Uncovering origins of heterogeneous superconductivity in La₃Ni₂O₇

Nature News · Feb 25, 2026 · Collected from RSS

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MainNickelate materials play an important part in the decades-long quest to probe, understand and enhance high-temperature (high-Tc) superconductivity24,25,26,27,28,29. They provide a fresh perspective on the unconventional physics of the cuprates1,2,3,4,5,6, realizing similar electronic and structural motifs in a wholly different material platform. For example, the seminal observation of superconductivity in thin-film, square planar nickelates, which are isovalent to the cuprates, hints at a more universal relationship between superconductivity and orbital filling4,25,26,30.More recently, a tremendous amount of excitement has focused on the discovery of superconductivity in the bulk nickelate, La3Ni2O7, with a critical temperature above the boiling point of liquid nitrogen7. This discovery challenges the nascent model connecting nickelate and cuprate physics: La3Ni2O7 exhibits an electronic configuration that is distinct from the cuprates and superconducts only at high pressures ≳10 GPa (refs. 8,9,10,11,12,13,14). These distinctions suggest the potential to both broaden and deepen our understanding of high-Tc superconductivity. However, realizing this potential comes with its own set of obstacles.Perhaps the most important, from a practical perspective, is the presence of substantial variations in the superconducting properties measured across different La3Ni2O7 samples7,9,14,15,16,17. Even when superconductivity is observed, variations exist in the magnitude and sharpness of the drop in resistance, the transition temperature, the local diamagnetic response22,23, the onset pressure and the characteristics of the normal state7,14,16. Moreover, measurements of La3Ni2O7 have also observed very low superconducting volume fractions, leading the superconductivity to be dubbed ‘filamentary’10,15; these observations complicate our understanding of both the nature of nickelate superconductivity and the underlying connection to the cuprates.Marked progress has been made towards a qualitative understanding of the microscopic origins of the above variations, with invocations to local inhomogeneity in the chemistry14,31,32,33, structure15,34 and stress environment9,10,16. However, many questions remain—for example, whether one of the purported forms of inhomogeneity dominates the superconducting response of La3Ni2O7. More quantitatively, it remains unclear whether there is an interplay between these inhomogeneities and whether we can identify the associated parameter space hosting superconductivity. The fact that these questions are fundamentally related to the role of local inhomogeneities makes them extremely difficult to answer. Ideally, we would want to spatially correlate the local superconducting properties of La3Ni2O7 with maps of the various types of inhomogeneity. The difficulty of this pursuit is markedly exacerbated by the high-pressure setting, in which the local imaging of functional material properties remains a perennial challenge.Here, we take a crucial step towards addressing this challenge. With sub-μm spatial resolution, we directly correlate local regions of superconductivity in La3Ni2O7 with spatial maps of both the stress environment and the chemical composition (Fig. 1). This is achieved through our multimodal, wide-field sensing techniques (Fig. 1a), which extend beyond recent confocal studies of high-pressure nickelates22,23. Our main results are threefold. First, by using diamond anvil cells (DACs) instrumented with a shallow layer of nitrogen-vacancy (NV) colour centres18,19,20,21, we perform wide-field, high-pressure, optically detected magnetic resonance spectroscopy (ODMR) to image the local diamagnetic response—associated with the superconducting Meissner effect—in three separate La3Ni2O7 samples: S1 (Fig. 2), S2 (Fig. 3) and S3 (Fig. 5). We note that these samples are carefully chosen to exhibit differing degrees of chemical homogeneity as measured using energy-dispersive X-ray spectroscopy (EDX). Crucially, apart from NV-based measurements of the diamagnetism, we simultaneously measure the transport behaviour of the samples, observing a drop in resistance concomitant with the onset of the Meissner effect (Fig. 2c,d). The proximity of our NV centres to the La3Ni2O7 sample yields excellent magnetic-field sensitivity, which enables the first observation of flux trapping in the nickelates. Moreover, we find a direct correlation between those regions of the sample exhibiting diamagnetism and those that trap flux (Fig. 2e).Fig. 1: Micrometre-scale structure–function mapping at high pressure in an NV-DAC.a, The NV-DAC enables sub-μm-scale imaging of functional magnetic responses of samples at high pressure. Correlating these maps with the local stress environment and chemical composition yields a wealth of structure–function information. b, Schematic of the sample loading. The top anvil contains a layer of NV