulation experiment in Fig.3 shows clear Bi atom movement at the same voltages (2.2–4.0 V), so the disappearance/reappearance of FLC contrast is degenerate with surface reconstruction or tip apex changes. No control separates local electric-field doping from atomic rearrangement. The doping dependence rests on p values inferred from gap magnitudes rather than measured independently.\n\nThese aren't quibbles; the Cooper-pair precursor and 'tunable electronic phase' language in the abstract goes beyond what the shown data support. But the observation could still be genuine, and the paper deserves a serious referee. I'd want the revision to include quantified FLC statistics, topographic cross-checks, a control where the tip is pulsed away from the FLC, and some estimate of how field-induced doping could produce the gap and superfluid changes.\n\nNet: a candidate observation with a strong claim attached, currently under-supported. Worth sending to peer review, but not something I'd cite yet.","headline":"A genuinely new low-energy FLC texture in Bi-2212, but the paper hasn't yet shown it's an intrinsic CuO2 state, and the manipulation is entangled with surface atom motion.","tokens_in":7854,"tokens_out":2033,"would_cite":false,"duration_ms":21406,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A four-leaf clover-shaped electronic state found in underdoped cuprates is proposed as the smallest precursor unit of incoherent Cooper pairs.","keywords":["scanning tunneling microscopy","cuprate superconductors","Bi-2212","four-leaf clover state","electronic order","pseudogap","Cooper pair precursor","electric-field manipulation"],"falsifier":"A decisive check would be to acquire the 16 meV conductance map and the topographic image in the same field of view, align them pixel by pixel, and compute the cross-correlation between the FLC lobe positions and the corrugation maxima; if the FLC signal tracks the known BiO supermodulation or the atomic lattice corrugation, the intrinsic-electronic-state claim is falsified. The same comparison repeated with a different tip apex or after a controlled tip change would show whether the pattern is tip-dependent.","tokens_in":6791,"feed_emoji":"🍀","tokens_out":5625,"duration_ms":60964,"temperature":0.7,"pith_summary":"The paper claims that scanning tunneling microscopy resolves a previously unseen low-energy electronic state in the CuO2 planes of underdoped Bi-2212: a four-leaf clover-shaped pattern, about two lattice constants across, centered on copper sites and extending along the Cu-O bonds. The pattern shows up in conductance maps at 16 meV with a matching kink in the local spectra, becomes rarer as hole doping increases, and is absent in overdoped samples. The authors further show that a strong electric field from the STM tip can locally erase the pattern and a reversed field can restore it elsewhere. They interpret this state as the smallest real-space unit from which incoherent Cooper pairs would form in the pseudogap regime. A sympathetic reader should care because it proposes a concrete, locally manipulable electronic building block for pairing physics that has so far been discussed only at larger length scales.","feed_headline":"Four-leaf clover state may seed Cooper pairs in cuprates","feed_subtitle":"STM shows a 2a0 pattern at 16 meV that doping erases and an electric field can toggle.","key_machinery":"The carrying object is the four-leaf clover (FLC) electronic state itself, detected through spatially resolved differential conductance mapping g(r,16 meV) and corroborated by local dI/dV spectra that show a peak near 16 meV at the petal positions but not at the Cu center. The doping series from p~0.05 to p~0.19 provides the control axis, and the tip-induced electric field provides a local perturbation that reversibly modifies the state while the same field of view is imaged. The accompanying toy model ties the state's stability to a potential well created by weak Coulomb screening in the antiferromagnetic Mott background, which a local electric field can deepen or destroy.","core_discovery":"The central discovery is the existence of a 2a0 four-leaf clover-shaped electronic state at low energy in heavily underdoped Bi-2212, visible in dI/dV maps at 16 meV. The state is centered at a Cu site, has petals separated by roughly a0, and appears as an isolated island rather than a long-range ordered pattern. Its abundance falls with hole doping and it disappears in the overdoped regime. Using the STM tip as a local electric-field source, the authors show that the state can be erased with a positive bias above 