Nature Materials volume 21, pages 1102–1103 (2022)Cite this article
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Resonant X-ray scattering experiments have revealed a charge-ordered phase next to the recently discovered superconducting phase in layered nickelates — in remarkable analogy to the cuprate high-temperature superconductors.
Researchers in the field of high-temperature superconductivity have long appreciated how lucky they are. The effective Coulomb repulsion between conduction electrons, which is responsible for this phenomenon, has to have just the right strength. If it is too weak, the materials behave like ordinary metals without a superconducting ground state. If it is too strong, the electrons localize at the atomic sites and the material becomes insulating. In the phase diagram of the cuprates (Fig. 1a), the high-temperature superconducting phase is therefore nestled at the border between a magnetically ordered ‘Mott insulator’ with localized electrons and a ‘Fermi liquid’ phase with properties akin to those of conventional metals1. Recent research has shown that the situation is even more delicate as charge-ordered states with partially localized electrons encroach on the superconducting phase, leading to a depression of the superconducting transition temperature Tc. The application of high magnetic fields or uniaxial pressure enhances the charge order and further degrades or even obliterates superconductivity2,3. It is hard to escape the notion that under slightly different circumstances, high-Tc superconductivity would not have been stable under ambient conditions.
