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arxiv: 2511.00920 · v2 · submitted 2025-11-02 · ❄️ cond-mat.supr-con · cond-mat.mes-hall

Point-contact enhanced superconductivity in trigonal PtBi2: quest for the origin of high-Tc

O. E. Kvitnitskaya , L. Harnagea , G. Shipunov , S. Aswartham , I. Kovalchuk , V. V. Fisun , D. V. Efremov , B. B\"uchner
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Yu. G. Naidyuk
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Pith reviewed 2026-05-18 01:04 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con cond-mat.mes-hall
keywords point-contact superconductivityPtBi2Weyl semimetalenhanced critical temperaturestrain-induced superconductivitytopological superconductivityferromagnetic tips
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The pith

Point contacts on trigonal PtBi2 raise superconducting Tc up to 8 K, several times above bulk values, through local strain.

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

The paper investigates enhanced superconductivity in point contacts formed on the type-I Weyl semimetal trigonal t-PtBi2. Using tips of normal metals and ferromagnets, the authors measure differential resistance and find Tc values mostly between 3 and 5 K, with some contacts reaching 8 K. The critical magnetic field also increases substantially to several Tesla. The enhancement appears more pronounced at the edges of sample flakes than on flat surfaces. The authors link the rise in Tc to pressure or strain created when the point contact is made and note that t-PtBi2 may thereby become suitable for topological superconductivity at higher temperatures.

Core claim

Point contacts on trigonal t-PtBi2 exhibit enhanced superconductivity with Tc typically between 3 and 5 K and reaching as high as 8 K when formed with either normal-metal or ferromagnetic tips. The critical magnetic field is likewise enhanced to several Tesla. Contacts made at the edges of flakes show greater Tc increases than those on the platelet plane. The authors propose that the common origin of the enhancement is the pressure or strain generated during point-contact formation. These findings position t-PtBi2 as a candidate for realizing topological superconductivity at more accessible temperatures.

What carries the argument

Local pressure or strain induced at the point-contact interface, which raises the superconducting critical temperature and critical field in the Weyl semimetal t-PtBi2.

If this is right

  • The Tc enhancement persists with ferromagnetic tips, indicating a potentially complex interplay between the superconducting state and magnetism.
  • Contacts at flake edges produce larger Tc gains than those on flat surfaces, pointing to a role for boundaries or reduced dimensionality.
  • The critical magnetic field reaches several Tesla, extending the range of accessible superconducting states.
  • t-PtBi2 may support topological superconductivity at temperatures up to 8 K rather than the lower bulk values.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If strain is the dominant mechanism, controlled hydrostatic pressure experiments on bulk crystals could test whether the same Tc gains occur without forming point contacts.
  • The compatibility with ferromagnetic tips suggests experiments that combine the enhanced superconductivity with proximity-induced magnetism to probe possible topological features.
  • The edge preference implies that lithographically defined nanostructures or thin flakes might systematically amplify the effect for device applications.

Load-bearing premise

The rise in Tc is caused primarily by mechanical pressure or strain from point-contact formation rather than by interface chemistry, tip-induced doping, or other local effects.

What would settle it

Direct local strain mapping at the contact that shows negligible strain while Tc remains enhanced, or failure to observe comparable Tc increases in bulk samples under equivalent external pressure.

Figures

Figures reproduced from arXiv: 2511.00920 by B. B\"uchner, D. V. Efremov, G. Shipunov, I. Kovalchuk, L. Harnagea, O. E. Kvitnitskaya, S. Aswartham, V. V. Fisun, Yu. G. Naidyuk.

Figure 1
Figure 1. Figure 1: Temperature variation of dV/dI of PtBi2 – Ni PC with resistance R=5.4 Ω. The left inset shows the current-voltage I(V) curve in normal (dashed red) and superconducting state (solid black). The upper inset shows the calculated static PC resistance V/I at 1.5K. Bottom inset on the right shows behavior of residual superconducting minimum as PC approaches the normal state. Results [PITH_FULL_IMAGE:figures/ful… view at source ↗
Figure 4
Figure 4. Figure 4: demonstrates the typical temperature and magnetic field behavior of dV/dI for PtBi2 homocontacts. In general, its shape is similar to the case of heterocontacts. Note that there is no supercurrent (critical current) at V=0, and PC has a nonzero resistance, that is, PC is only partially in a superconducting state. So far, it looks typical for enhanced superconductivity, e.g., the same nonzero resistance we … view at source ↗
Figure 6
Figure 6. Figure 6: Temperature variation of dV/dI of PtBi2 “soft” PC with resistance R=1.4 Ω in the normal state. Left inset shows dV/dI in the extended voltage range at T=1.9K. The right inset shows the dV/dI behavior in a magnetic field at T = 1.9 K [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
read the original abstract

