Abstract
High-quality single crystals are essentially needed for the investigation of the novel bulk properties of unconventional superconductors. The availability of such crystals grown by the floating-zone method has helped to unveil the unconventional superconductivity of the layered perovskite Sr2RuO4, which is considered as a strong candidate of a topological spin-triplet superconductor. Yet, recent progress of investigations urges further efforts to obtain ultimately high-quality crystalline samples. In this paper, we focus on the method of preparation of feed rods for the floating-zone melting and report on the improvements of the crystal growth. We present details of the improved methods used to obtain crystals with superconducting transition temperatures Tc that are consistently as high as 1.4 K, as well as the properties of these crystals.
Highlights
The availability of high-quality single crystals is essential for the full clarification of the novel bulk properties of quantum materials, especially of unconventional superconductors
As another characteristic of unconventional superconductivity, the quasiparticle density of states readily emerges within the superconducting gap even with a small amount of impurities and defects [11]; the resulting large residual density of states often makes the determination of the intrinsic gap anisotropy a challenging issue [12,13,14,15]
We focus on the process of feed-rod preparation in order to further improve the quality of Sr2RuO4 crystals
Summary
The availability of high-quality single crystals is essential for the full clarification of the novel bulk properties of quantum materials, especially of unconventional superconductors. Its superconductivity is completely suppressed when the mean-free-path becomes comparable to the superconducting coherence length (≈ 70 nm), corresponding to the impurity level of c.a. 1500 ppm, where the impurities act as strong scattering centers As another characteristic of unconventional superconductivity, the quasiparticle density of states readily emerges within the superconducting gap even with a small amount of impurities and defects [11]; the resulting large residual density of states often makes the determination of the intrinsic gap anisotropy a challenging issue [12,13,14,15]. Despite the key experimental results supporting spin-triplet pairing [19,20,21,22,23], such a first-order transition is difficult to explain within the context of spin-triplet superconductivity This first-order transition becomes second order when the Tc is suppressed below 1.45 K, which corresponds to an impurity level of ~50 ppm [10]. The improved feed-rod preparation processes have allowed for the efficient production of high-quality crystals which will help deepen our understanding of the superconducting state of Sr2RuO4
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