2019, Luo, Yongkang, Pustogow, A., Guzman, P., Dioguardi, A.P., Thomas, S.M., Ronning, F., Kikugawa, N., Sokolov, D.A., Jerzembeck, F., Mackenzie, A.P., Hicka, C.W., Bauer, E.D., Mazin, I.I., Brown, S.E.

The effects of uniaxial compressive stress on the normal state O17 nuclear-magnetic-resonance properties of the unconventional superconductor Sr2RuO4 are reported. The paramagnetic shifts of both planar and apical oxygen sites show pronounced anomalies near the nominal a-axis strain μaaμv that maximizes the superconducting transition temperature Tc. 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 dxy states hybridized with in-plane O pπ 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. © 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

2013, Allan, M.P., Tamai, A., Rozbicki, E., Fischer, M.H., Voss, J., King, P.D.C., Meevasana, W., Thirupathaiah, S., Rienks, E., Fink, J., Tennant, D.A ., Perry, R.S., Mercure, J.F., Wang, M.A., Lee, Jinho, Fennie, C.J., Kim, E.A., Lawler, M.J., Shen, K.M., Mackenzie, A.P., Shen, Z.X., Baumberger, F.

The phase diagram of Sr3Ru2O7 shows hallmarks of strong electron correlations despite the modest Coulomb interaction in the Ru 4d shell. We use angle-resolved photoelectron spectroscopy measurements to provide microscopic insight into the formation of the strongly renormalized heavy d-electron liquid that controls the physics of Sr3Ru2O7. Our data reveal itinerant Ru 4d-states confined over large parts of the Brillouin zone to an energy range of <6 meV, nearly three orders of magnitude lower than the bare band width. We show that this energy scale agrees quantitatively with a characteristic thermodynamic energy scale associated with quantum criticality and illustrate how it arises from a combination of back-folding due to a structural distortion and the hybridization of light and strongly renormalized, heavy quasiparticle bands. The resulting heavy Fermi liquid has a marked k-dependence of the renormalization which we relate to orbital mixing along individual Fermi surface sheets.