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arxiv: 2605.29985 · v1 · pith:XNWTXALYnew · submitted 2026-05-28 · ❄️ cond-mat.supr-con · cond-mat.mtrl-sci

Stability Analysis of Superconductivity in textit{P6/mmm}-LaSc₂H₂₄ and its Experimental Reproducibility from La-Sc Alloys

Dmitrii V. Semenok , Ivan A. Troyan , Di Zhou , Emil A. Yuzbashyan , Boris L. Altshuler , Viktor V. Struzhkin This is my paper

Pith reviewed 2026-06-29 00:26 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con cond-mat.mtrl-sci
keywords LaSc2H24high-pressure hydridessuperconductivityelectron-phonon couplingstability analysissynthesis reproducibility
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The pith

Tetrahedral electron-phonon integration yields Tc above 300 K for LaSc2H24 at 300 GPa while the phase sits at the stability edge.

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

The paper examines room-temperature superconductivity in the lanthanum-scandium hydride P6/mmm-LaSc2H24. It shows that σ-broadening of the double delta-function at the Fermi surface produces Tc values that depend strongly on the arbitrary broadening parameter, whereas the tetrahedral method for the electron-phonon interaction removes this dependence and returns Tc greater than 300 K at 300 GPa. Stability analysis finds the compound at the boundary of the metallic state with ξ equal to 0.54 in the 250-300 GPa interval, comparable to the position of fcc-LaH10 at lower pressures. High-pressure experiments starting from a (La, Sc2) alloy at 250-280 GPa produce no superconducting La-Sc-H phases between 245 K and 300 K. The authors identify simultaneous deposition of the metals as a possible requirement for forming the target compound.

Core claim

The tetrahedral method for the electron-phonon interaction, unlike σ-broadening of the double delta function, produces a stable Tc > 300 K at 300 GPa for LaSc2H24. This compound exists at the edge of stability (ξ = 0.54) in the 250-300 GPa range. Experimental synthesis from the (La, Sc2) alloy at 250-280 GPa produces no superconducting La-Sc-H phases.

What carries the argument

The tetrahedral method for evaluating the electron-phonon coupling matrix elements on the Fermi surface.

Load-bearing premise

Unsuccessful attempts to synthesize LaSc2H24 from the (La,Sc2) alloy indicate that the compound does not form at all, rather than that the chosen pressure, temperature, or precursor method was insufficient.

What would settle it

Detection of superconductivity above 245 K or formation of the P6/mmm-LaSc2H24 phase in samples prepared by simultaneous deposition of lanthanum and scandium metals at 250-280 GPa.

Figures

Figures reproduced from arXiv: 2605.29985 by Boris L. Altshuler, Di Zhou, Dmitrii V. Semenok, Emil A. Yuzbashyan, Ivan A. Troyan, Viktor V. Struzhkin.

