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arxiv: 2606.17750 · v1 · pith:6EAQ6TZUnew · submitted 2026-06-16 · ❄️ cond-mat.supr-con

AC calorimetric study of magneto-quantum oscillations in anisotropic multiband V₂Ga₅ superconductor

Yevhen V. Petrenko , Jozef Ka\v{c}mar\v{c}\'ik , Tom\'a\v{s} Samuely , Jozef Hani\v{s} , Slavom\'ir Gab\'ani , Szymon Kr\'olak , Michal J. Winiarski , Tomasz Klimczuk
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Martin Gmitra Peter Samuely
This is my paper

Pith reviewed 2026-06-26 22:22 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con
keywords magneto-quantum oscillationsAC calorimetryFermi surfaceV2Ga5Berry fluxanisotropic superconductorhybridization phase twist
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The pith

AC calorimetry detects a single 126.6 T frequency that confirms the bulk elliptical γ Fermi-surface pocket in V₂Ga₅ and shows its net Berry flux stays constant under any field orientation.

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

The paper applies AC calorimetry to measure magneto-quantum oscillations in V₂Ga₅ single crystals and isolates one dominant frequency of 126.6 T through fast Fourier transform. This frequency matches the expected size and shape of the γ pocket near the Z point, establishing that the oscillations arise from the true bulk quasiparticle density of states rather than surface or minority-band contributions. Temperature and field dependence of the amplitudes yield the cyclotron mass, Dingle temperature, relaxation time, mobility, and mean free path for that pocket. The angular variation of the frequency follows the calculated anisotropy of the γ pocket, and the net Berry flux remains unchanged with field direction because a hybridization phase twist inside the pocket is conserved.

Core claim

A single dominant MQO frequency of 126.6 T resolved by FFT in AC-calorimetry data on V₂Ga₅ directly confirms the bulk origin of the elliptical γ Fermi-surface pocket near the Z point; its angular dependence reproduces the calculated anisotropy, while the net Berry flux stays invariant under field rotation owing to a conserved hybridization phase twist within the pocket.

What carries the argument

The γ Fermi-surface pocket together with its conserved hybridization phase twist that keeps net Berry flux orientation-independent.

If this is right

  • The method isolates bulk DOS oscillations without magnetization artifacts.
  • Precise values of cyclotron mass, Dingle temperature, quantum relaxation time, mobility, and mean free path follow directly from amplitude analysis.
  • Net Berry flux invariance holds for arbitrary field orientations because the phase twist inside the γ pocket is conserved.
  • AC calorimetry functions as a macroscopic probe of topological orbital hybridization in multiband intermetallics.

Where Pith is reading between the lines

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

  • The same AC-calorimetry approach could map Berry-phase properties in other anisotropic superconductors where magnetization signals are weak.
  • If the phase twist is conserved across related compounds, similar flux invariance might appear in any multiband system with hybridized pockets near high-symmetry points.
  • Testing the frequency under pressure or doping would check whether the γ pocket remains the dominant contributor when the superconducting transition temperature changes.

Load-bearing premise

The AC-calorimetry signal comes only from the oscillatory bulk quasiparticle density of states of the γ pocket, with negligible input from other bands or surface effects.

What would settle it

A de Haas–van Alphen measurement on the same crystals that yields a different dominant frequency or an angular dependence that deviates from the first-principles calculation after identical background handling.

Figures

Figures reproduced from arXiv: 2606.17750 by Jozef Hani\v{s}, Jozef Ka\v{c}mar\v{c}\'ik, Martin Gmitra, Michal J. Winiarski, Peter Samuely, Slavom\'ir Gab\'ani, Szymon Kr\'olak, Tomasz Klimczuk, Tom\'a\v{s} Samuely, Yevhen V. Petrenko.

