Calcium Ruthenate Ca2RuO4 Comes of Age

by Tommy on 30/03/2017

I have questions. I want answers.

Observation of localized high-Tc superconductivity in a Ca2RuO4 nanofilm single crystal, Hiroyoshi Nobukane, Kosei Yanagihara, Yuji Kunisada, Yunito Ogasawara, Kazushige Nomura, Yasuhiro Asano and Satoshi Tanda (28 March 2017)

We report two-dimensional superconducting phase fluctuations in a Ca2RuO4 nanofilm single crystal. A thin film of Ca2RuO4 exhibits typical Kosterlitz-Thouless transition behaviour around TKT = 30 K. We also found that the bias current applied to the thin film causes a superconducotor-insulator transition at low temperatures. The film is superconductive for small bias currents and insulating for large bias currents. The two phases are well separated by the critical sheet resistance of the thin film 16.5 kΩ. In addition to these findings, our results suggest the presence of superconducting fluctuations at a high temperature T = 96 K with onset. The fabrication of nanofilms made of layered material enables us to discuss rich superconducting phenomena in ruthenates.

Sr2RuO4 is already super interesting.

And contentious! That’s always fun.

See also: a penetrating neutron spectroscopy study of this system.

Magnon dispersion in Ca2RuO4: impact of spin-orbit coupling and oxygen moments, S. Kunkemöller, E. Komleva, S. V. Streltsov, S. Hoffmann, D. I. Khomskii, P. Steffens, Y. Sidis, K. Schmalzl and M. Braden (29 March 2017)

The magnon dispersion of Ca2RuO4 has been studied by polarized and unpolarized neutron scattering experiments on crystals containing 0, 1 and 10 % of Ti. The entire dispersion of transverse magnons can be well described by a conventional spin-wave model with interaction and anisotropy parameters that agree with density functional theory calculations. Spin-orbit coupling strongly influences the magnetic excitations, which is most visible in large energies of the magnetic zone-center modes arising from magnetic anisotropy. We find evidence for a low-lying additional mode that exhibits strongest scattering intensity near the antiferromagnetic zone center. This extra signal can be explained by a sizable magnetic moment of 0.11 Bohr magnetons on the apical oxygens parallel to the Ru moment, which is found in the density functional theory calculations. The energy and the signal strength of the additional branch are well described by taking into account this oxygen moment with weak ferromagnetic coupling between Ru and O moments.

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