Normal State ^{17}O NMR Studies of Sr_{2}RuO_{4} under Uniaxial Stress

• Main Authors: Yongkang Luo, A. Pustogow, P. Guzman, A. P. Dioguardi, S. M. Thomas, F. Ronning, N. Kikugawa, D. A. Sokolov, F. Jerzembeck, A. P. Mackenzie, C. W. Hicks, E. D. Bauer, I. I. Mazin, S. E. Brown
• Format: Article
• Language: English
• Published: American Physical Society 2019-05-01
• Series: Physical Review X
• Online Access: http://doi.org/10.1103/PhysRevX.9.021044

The effects of uniaxial compressive stress on the normal state ^{17}O nuclear-magnetic-resonance properties of the unconventional superconductor Sr_{2}RuO_{4} are reported. The paramagnetic shifts of both planar and apical oxygen sites show pronounced anomalies near the nominal a-axis strain ϵ_{aa}≡ϵ_{v} that maximizes the superconducting transition temperature T_{c}. The spin susceptibility weakly increases on lowering the temperature below T≃10  K, consistent with an enhanced density of states associated with passing the Fermi energy through a van Hove singularity. Although such a Lifshitz transition occurs in the γ band formed by the Ru d_{xy} states hybridized with in-plane O p_{π} orbitals, the large Hund’s coupling renormalizes the uniform spin susceptibility, which, in turn, affects the hyperfine fields of all nuclei. We estimate this “Stoner” renormalization S by combining the data with first-principles calculations and conclude that this is an important part of the strain effect, with implications for superconductivity.