Investigation of the disruption of magnon gap and Weyl Fermion in SrRuO₃ single crystal films by inelastic neutron scattering

SrRuO3 in powder [1] and single crystal [2] forms were found to exhibit a magnon gap due to the Weyl fermion node nearby its Fermi surface. To understand the defect effect on the magnon gap and Weyl fermion, we follow the fact that the massive Ru defects and some oxygen vacancies can be easily created when SrRuO3 is grown in a thin film format. In this study, two single crystalline ferromagnetic SrRuO3 films were prepared by the PLD method and examined by Inelastic neutron scattering experiments at SIKA, ANSTO. We found that both films show clear magnon dispersion curves following quadratic relation along [002] direction. The film with fewer defects was found to have a dispersion curve with a small magnon gap of around 0.32meV [3], which is much smaller than Itoh’s and Jenni’s observations. We proposed a model, the impurity level near Fermi level, due to Ru and O vacancies, could weaken the spin-orbit coupling and the anticrossings, and eventually destroy the Weyl Fermion node. In addition, the electrons captured by defects and vacancies induce on-site Coulomb interactions that open a small magnon gap. Meanwhile, the magnon gap for the defect-rich film shows a zero magnon gap, strongly indicating the existence of Weyl fermion node is very sensitive to the presence of defects.

1. S. Itoh, Y. Endoh, T. Yokoo S. Ibuka, J. -G. Park, Y. Kaneko, K. S. Takahashi, Y. Tokura, and N. Nagaosa, Nat. Commun. 7, 11788 (2016).

2. K. Jenni, S. Kunkemo¨ller, D. Bru¨ning, T. Lorenz, Y. Sidis, A. Schneidewind, A. A. Nugroho, A. Rosch, D. I. Khomskii, and M. Braden, Phys. Rev. Lett. 123, 017202 (2019).

3. G. D. Dwivedi, C.-M. Wu, Bo-Yu Chen, S. T. Lin, W.-Z. Qiu, S. J. Sun, Guangyong Xu, J. W. Lynn, J. W. Chiou, C.-H Lee, W.-H. Li, S. Yano, and H. Chou, Phys. Rev. B 101, 054403 (2021).