Abstracts of LT23

Session 26aB Session 26aB

Superconducting Order Parameter of Sr₂RuO₄: an Experimental Overview

Yoshiteru Maeno^a, Kazuhiko Deguchi^b, Naoki Kikugawa^c, Hiroshi Yaguchi^b, Kenji Ishida^b

^aInternational Innovation Center and Department of Physics, Kyoto University, Kyoto 606-8501, Japan

^bDepartment of Physics, Kyoto University, Kyoto 606-8502, Japan

^cVenture Business Laboratory and Department of Physics, Kyoto University, Kyoto 606-8501, Japan

We will give an experimental overview of the current understanding of the symmetry of order parameter of the unconventional superconductor Sr₂RuO₄. We will emphasize the importance of understanding the phenomenon of superconducting double transitions, which is closely linked with an unusual suppresion of the upper critical field for the field accurately parallel to the quasi-two-dimensional planes. We also touch upon the implications of the NMR results in the superconducting symmetry and mechanism.

26aB2 paper-pdf

Determination of the directions of gap nodes in exotic superconductors

Yuji Matsuda, Koichi Izawa

Institute for Solid State physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa 277-8581, Japan

The unconventional superconductivity is characterized by the superconducting gap structure with nodes along certain directions. Although the superconducting gap function is crucial for understanding the pairing mechanism, the detailed structure, especially the direction of the nodes, is an unresolved issue in most of unconventional superconductors. Recently it has been demonstrated that the thermal conductivity k is a powerful tool for probing the nodal structure. Here we measured k of spin-triplet Sr₂RuO₄ , quasi-2D heavy fermion CeCoIn₅, organic k-(BEDT)₂Cu(NCS)₂, and borocarbide YNi₂B₂C in magnetic field rotating within the basal planes. We show that the gap functions of Sr₂RuO₄, CeCoIn₅ and k-(BEDT)₂Cu(NCS)₂ are most likely to be d(k) = D₀[^(z)](k_x+ik_y)(cosck_z+a), d_x²-y², and d_xy, respectively. We also demonstrate the presence of point nodes along the a- and b-axes in YNi₂B₂C.

26aB3

Magnetic excitations in 214-ruthenates

M. Braden^a, Y. Sidis^b, O. Friedt^a,^b, P. Bourges^b, P Pfeuty^b, S. Nakatsuji^c, Z. Mao^c, Y. Maeno^c

^aII. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany

^b Laboratoire Léon Brillouin, C.E.A./C.N.R.S., F-91191-Gif-sur-Yvette CEDEX, France

^c Department of Physics, Kyoto University, Kyoto 606-8502, Japan

We discuss magnetic excitations in several 214-ruthenates as observed by inelastic neutron scattering. In the spin-triplet superconductor Sr₂RuO₄ the magnetic excitation spectrum is dominated by incommensurate peaks arising from Fermi surface nesting. Evidence that Sr₂RuO₄ is close to the corresponding spin-density wave ordering is found in the temperature dependence of the spectrum which shows some scaling behavior. The corresponding spin-density wave ordering is finally induced by substituting a small amount of Ru through Ti. The possible role of ferromagnetic fluctuations is further analyzed on the base on Ca-substituted samples which exhibit a strongly enhanced magnetic susceptibility.

26aB4 paper-pdf

Tunneling and phase-sensitive studies of the pairing symmetry in Sr₂RuO₄

Y. Liu^a, Z.Q. Mao^a, K.D. Nelson^a, D. Okuno^a, J.R. Kirtley^b, C.C. Tsuei^b, Y. Maeno^c

^aThe Pennsylvania State University, University Park PA, USA

^bIBM, Yorktown Heights NY, USA

^cKyoto University, Kyoto, Japan

We report the results of our tunneling and phase-sensitive experiments on superconducting, single crystalline Sr₂RuO₄. The tunneling measurements revealed a zero-bias conductance peak (ZBCP) in the tunneling spectra originating from Andreev surface bound states, as well as behavior associated with the time-reversal symmetry breaking in Sr₂RuO₄. These results provide strong support for a spin-triplet, p-wave superconducting pairing state in Sr₂RuO₄. We will also report the status of the phase sensitive experiments.

26aB5 paper-pdf

Competing Orders and Field Induction of D+iD' State

A.V. Balatsky^a, J.X. Zhu^b

^aTheory Division, T-11, MS B 262, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

^bTheory Division, T-11, MS B 262, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

The role of the magnetic field on the d-wave density wave as a model of pseudogap state of cuprates and on the d-wave superconducting state will be addresses. We argue that in d-wave density state magnetic field can produce secondary gap components. This distortion by magnetic field offers a possibility to distinguish between different scenarios of pseudogap in normal state of high-Tc materials. Similarly we argue that magnetic field can distort the p-wave state and produce secondary component of the gap in p-wave superconductor.