Figure 1
Figure 1. Figure 1: a) Schematic view of the crystal structure of V2Ga5. Vanadium atoms are shown with red balls and Gallium atoms with green. The solid box shows one unit cell. b) Calculated Fermi surface with rendered V d-orbitals illustrating the γ pocket centered around the Z point [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Quantum oscillations in V2Ga5 single crystals derived from heat capacity (left axis) and magnetization (right axis). The corresponding color represents the orientation of the sample towards the applied field, blue – μ0H || c, red – μ0H || ab. The heat capacity MQO is measured at 0.73 K and magnetization MQO at 2 K [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The FFT spectra of the Cosc/T data at different temperatures and fields μ0H || c). The peak at 253.2 T represents the second harmonic of oscillations, negligible in further analysis. By applying the FFT frequency analysis to a field sweep between Bmin = 3 T and Bmax = 8 T at selected temperatures we resolve a sharp frequency peak F = 126.6 T with its second harmonic of lower intensity at 253.2 T, shown in … view at source ↗
Figure 4
Figure 4. Figure 4: |fT''(z)| – fit (red curve) to the FFT amplitude (black dots) for the effective mass determination. A thin black line is a guide for the eyes. Another approach is to exploit the fact that fT``(zC) = 0 at zC ≈ 1.606. It introduces a node in the amplitude of the oscillatory specific heat as a function of magnetic field, accompanied by a π-phase shift. Since the value of z depends only on the temperature, mag… view at source ↗
Figure 5
Figure 5. Figure 5: Averaging over the values obtained at different temperatures gives [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 5
Figure 5. Figure 5: Experimental Cosc/T (black curve, μ0H || c) directly fitted to the LK model (red curve) with the only main harmonic of 126.6 T at 2.00 K. The magenta vertical line denotes the node point location, while the blue one shows a position that corresponds to the average m* value, taking into account measurements at different temperatures. 4. Dingle temperature Another important parameter in the LK model is the D… view at source ↗
Figure 6
Figure 6. Figure 6: Experimental Cosc/T (black curve, μ0H || c) directly fitted (red curve) to the LK model with the only main harmonic of 126.6 T at 0.73 K. From TD the quantum relaxation time 2 BD kT   = = 0.98∙10-12 s and quantum mobility * e m  m = = 7010 cm2 /(V∙s) are calculated. From the free electron model, knowing the relation between F and the extremal area AF = πkF 2 (Eq. 5), we estimate the Fermi velocity * F F… view at source ↗
Figure 7
Figure 7. Figure 7: The Landau fan diagram constructed by minima of [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: The FFT spectra of the Cosc/T data when the external magnetic field is oriented towards the c axis at different angles (0.73 K). In [PITH_FULL_IMAGE:figures/full_fig_p010_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Experimental Cosc/T (black curve, μ0H || ab) directly fitted (red curve) to the LK model with the only main harmonic of 174.2 T at 0.73 K. As can be seen, the amplitude of the signal decreased almost threefold in comparison with that of Cosc(T = 0.73 K, B) at μ0H || c, while the main frequency increased to 174.2 T. The increase in frequency with angle indicates that the extremal Fermi-surface cross-section… view at source ↗
Figure 10
Figure 10. Figure 10: The angular dependences of the FFT amplitude (red dots) and frequency (blue dots). Angle increases from 0 for μ0H || c to 90 degrees for μ0H || ab. Calculated angular-dependent frequencies (green curve) corresponding to the extremal cross-section of the γ pocket. Discussion According to previous transport studies, V2Ga5 is a multiband metal containing both electron￾and hole-like carriers. Nevertheless, it… view at source ↗
read the original abstract

Unlike de Haas--van Alphen measurements, heat-capacity magneto-quantum oscillations directly probe the oscillatory bulk quasiparticle density of states. Here, we report the observation of MQOs in V$_2$Ga$_5$ single crystals studied via highly sensitive ac calorimetry. The strongest MQO signal is observed for a magnetic field applied along the vanadium chains, in excellent agreement with de Haas--van Alphen magnetization data. A single dominant frequency of 126.6 T resolved by fast Fourier transform confirms the true bulk origin of the elliptical $\gamma$ Fermi-surface pocket located near the Z point of the Brillouin zone. The angular dependence of the FFT frequency closely tracks the anisotropy of the $\gamma$ pocket, as supported by first-principles calculations. Analysis of the temperature- and field-dependent MQO amplitudes allows the precise determination of the effective cyclotron mass, Dingle temperature, quantum relaxation time, carrier mobility, and electron mean free path. Furthermore, we demonstrate that the net Berry flux is invariant with respect to the magnetic-field orientation, as a consequence of a conserved hybridization phase twist within the $\gamma$ pocket. These findings establish ac calorimetry as a powerful macroscopic probe of topological orbital hybridization in complex intermetallics.

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

2 major / 0 minor

Summary. The manuscript reports AC-calorimetric detection of magneto-quantum oscillations (MQOs) in V₂Ga₅ single crystals. A single dominant FFT frequency of 126.6 T is identified and assigned to the elliptical γ Fermi-surface pocket near Z; its angular dependence is said to track the pocket anisotropy from DFT. Amplitude analysis versus temperature and field yields the cyclotron mass, Dingle temperature, quantum relaxation time, mobility, and mean free path. The net Berry flux is claimed to be invariant under field reorientation because of a conserved hybridization phase twist inside the γ pocket. The work positions AC calorimetry as a bulk probe of topological orbital hybridization in multiband superconductors.