We studied enhanced superconductivity in point contacts (PCs) based on a type-I Weyl semimetal trigonal t-PtBi2 using both normal metal (Ag, Cu, Pt) and ferromagnetic (Fe, Co, Ni) tips by measuring the differential resistance dV/dI(V) curves. In most cases, the value of the superconducting critical temperature Tc ranges between 3 and 5 K, which is several times higher than the maximum bulk Tc. Notably, among the various PCs we examined, a few achieved Tc values as high as 8 K, including those with both normal and ferromagnetic tips. Additionally, the critical magnetic field is also highly enhanced in these PCs and reaches up to several Tesla. The common reason for the Tc increase may be related to pressure/strain caused during the PC's formation. It is worth noting that a greater increase in Tc is observed in PCs formed at the edge of the sample flake, compared to those formed on the plane of the platelet. The results also reveal that the enhancement of Tc in PCs based on t-PtBi2 is compatible with ferromagnetic tip, which may suggest a potentially complex nature of enhanced superconductivity. Our findings besides suggest that t-PtBi2 is a promising candidate for realizing topological superconductivity at more accessible temperatures.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 3 minor

Summary. The manuscript reports experimental point-contact spectroscopy measurements on trigonal PtBi2 (a type-I Weyl semimetal) using normal-metal (Ag, Cu, Pt) and ferromagnetic (Fe, Co, Ni) tips. Differential resistance dV/dI(V) curves show enhanced superconducting critical temperatures Tc typically in the 3–5 K range and up to 8 K in select contacts—several times higher than the maximum bulk Tc—together with critical magnetic fields reaching several Tesla. The authors attribute the enhancement primarily to pressure/strain induced during point-contact formation, noting larger effects for edge contacts than planar ones, and observe that the enhancement persists with ferromagnetic tips. The work positions t-PtBi2 as a candidate for realizing topological superconductivity at higher temperatures.

Significance. If the reported Tc enhancement can be reproducibly linked to controlled strain and distinguished from interface or doping effects, the results would provide a practical route to elevate the superconducting transition temperature in topological semimetals, thereby enabling more accessible studies of topological superconductivity. The compatibility with ferromagnetic tips introduces an additional degree of freedom that may illuminate the interplay between magnetism and superconductivity in this material. The raw dV/dI data constitute concrete experimental evidence for the elevated Tc and Hc values.

major comments (3)
  1. [Abstract] Abstract and discussion: the central claim that pressure/strain induced by point-contact formation is the common reason for the Tc increase (3–8 K) is stated without direct local strain quantification, Raman/XRD mapping of the contact region, or comparison to bulk t-PtBi2 under calibrated uniaxial or hydrostatic pressure. Alternative mechanisms (interface chemistry, tip-induced doping, or disorder) are mentioned only qualitatively and not excluded by control experiments.
  2. [Results] Results section (edge vs. planar contacts): the statement that a greater Tc increase occurs at the edges of the sample flake compared with the plane is presented qualitatively. No statistical distribution, average enhancement factors, or error bars on the Tc values for the two geometries are provided, weakening the support for a strain-based interpretation.
  3. [Methods] Methods/Results: the procedure for extracting Tc and the upper critical field from the dV/dI(V) curves is not described in sufficient detail (e.g., criterion for the onset of zero resistance or field dependence), making it difficult to assess the robustness of the reported enhancements up to 8 K and several Tesla.
minor comments (3)
  1. [Abstract] The exact numerical value of the maximum bulk Tc for t-PtBi2 should be stated explicitly in the abstract and introduction for direct comparison with the point-contact values.
  2. [Figures] Figure captions and text should clarify the tip-sample contact resistance range and the criteria used to identify the superconducting transition in the presence of possible Andreev reflection or other spectroscopic features.
  3. [Discussion] A brief discussion of possible surface reconstruction or oxidation effects on the PtBi2 flakes prior to contact formation would improve reproducibility.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comments. We respond to each major point below, indicating where revisions will be made to improve clarity and support for our interpretations.

read point-by-point responses

  1. Referee: [Abstract] Abstract and discussion: the central claim that pressure/strain induced by point-contact formation is the common reason for the Tc increase (3–8 K) is stated without direct local strain quantification, Raman/XRD mapping of the contact region, or comparison to bulk t-PtBi2 under calibrated uniaxial or hydrostatic pressure. Alternative mechanisms (interface chemistry, tip-induced doping, or disorder) are mentioned only qualitatively and not excluded by control experiments.

