Last year was awash with claims that researchers had found new high-temperature superconductors. While some of those claims were quickly quashed, others are still being explored, such as the report that single crystals of the nickelate La₃Ni₂O₇ can superconduct at up to 78 K when under a pressure of 18 gigapascals (GPa) [1]. Now experiments performed by Jinguang Cheng of the Chinese Academy of Science and colleagues strengthen the claim that this compound is indeed a superconductor [2]. If confirmed, these results would make La₃Ni₂O₇ one of the few transition-metal compounds outside of cuprates to superconduct at temperatures above the boiling point of liquid nitrogen.

The initial report of superconductivity in La₃Ni₂O₇ came from measurements of single crystals. Those experiments showed a sudden drop in electrical resistance at around 80 K in samples held at pressures above 14 GPa. However, the report lacked measurements of two key hallmarks of a material entering the superconducting state—its resistance falling to zero and the expulsion of external magnetic fields.

For their experiments, Cheng and his colleagues studied polycrystalline samples of La₃Ni₂O₇ subjected to pressures of up to 18 GPa. The researchers chose polycrystalline samples over single-crystal ones, as they are significantly easier to prepare. Their resistance measurements indicated the zero-resistance state needed to confirm the presence of superconductivity. But the researchers’ attempts to detect the magnetic hallmark of superconductivity failed. Cheng says that recent unpublished results from their lab show that doping La₃Ni₂O₇ with the lanthanide praseodymium increases the superconducting temperature to 82.5 K. In those experiments, he says, the team observed both superconducting hallmarks.

Muon spectroscopy serves as a crucial experimental method for exploring the magnetic characteristics of materials. This technique involves embedding a spin-polarized muon within the crystal lattice and observing the impact of the surrounding environment on its behavior. It operates on the principle that the muon will settle into a specific location predominantly influenced by electrostatic forces, a position that can be pinpointed through the calculation of the material’s electronic structure.

But a new study led by scientists in Italy, Switzerland, UK, and Germany has found that, at least for some materials, that is not the end of the story: the muon site can change due to a well-known but previously neglected effect, magnetostriction.

Pietro Bonfà from the University of Parma, lead author of the study just published in Physical Review Letters, explains that his group and their colleagues at the University of Oxford (UK) have been using density-functional theory (DFT) simulations for at least a decade to find muon sites.

Inspired by amphibians such as the wood frog, investigators designed and synthesized a new type of camouflage skin involving one-dimensional photonic crystal structures assembled in three-dimensional flexible gels.

As described in Advanced Optical Materials, the camouflage skin can quickly recognize and match the background by modulating the optical signals of external stimuli.

It demonstrated excellent mechanical performance, self-adaptive camouflage capabilities in response to complex surroundings, and long-term stability in real-world living environments. Bright structural color and mechanical flexibility were maintained even at temperatures as low as-80℃