Significance. If the single-frequency exclusivity and Berry-flux invariance are rigorously established, the result would provide a macroscopic, bulk-sensitive route to orbital-hybridization topology that complements dHvA, with potential relevance to other anisotropic intermetallic superconductors. The parameter extraction (mass, Dingle temperature, mobility) would be a useful addition to the literature on V₂Ga₅.

major comments (2)
  1. [abstract] Abstract (FFT paragraph): the assertion that observation of a single dominant frequency of 126.6 T 'confirms the true bulk origin' of the γ pocket is load-bearing for the central claim yet rests on the unverified premise that other bands and surface/vortex contributions lie below noise after background removal. The manuscript must supply the raw C_ac(H) traces, explicit background-subtraction protocol, window functions, and quantitative multi-frequency fit residuals to demonstrate that no additional frequencies exceed the noise floor.
  2. [Berry flux discussion] Berry-flux section: the statement that net Berry flux is invariant 'as a consequence of a conserved hybridization phase twist within the γ pocket' is presented without an explicit derivation linking the observed frequency anisotropy to a field-independent flux value. If this invariance is a key result, the manuscript must show the flux calculation (e.g., via Lifshitz–Kosevich amplitude or Onsager relation) and demonstrate that the phase-twist constraint follows directly from the data rather than from an additional model assumption.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for the constructive comments, which will help strengthen the presentation of our AC calorimetry results on V₂Ga₅. We address each major comment below.

read point-by-point responses

  1. Referee: [abstract] Abstract (FFT paragraph): the assertion that observation of a single dominant frequency of 126.6 T 'confirms the true bulk origin' of the γ pocket is load-bearing for the central claim yet rests on the unverified premise that other bands and surface/vortex contributions lie below noise after background removal. The manuscript must supply the raw C_ac(H) traces, explicit background-subtraction protocol, window functions, and quantitative multi-frequency fit residuals to demonstrate that no additional frequencies exceed the noise floor.

    Authors: We agree that additional documentation of the data processing is needed to rigorously support the single-frequency claim. In the revised manuscript we will add the raw C_ac(H) traces to the supplementary information, provide an explicit description of the background-subtraction protocol, specify the window functions used for the FFT, and include quantitative residuals from multi-frequency fits demonstrating that no secondary frequencies exceed the noise floor. revision: yes

  2. Referee: [Berry flux discussion] Berry-flux section: the statement that net Berry flux is invariant 'as a consequence of a conserved hybridization phase twist within the γ pocket' is presented without an explicit derivation linking the observed frequency anisotropy to a field-independent flux value. If this invariance is a key result, the manuscript must show the flux calculation (e.g., via Lifshitz–Kosevich amplitude or Onsager relation) and demonstrate that the phase-twist constraint follows directly from the data rather than from an additional model assumption.

    Authors: The invariance follows from the Onsager relation applied to the measured frequency anisotropy, which reproduces the DFT-predicted elliptical cross-section of the γ pocket; the hybridization phase twist remains orientation-independent because the topological orbital character is intrinsic to the pocket. We acknowledge that an explicit step-by-step derivation was not included in the main text. In revision we will add a supplementary section containing the flux calculation (via Onsager relation and Lifshitz–Kosevich amplitude analysis) and show that the phase-twist constraint is directly implied by the data together with the DFT band structure, without further model assumptions. revision: yes

Circularity Check

0 steps flagged

No significant circularity; claims rest on independent experimental FFT data and external first-principles comparisons

full rationale

The abstract and provided text contain no equations, self-citations, or derivations that reduce a claimed result to its own inputs by construction. The single dominant 126.6 T frequency is presented as direct experimental confirmation of the γ-pocket bulk origin via comparison to dHvA data; angular dependence is stated to track anisotropy 'as supported by first-principles calculations' (external benchmark). The Berry-flux invariance is asserted as a demonstrated consequence of a conserved hybridization phase twist, but no reduction to a fitted parameter, self-defined quantity, or load-bearing self-citation is quoted or exhibited. No ansatz smuggling, renaming of known results, or uniqueness theorems imported from the same authors appear. The derivation chain is therefore self-contained against external benchmarks (dHvA, band-structure calculations) with no circular steps meeting the strict quotation-and-reduction criteria.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claims rest on the assumption that AC calorimetry directly measures the oscillatory bulk density of states and that the single FFT peak can be unambiguously assigned to the γ pocket whose anisotropy and Berry properties are taken from first-principles calculations; no new entities are postulated.

free parameters (1)
  • FFT frequency = 126.6 T
    126.6 T extracted from the oscillatory signal; used to identify the γ pocket size.
axioms (2)
  • domain assumption AC calorimetry signal is proportional to the oscillatory quasiparticle density of states without significant non-bulk contributions.
    Stated in the opening sentence of the abstract as the motivation for using heat-capacity MQOs versus dHvA.
  • domain assumption The angular dependence of the observed frequency directly reflects the intrinsic ellipticity of the γ pocket.
    Invoked when the abstract states that the angular dependence closely tracks the anisotropy supported by first-principles calculations.

pith-pipeline@v0.9.1-grok · 5824 in / 1765 out tokens · 34117 ms · 2026-06-26T22:22:59.167923+00:00 · methodology

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Reference graph

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