Figure 1
Figure 1. Figure 1: Qualitative mechanism of possible instability of the metallic hydrogen sublattice in superhydrides during decompression. (A) Experimental picture of hydride decompression with an increase in the critical temperature, sample resistance, electron-phonon interaction parameter, and, eventually, disappearance of superconductivity. The color scale corresponds to the transition from low (blue) to high (red) value… view at source ↗
Figure 2
Figure 2. Figure 2: Metallic state stability and superconducting properties of P6/mmm-LaSc2H24 under pressure. (A) Temperature￾dependent stability criterion ξ(T) for LaSc2H24 in harmonic approximation (HA) at 290-350 GPa, showing possible violation of the stability criterion (ξ > 0.5) with the maximum ξmax = 0.55 at 290 GPa. “σ” corresponds to calculations using formula (3), and “tetra” corresponds to the tetrahedral method o… view at source ↗
Figure 3
Figure 3. Figure 3: Harmonic Eliashberg functions and superconducting state parameters for isostructural (A) P6/mmm-La3H24, (B) Sc3H24, and (E) LaSc2H24 at 300 GPa in harmonic approximation. The tetrahedral method was used for Quantum Espresso calculations with a k-mesh of 12×12×12, a q-mesh of 4×4×4, and for the electron band structure calculations, we applied a [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Synthesis of (La,Sc)Hx using infrared pulsed laser heating (LH) under high pressure in DAC SL-1. (A-C) Optical micrographs showing the sample chamber and electrical contacts before and after laser heating at high pressure. (A) Initial picture of the (La,Sc)/AB (ammonia borane) sample before LH. (B) State after LH showing a blackening of the sample’s surface. (C) View of sample after LH, highlighting the re… view at source ↗
Figure 5
Figure 5. Figure 5: Synthesis of (La,Sc)Hx using infrared pulsed laser heating (LH) under high pressure in DAC SL-2. (a, b) Optical micrographs showing the sample chamber and electrical contacts before (A) and after (B) laser heating at high pressure. After LH we can see a blackening of the sample’s surface. (C, D) Raman spectra collected before and after laser synthesis in (C) the region of the diamond Raman edge, and in (D)… view at source ↗
read the original abstract

In this work, we analyze the feasibility of room-temperature superconductivity in the lanthanum-scandium hydride $\textit{P6/mmm}$-LaSc$_2$H$_{24}$. We demonstrate that the electron-phonon coupling calculations performed using the ${\sigma}$-broadening of the double ${\delta}$-function at the Fermi surface lead to a very strong dependence of $\textit{T$_c$}({\sigma})$ on the arbitrary ${\sigma}$, whereas the tetrahedral method for the electron-phonon interaction is free from this drawback and leads to $\textit{T$_c$}$ > 300 K at 300 GPa in agreement with previous predictions. By analyzing the stability of the metallic state of LaSc$_2$H$_{24}$ at 250-300 GPa, we show that this compound is at the edge of the stability region (${\xi}$ = 0.54), similar to $\textit{fcc}$ LaH$_{10}$ at 140-150 GPa. Experimental attempts to synthesize LaSc$_2$H$_{24}$ at 250-280 GPa starting from the (La,Sc$_2$) alloy are unsuccessful and indicate the absence of even traces of superconductivity at 245-300 K in all the resulting La-Sc-H hydrides. The method for preparing the precursor by simultaneous deposition of La and Sc metals may be a key factor for the successful synthesis of LaSc$_2$H$_{24}$.

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 / 2 minor

Summary. The manuscript analyzes the feasibility of room-temperature superconductivity in P6/mmm-LaSc₂H₂₄. It demonstrates that σ-broadening of the double δ-function at the Fermi surface produces strong, arbitrary dependence of Tc(σ), whereas the tetrahedral method for electron-phonon coupling yields Tc > 300 K at 300 GPa. Stability analysis places the compound at the edge of the metallic state (ξ = 0.54) at 250-300 GPa, analogous to fcc-LaH₁₀. Experimental attempts to form the phase from (La,Sc₂) alloy at 250-280 GPa are reported as unsuccessful, with no superconductivity observed at 245-300 K, and simultaneous La/Sc deposition is suggested as potentially key.

Significance. If the tetrahedral-method results and stability assessment are robust, the work would supply a concrete methodological caution against σ-broadening in hydride calculations and illustrate the experimental difficulties for phases near stability boundaries. The failed synthesis attempts supply independent evidence separate from the theoretical Tc values.