2.2 V and re-emerges in a shifted position after a negative bias near 4.0 V, with local superconducting gap and superfluid density maps changing in the same region. They propose that the FLC state is the smallest precursor unit for incoherent Cooper pairs, distinct from the larger stripe and checkerboard patterns.","pith_inferences":["If the FLC state is generic to underdoped cuprates, it should also appear in other Bi-based or single-layer cuprate families; searching for it in a second compound would test the proposed universality.","The 16 meV energy scale and the local erasure could be used to write and erase superconducting regions, suggesting a route toward atomic-scale electronic devices based on local pairing texture.","The authors' identification of the FLC as a precursor is suggestive but not directly proven; a direct test would be to measure the local pair density or Josephson response at a single FLC site, which is not yet available."],"forward_implications":["If the FLC state is the precursor unit of incoherent Cooper pairs, then the pseudogap regime contains a real-space electronic structure at the 2a0 scale that precedes phase-coherent superconductivity.","The observed doping dependence provides a microscopic criterion: any complete theory of cuprate pairing must explain why this state exists only on the underdoped side and disappears before optimal doping.","The electric-field manipulation implies that local superconducting properties, including the gap and superfluid density, can be modified at the atomic scale in a reversible way.","The distinction drawn from 4a0 stripe and checkerboard orders suggests a hierarchy of electronic textures, with the FLC as the smallest member, so future work should look for the FLC at the boundaries or inside other ordered regions."],"supporting_citations":[{"why":"Supplies the justification that the cleaved BiO surface electronic structure reflects bulk CuO2 properties, the premise for reading the FLC state as intrinsic.","marker":"(31,32)"},{"why":"Previous observation of a four-leaf clover pattern at ~400 meV, used to distinguish the new low-energy FLC state.","marker":"(34)"},{"why":"Impurity-state scattering theory used to argue that the g(r,-16 meV) and g(r,0 meV) maps exclude impurity states.","marker":"(35)"},{"why":"Provides the doping calibration and gap assignments for the four samples studied.","marker":"(33)"},{"why":"Maps interstitial oxygen distribution, used to show no direct correlation between FLC locations and oxygen dopants.","marker":"(36)"},{"why":"Supplies the context of local Cooper pair units, against which the FLC is interpreted as the smallest precursor.","marker":"(40)"},{"why":"Previous observation of electronic cluster glass and asymmetry of tunneling currents, which motivates the low-energy search.","marker":"(16)"}],"fun_headline_variants":["Electric field toggles four-leaf clover state in cuprates","2a0 clover state at 16 meV vanishes with doping","STM probe manipulates clover state locally in cuprates","Cuprate clover state responds to doping and voltage"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the four-leaf clover contrast in the conductance maps is an intrinsic electronic state of the CuO2 planes, not a tip artifact, a BiO surface effect, or a topographic corrugation.","fun_headline_variants_meta":{"raw":{"variants":["Electric field toggles four-leaf clover state in cuprates","2a0 clover state at 16 meV vanishes with doping","STM probe manipulates clover state locally in cuprates","Cuprate clover state responds to doping and voltage"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000663,"raw_usage":{"total_tokens":2996,"prompt_tokens":879,"completion_tokens":2117,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":495,"completion_tokens_details":{"reasoning_tokens":2043}},"tokens_in":495,"tokens_out":2117,"duration_ms":18456,"temperature":1.0,"reasoning_tokens":2043,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T22:25:30.550922+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A decisive check would be to acquire the 16 meV conductance map and the topographic image in the same field of view, align them pixel by pixel, and compute the cross-correlation between the FLC lobe positions and the corrugation maxima; if the FLC signal tracks the known BiO supermodulation or the atomic lattice corrugation, the intrinsic-electronic-state claim is falsified. The same comparison repeated with a different tip apex or after a controlled tip change would show whether the pattern is tip-dependent.","supporting_citations":[],"review_version":1}