Advancements in the High Pressure Growth of Doped Rare-Earth Nickelate Single Crystal

Floating zone grown nickelates

Researchers at the Max Planck Institute for Solid State Research have achieved crucial advancements in the single-crystal synthesis of perovskite rare-earth nickelates, a quantum material known for its exceptional electronic and magnetic properties. Their efforts offer promising avenues for exploring new doping strategies this material class.

Perovskite-structured rare-earth nickelates are at the forefront of material research due to their diverse properties, encompassing phenomena like metal-insulator transitions, unconventional magnetic order, and potential multiferroicity. The richness of these materials arises from the intricate balance and interactions among charge, spin, orbital, and lattice degrees of freedom, positioning them as ideal candidates for both fundamental studies and practical applications.

However, preparing high-quality single crystals of these nickelates is technically demanding. Moreover, our current understanding of how chemical doping alters their properties remains limited. An intriguing discovery has further propelled interest in this domain: the emergence of superconductivity in hole-doped nickelates with the infinite-layer structure after the de-intercalation of oxygen ions from the precursor perovskite structure. Notably, superconductivity has yet only been observed in nickelate thin films, prompting questions about the replicability in the single-crystalline counterparts. Yet, the confirmation of such an occurrence would herald a deeper exploration into the superconducting characteristics of these materials.

In a recent study published in APL Materials, a team from the Max Planck Institute for Solid State Research in Stuttgart (MPI-FKF) has made significant strides in this direction. They have successfully synthesized various perovskite nickelate single crystals using a high-temperature high-pressure optical floating zone technique.

In collaborative effort, the team members from the Institute's Crystal Growth and Interface Analysis Scientific Facilities along with the Department for Solid State Spectroscopy, investigated the effects of hole- and electron-doping in the nickelate crystals. Notably, charge carrier doping due to the substitution of the rare-earth ion by elements like cerium or strontium enhanced the metallic character of the nickelate compounds, while zirconium appeared to weaken the magnetic correlations. Despite encountering challenges, such as the appearance of undesired impurity phases for high substitution levels, the study underscores the efficacy of the utilized method for the crystal growth of complex quantum materials.

Furthermore, the results reveal the pressing need for new, cutting-edge strategies that go beyond the conventional single dopant route to realize high substitution concentrations. For instance, co-doping with multiple ionic species could potentially approximate the high doping levels achieved in thin films, paving the way for superconductivity in topotactically reduced nickelate crystals.