Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 29: Superconductivity: Mechanisms, Phase Diagram, Competing Order

TT 29.9: Talk

Thursday, February 28, 2008, 12:00–12:15, H 3010

Dynamical magnetic susceptibility in the lamellar cobaltate superconductor Na_xCoO₂· yH₂O — •Maxim Korshunov^1,2 and Ilya Eremin^1,3 — ¹Max-Planck-Institut für Physik komplexer Systeme, Dresden, Germany — ²L.V. Kirensky Institute of Physics, Siberian Branch of RAS, Krasnoyarsk, Russia — ³Institute für Math. und Theor. Physik, TU Braunschweig, Braunschweig, Germany

We systematically analyze the influence of the superconducting gap symmetry and the electronic structure on the dynamical spin susceptibility in superconducting Na_xCoO₂· yH₂O within a three different models: the single a_1g-band model with nearest-neighbor hoppings, the realistic three-band t_2g-model with, and without e′_g pockets present at the Fermi surface. We show that the magnetic response in the normal state is dominated by the incommensurate antiferromagnetic spin density wave fluctuations at large momenta in agreement with experimental temperature dependence of the spin-lattice relaxation rate. Also, we demonstrate that the presence or the absence of the e′_g-pockets at the Fermi surface does not affect significantly this conclusion. In the superconducting state our results for d_x²−y²- or d_xy-wave symmetries of the superconducting order parameter are consistent with experimental data and exclude nodeless d_x²−y² + id_xy-wave symmetry. We further point out that the spin-resonance peak proposed earlier is improbable for the realistic band structure of Na_xCoO₂· yH₂O. Moreover, even if present the resonance peak is confined to the antiferromagnetic wave vector and disappears away from it.

M.K. acknowledges support form INTAS YS Grant 05-109-4891 and RFBR Grant 06-02-90537-BNTS.