Abstract
By tuning the physical and chemical pressures of layered perovskite materials we can realize the quantum states of both superconductors and insulators. By reducing the thickness of a layered crystal to a nanometer level, a nanofilm crystal can provide novel quantum states that have not previously been found in bulk crystals. Here we report the realization of high-temperature superconductivity in Ca2RuO4 nanofilm single crystals. Ca2RuO4 thin film with the highest transition temperature Tc (midpoint) of 64 K exhibits zero resistance in electric transport measurements. The superconducting critical current exhibited a logarithmic dependence on temperature and was enhanced by an external magnetic field. Magnetic measurements revealed a ferromagnetic transition at 180 K and diamagnetic magnetization due to superconductivity. Our results suggest the co-appearance of superconductivity and ferromagnetism in Ca2RuO4 nanofilm crystals. We also found that the induced bias current and the tuned film thickness caused a superconductor-insulator transition. The fabrication of micro-nanocrystals made of layered material enables us to discuss rich superconducting phenomena in ruthenates.
Highlights
By tuning the physical and chemical pressures of layered perovskite materials we can realize the quantum states of both superconductors and insulators
The superconductivity in Ca2RuO4 thin film crystals is expected to be robust against external magnetic fields, and play an important role when applied to a topological quantum computation[20]
We describe superconducting phenomena at high temperature induced by ferromagnetism in thin films of Ca2RuO4
Summary
By tuning the physical and chemical pressures of layered perovskite materials we can realize the quantum states of both superconductors and insulators. By tuning the film thickness in the monolayer to the nanometer range, transition metal dichalcogenides realize an exotic ground state different from that of bulk crystals due to a negative pressure effect[6,7]. In rutheno-cuprate superconductors[18,19], superconductivity and ferromagnetism appear to coexist in different layers of layered perovskite structures where the superconductivity is confined to the antiferromagnetic CuO2 planes and is not caused by the spin-triplet pairing associated with the ferromagnetism of the. High-Tc ferromagnetic superconductors have yet to be found, while the spin-triplet superconductivity and superfluidity that have been reported were realized at very low temperatures. The superconductivity in Ca2RuO4 thin film crystals is expected to be robust against external magnetic fields, and play an important role when applied to a topological quantum computation[20]
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