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Publisher: College Park, Md. : APS × Subject: Calculations ×

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    Normal State O 17 NMR Studies of Sr2RuO4 under Uniaxial Stress
    (College Park, Md. : APS, 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.
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    Coexistence of Superconductivity and Charge Density Waves in Tantalum Disulfide : Experiment and Theory
    (College Park, Md. : APS, 2020) Kvashnin, Y.; VanGennep, D.; Mito, M.; Medvedev, S.A.; Thiyagarajan, R.; Karis, O.; Vasiliev, A.N.; Eriksson, O.; Abdel-Hafiez, M.
    The coexistence of charge density wave (CDW) and superconductivity in tantalum disulfide (2H-TaS2) at low temperature is boosted by applying hydrostatic pressures to study both vibrational and magnetic transport properties. Around Pc, we observe a superconducting dome with a maximum superconducting transition temperature Tc=9.1 K. First-principles calculations of the electronic structure predict that, under ambient conditions, the undistorted structure is characterized by a phonon instability at finite momentum close to the experimental CDW wave vector. Upon compression, this instability is found to disappear, indicating the suppression of CDW order. The calculations reveal an electronic topological transition (ETT), which occurs before the suppression of the phonon instability, suggesting that the ETT alone is not directly causing the structural change in the system. The temperature dependence of the first vortex penetration field has been experimentally obtained by two independent methods. While a d wave and single-gap BCS prediction cannot describe the lower critical field Hc1 data, the temperature dependence of the Hc1 can be well described by a single-gap anisotropic s-wave order parameter. © 2020 authors. Published by the American Physical Society.