    Authors: We agree that the manuscript does not include direct local strain measurements such as Raman or XRD mapping of the contact region, nor a direct comparison of our point-contact results to bulk t-PtBi2 under calibrated pressure. The strain interpretation is inferred from the systematic difference in enhancement between edge and planar contacts together with the use of multiple tip materials. We have expanded the discussion to address alternative mechanisms (interface chemistry, doping, and disorder) in greater detail and to explain why they appear less consistent with the full data set. In the revised manuscript we will further moderate the language in the abstract and discussion to present strain as a plausible but not definitively proven origin, while noting the absence of direct quantification as a limitation. revision: partial

  2. Referee: [Results] Results section (edge vs. planar contacts): the statement that a greater Tc increase occurs at the edges of the sample flake compared with the plane is presented qualitatively. No statistical distribution, average enhancement factors, or error bars on the Tc values for the two geometries are provided, weakening the support for a strain-based interpretation.

    Authors: We accept that the edge-versus-planar comparison was presented only qualitatively. In the revised manuscript we will add a statistical summary of the Tc values, including mean enhancement factors, standard deviations, and error bars (or a histogram) separately for edge and planar contacts. This will be inserted into the Results section to provide quantitative support for the observed difference. revision: yes

  3. Referee: [Methods] Methods/Results: the procedure for extracting Tc and the upper critical field from the dV/dI(V) curves is not described in sufficient detail (e.g., criterion for the onset of zero resistance or field dependence), making it difficult to assess the robustness of the reported enhancements up to 8 K and several Tesla.

    Authors: We thank the referee for highlighting this omission. We will insert a dedicated paragraph in the Methods section that explicitly states the criteria used to extract Tc (e.g., the temperature at which dV/dI drops to 50 % of the normal-state value or the onset of zero resistance) and the procedure for determining the upper critical field from the field-dependent data. Any fitting routines or threshold definitions will also be specified. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental observations with no derivations or self-referential predictions

full rationale

The manuscript reports experimental dV/dI(V) measurements on point contacts formed with normal and ferromagnetic tips on trigonal t-PtBi2 flakes. Enhanced Tc (3–8 K) and critical fields are directly observed and compared to bulk values; the suggestion that pressure/strain during contact formation is responsible is offered qualitatively on the basis of edge-versus-plane differences. No equations, fitted parameters, predictions, or first-principles derivations appear that could reduce the reported Tc values to inputs by construction. No self-citation chains or uniqueness theorems are invoked to justify the central observations. The work is therefore self-contained against external benchmarks and receives the default non-circularity finding.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

This is an experimental condensed-matter study that relies on standard domain assumptions for interpreting point-contact data as superconductivity signatures; no free parameters, new entities, or ad-hoc axioms are introduced beyond routine measurement interpretation.

axioms (1)
  • domain assumption Differential resistance dV/dI(V) curves can be reliably interpreted to extract superconducting critical temperature Tc and critical magnetic field values.
    This is the standard interpretive framework in point-contact spectroscopy on superconductors.

pith-pipeline@v0.9.0 · 5822 in / 1433 out tokens · 85033 ms · 2026-05-18T01:04:45.010171+00:00 · methodology

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Reference graph

Works this paper leans on

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    -8 -4 0 4 8 0.9 1.0 125m Co wire to PtBi2 plane R=9  1.5K 2K 2.5K 3.3K 3.8K 4.2K 4.9K 6.2K 5.5K V (mV) dV/dI (rel

    Variety of dV/dI spectra of heterocontacts based on PtBi2. -8 -4 0 4 8 0.9 1.0 125m Co wire to PtBi2 plane R=9  1.5K 2K 2.5K 3.3K 3.8K 4.2K 4.9K 6.2K 5.5K V (mV) dV/dI (rel. un.) PtBi2- Co Tc 6.2K (a) -6 -4 -2 0 2 4 6 0.9 1.0 125m Fe wire to PtBi2 edge 10 , 0T 1.5K 2K 2.3K 2.7K 3K 3.5K 4K V (mV) dV/dI (rel. un.) PtBi2 - Fe Tc ~ 4K (b) -4 -2 0 2 41.00...

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    Let us try to estimate the size of PCs from the resistance RPC

    Estimation of the minimal PC size. Let us try to estimate the size of PCs from the resistance RPC. The latter is expressed by the well-known Wexler formula, which consists of the sum of ballistic Sharvin RSh and diffusive Maxwell resistance RM [23]: RPC = RSh + RM ≈16ρl/3πd2+ ρ/d, (1) here d is the PC diameter, ρ is the resistivity, l is the mean free pat...

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