major comments (2)
  1. [Abstract] Abstract (experimental paragraph): the claim that unsuccessful synthesis from the (La,Sc₂) alloy indicates absence of LaSc₂H₂₄ formation is load-bearing for the reproducibility conclusion, yet the text itself states that simultaneous deposition 'may be a key factor,' leaving open the possibility that the alloy-precursor route fails even if the phase is stable under improved conditions; no controls with known analogs or direct phase identification are described to close this gap.
  2. [Stability analysis] Stability analysis (ξ = 0.54): the quantitative definition of the stability parameter ξ, the pressure range over which it is evaluated, and the explicit numerical comparison to the corresponding value for LaH₁₀ at 140-150 GPa are not provided in sufficient detail to confirm that the compound sits at a comparable stability edge; this underpins the central claim linking marginal stability to synthesis difficulty.
minor comments (2)
  1. The abstract refers to 'all the resulting La-Sc-H hydrides' without specifying the characterization techniques, pressure calibration, or temperature range of the resistivity or magnetic measurements.
  2. Notation for the stability parameter ξ should be introduced with its explicit formula or reference in the main text.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and constructive comments on our manuscript. We address each major comment point by point below, indicating where revisions will be made to improve clarity and precision.

read point-by-point responses

  1. Referee: [Abstract] Abstract (experimental paragraph): the claim that unsuccessful synthesis from the (La,Sc₂) alloy indicates absence of LaSc₂H₂₄ formation is load-bearing for the reproducibility conclusion, yet the text itself states that simultaneous deposition 'may be a key factor,' leaving open the possibility that the alloy-precursor route fails even if the phase is stable under improved conditions; no controls with known analogs or direct phase identification are described to close this gap.

    Authors: We agree that the abstract wording merits refinement to ensure the experimental conclusion is not overstated. The manuscript already qualifies the result by noting that simultaneous La/Sc deposition may be a key factor, which acknowledges the limitations of the alloy route. In revision we will rephrase the abstract to state that the (La,Sc₂) alloy precursor route did not produce detectable LaSc₂H₂₄ or superconductivity, while explicitly preserving the caveat about alternative synthesis conditions. We will also add a brief clarification that direct phase identification was not performed in these runs. This addresses the concern on the basis of the existing data without altering the reported observations. revision: partial

  2. Referee: [Stability analysis] Stability analysis (ξ = 0.54): the quantitative definition of the stability parameter ξ, the pressure range over which it is evaluated, and the explicit numerical comparison to the corresponding value for LaH₁₀ at 140-150 GPa are not provided in sufficient detail to confirm that the compound sits at a comparable stability edge; this underpins the central claim linking marginal stability to synthesis difficulty.

    Authors: We accept that additional explicit detail on the stability parameter would strengthen the presentation. In the revised manuscript we will supply the quantitative definition of ξ, confirm that the value ξ = 0.54 is evaluated at 250–300 GPa, and include the corresponding numerical value obtained for fcc-LaH₁₀ at 140–150 GPa to enable direct comparison. These additions will make the analogy to marginal stability fully transparent while leaving the underlying analysis unchanged. revision: yes

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper derives Tc > 300 K at 300 GPa via the tetrahedral electron-phonon method (contrasted explicitly with sigma-broadening dependence) and obtains ξ = 0.54 from direct stability analysis of the metallic state at 250-300 GPa. These steps are presented as independent computations. The unsuccessful synthesis from (La,Sc2) alloy is reported as a separate experimental observation, not used to derive the theoretical stability or Tc values. No quoted equations or steps reduce by construction to inputs, fitted parameters renamed as predictions, or load-bearing self-citations. The derivation chain remains self-contained.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The paper relies on standard DFT and electron-phonon methods from prior literature. The main free parameter is the arbitrary sigma broadening. No new entities are postulated. The stability metric ξ appears derived from existing frameworks.

free parameters (1)
  • σ
    Arbitrary broadening parameter in electron-phonon calculations whose value strongly affects predicted Tc(σ).
axioms (2)
  • domain assumption The tetrahedral integration method for electron-phonon coupling is free of arbitrary parameters and accurate for this system.
    Invoked to prefer it over sigma-broadening and support Tc > 300 K claim.
  • standard math Standard assumptions of density functional perturbation theory apply to high-pressure La-Sc hydrides.
    Underlying both computational approaches described.

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discussion (0)

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Reference graph

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