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Author: Fennie, C.J. ×

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    Strain-stabilized superconductivity
    ([London] : Nature Publishing Group UK, 2021) Ruf, J.P.; Paik, H.; Schreiber, N.J.; Nair, H.P.; Miao, L.; Kawasaki, J.K.; Nelson, J.N.; Faeth, B.D.; Lee, Y.; Goodge, B.H.; Pamuk, B.; Fennie, C.J.; Kourkoutis, L.F.; Schlom, D.G.; Shen, K.M.
    Superconductivity is among the most fascinating and well-studied quantum states of matter. Despite over 100 years of research, a detailed understanding of how features of the normal-state electronic structure determine superconducting properties has remained elusive. For instance, the ability to deterministically enhance the superconducting transition temperature by design, rather than by serendipity, has been a long sought-after goal in condensed matter physics and materials science, but achieving this objective may require new tools, techniques and approaches. Here, we report the transmutation of a normal metal into a superconductor through the application of epitaxial strain. We demonstrate that synthesizing RuO2 thin films on (110)-oriented TiO2 substrates enhances the density of states near the Fermi level, which stabilizes superconductivity under strain, and suggests that a promising strategy to create new transition-metal superconductors is to apply judiciously chosen anisotropic strains that redistribute carriers within the low-energy manifold of d orbitals.
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    Formation of heavy d-electron quasiparticles in Sr3Ru2O7
    (Milton Park : Taylor & Francis, 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.