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Researchers look for magnetic-field screening in hydrogen-rich superconductors by measuring how a sample’s magnetization changes as an applied magnetic field is swept. A 6 October 2026 addendum to a 2022 study of H3S and LaH10 clarifies how the team estimates the field at which the initial, approximately linear Meissner response begins to change—and why that estimate is difficult when the sample is tiny, the pressure cell has its own magnetic signal, and the magnetometer becomes noisier at higher fields. The authors interpret their measured hysteresis loops as evidence of superconductivity; a published critique disputes whether the magnetic measurements establish that conclusion.
What the 2026 addendum changes
The addendum revisits the analysis of magnetic-screening measurements reported by Minkov and coauthors in 2022. It focuses on how a field-penetration threshold is read from magnetization-versus-field data, rather than presenting the threshold as a directly observed boundary free of interpretation.
In the approach described by the authors, researchers identify the initial, approximately linear part of the virgin magnetization curve—the response associated with the Meissner region—and estimate the penetration field from where the measured curve departs from that trend. The departure is an inferred point, so its location can depend on the fitting range and on how the background and sample geometry are treated. The addendum discusses measurement noise and demagnetizing correction as factors affecting the parameter estimates.
This distinction matters: the measurement is a magnetization curve, while the penetration threshold and quantities derived from it are estimates interpreted from that curve. The addendum argues that the hysteresis loops support the superconducting state, but the extraction of a threshold remains sensitive to experimental and analytical conditions. Minkov and coauthors’ 2026 addendum
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Why the measurement is difficult at megabar pressure
The experiments place a minute sample inside a miniature diamond anvil cell, which compresses the material to extreme pressure. The cell is not magnetically invisible: its own response contributes a background to the signal attributed to the sample. Separating those contributions is challenging when the sample volume is very small.
The addendum describes SQUID magnetometry measurements on H3S at approximately 155 ± 5 GPa and LaH10 at approximately 130 ± 8 GPa. The applied field was swept from −1 to +1 T, with measurements repeated several times at each temperature. The authors also identify increased noise at higher fields in the SQUID system as a limitation. Together, cell background and field-dependent noise make it harder to determine exactly where a curve departs from its initial linear trend. The addendum’s methods and findings
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The original 2022 paper described a miniature diamond-anvil-cell design capable of reaching pressures as high as 220 GPa; that is a reported capability of the design, not the pressure used in every measurement. The 2022 study
What values the original study reported
The 2022 article reported the following approximate values. They are estimates from that study’s analysis, not universal constants or values independently established by the 2026 addendum.
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| Reported quantity | H3S | LaH10 |
|---|---|---|
| Zero-temperature lower critical field | Approximately 0.82 T | Approximately 0.55 T |
| London penetration depth | Approximately 20 nm | Approximately 30 nm |
| Ginzburg–Landau parameter | Approximately 12 | Approximately 20 |
| Upper-critical-field estimate used in the analysis | Approximately 97 T | Approximately 143.5 T |
The addendum’s methodological point is relevant to interpreting these figures: estimates involving the penetration field depend on the chosen fitting range, measurement noise, and demagnetizing correction. The table reproduces the approximate reported parameters, not a claim that the addendum re-established them. Minkov et al., Nature Communications, 2022; Minkov et al., Nature Communications, 2026
What magnetic screening can—and cannot—show
Magnetic susceptibility provides a way to test for superconducting behavior independently of electrical resistance, and magnetic measurements can help infer quantities such as lower critical field and penetration depth. But a magnetic signature in a high-pressure experiment is not necessarily a simple picture of all applied field being expelled. A 2024 review notes that strong vortex pinning can make the Meissner effect subtle or barely observable in H3S and LaH10; magnetic flux may also remain trapped after the external field is removed. These effects complicate interpretation of both field expulsion and hysteresis. The 2024 review in National Science Review
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Accordingly, it is useful to separate three claims: what the instrument records (a magnetic response as field changes), what the analysis estimates (such as a penetration threshold), and what researchers infer about the material’s state. The addendum authors make the last inference strongly, writing that “the hysteresis loops recorded in H3S and LaH10 (Figs. 1, 2) unambiguously confirm the superconducting state in these highly compressed hydrides.” That is their interpretation of the loops, not a consensus statement.
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High-pressure superconductivity research uses more than one way to probe magnetic behavior. A 2024 review discusses SQUID magnetometry, coil-based susceptibility measurements, and nitrogen-vacancy (NV) sensing with diamond anvils. They offer different kinds of information; the review does not establish one as a universal replacement for the others.
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| Approach | What it probes | What to bear in mind for tiny high-pressure samples |
|---|---|---|
| SQUID magnetometry | Magnetization as the applied field changes; hysteresis and departures from an initial response can be analyzed. | The pressure cell contributes a magnetic background, and the 2026 addendum reports greater noise at higher fields in its SQUID measurements. |
| Coil-based susceptibility | Magnetic susceptibility, providing a magnetic-response measurement. | The 2024 review discusses this as a distinct method; detailed comparative sensitivity, pressure range, and temperature range are not stated here. |
| NV sensing with diamond anvils | Local magnetic response sensed using nitrogen-vacancy centers in diamond. | It can provide local rather than solely bulk-style information; the reviewed material does not state a single pressure or temperature range applicable to all implementations. |
These categories describe different measurement strategies, not interchangeable verdicts. For any particular experiment, the important questions are what magnetic quantity is measured, how the apparatus background is separated from the sample response, and how the signal is interpreted. The 2024 review’s discussion of measurement methods
Why the interpretation remains disputed
The 2026 addendum authors say their H3S and LaH10 hysteresis loops confirm superconductivity. In contrast, J. E. Hirsch and F. Marsiglio’s 2023 critique argues that published magnetic measurements do not establish superconductivity in hydrides under pressure. This is a disagreement about what the available magnetic evidence demonstrates, not a resolution supplied by the addendum alone. Hirsch and Marsiglio’s 2023 critique
For readers assessing the claim, the central methodological issue is therefore not simply whether a curve has a loop or a change in slope. It is how convincingly the measured sample response can be distinguished from cell background and noise, how the field-penetration point is selected, and whether the resulting magnetic behavior supports the physical interpretation. The addendum clarifies the authors’ method and its limitations; it does not make the published disagreement disappear.
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