centres about 500 nm below the culet surface. We note that there is an approximately 3° misalignment between the culet normal and the [111] NV symmetry axis, which is discussed in the Methods. c, White-light image of sample S1 with false colour overlays obtained at 21 GPa. A crystal of La3Ni2O7 (grey) is embedded in NaCl as a pressure medium (tan) within an insulating cBN gasket (dark). d, Schematic of the spin S = 1 sub-levels of the electronic ground state of the NV centre as a function of an external magnetic field HZ. e, The ODMR spectra obtained at regularly spaced pixels along the line-cut indicated after ZFC to 20 K and turning on a magnetic field of H = 97 G. Away from the sample boundaries (points A and B), the measured splitting Δν ≈ 0.27 GHz is consistent with a local B = 97 G, whereas above the sample, there are regions in which Δν is both smaller (magnetic suppression) and larger (enhancement) than normal state expectations. Spectra are scaled to have uniform peak contrast but are otherwise unprocessed. We observe inverted positive contrast peaks, which extend our ability to measure both magnetic fields and traction to higher pressures (see the Methods for details).Full size imageFig. 2: Imaging local superconductivity and flux trapping.a, Sub-μm diffraction-limited maps of sample S1, showing the magnetic field B obtained after ZFC to 20 K, turning on H ≈ 100 G and then field warming (FW). The magnetic ratio s ≡ B/H above the sample deviates from 1 below a dome in the \(\overline{{\sigma }_{ZZ}},T\) plane, although clear spatial inhomogeneities exist. In particular, the asymmetric magnetic textures are suggestive of the Wohlleben effect (Methods). b, Corresponding σZZ maps for these stress points, taken at 150 K. c,d, Simultaneously measured resistance at \(\overline{{\sigma }_{ZZ}}=21\,\mathrm{GPa}\) and 25 GPa, with the ZFC-FW magnetic response of two spatial points marked on a (pink and purple stars, bottom right). Kinks in the magnetic response correspond to kinks in resistance at corresponding stress points. e, Spatial regions of strongest ZFC diamagnetic response (left) at \(\overline{{\sigma }_{ZZ}}=23\,\mathrm{GPa}\) correspond to regions with the most remnant magnetic flux (right) trapped after field cooling (FC) at H = 150 G and quenching to H = 0 G. For the left panel, grey regions correspond to 0.97 ≤ B/H < 1, whereas black regions correspond to 0.85 ≤ B/H < 0.97. For the right panel, green regions correspond to ODMR spectra with NV resonances that were unable to be resolved.Full size imageFig. 3: Local superconductivity and normal stress maps.a,b, Maps of the ZFC-FW magnetic response (a) and normal stress maps of sample S2 (b) analogous to those in Fig. 2 for sample S1. c, Correlation of the resistive transition (above) with the magnetic response (below) at one stress point. Sample S2 shows qualitatively similar diamagnetic and resistive responses to those of sample S1 in the \(\overline{{\sigma }_{ZZ}}-T\) plane but in a smaller spatial volume and with a weaker local s response.Full size imageSecond, using a complementary modality of the NV sensors, we image the three components of the local stress tensor (\(\overleftrightarrow{{\boldsymbol{\sigma }}}\)) that define the so-called traction vector35: \({\bf{f}}=\{{\sigma }_{XZ},{\sigma }_{YZ},{\sigma }_{ZZ}\}\). Crucially, f is continuous across the diamond–sample interface, providing a map of the local stresses experienced by the La3Ni2O7 sample. The traction vector consists of two physically distinct contributions: (1) the normal stress σZZ and (2) the shear stress vector \({\boldsymbol{\tau }}=\{{\sigma }_{XZ},{\sigma }_{YZ}\}\) with magnitude \(\tau =|{\boldsymbol{\tau }}|=\sqrt{{\sigma }_{{XZ}}^{2}+{\sigma }_{{YZ}}^{2}}\), which arises owing to contact friction between the sample and the diamond. Near the critical pressure, we observe the first signatures of superconductivity confined to localized regions of the sample only where the normal stress, σZZ, is sufficiently large (Fig. 4b,c). On further compression, these superconducting regions spread to encompass substantial fractions of the entire sample (Fig. 2a). Perhaps most intriguingly, our spatial maps of the shear stress magnitude, τ, yield the following conclusion: above a critical shear of approximately 2 GPa, the superconducting behaviour of La3Ni2O7 quenches (Fig. 4d,e). Although conventional phase diagrams of nickelate superconductivity depict pressure as a single axis with discrete steps5,7,9,14,16, our ability to measure the local stress environment allows us to access a more refined and continuous ‘pressure’ axis (Fig. 4g,h). By decomposing this pressure axis into its normal and shear components, we arrive at a complex three-dimensional (3D) superconducting phase diagram for La3Ni2O7 as a function of {T, σZZ, τ} (Fig. 4f).Fig. 4: Multimodal correlations, superconducting phase diagram and the role of shear stresses.a, The local surface stoichiometry of sample S1 obtained by EDX shows regular Ni rich inclusions (purple) at the several μm scale as wel