Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S1: Pairing and Symmetry |
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Sponsoring Units: DCMP Chair: John Kirtley, IBM Room: LACC 152 |
Wednesday, March 23, 2005 2:30PM - 3:06PM |
S1.00001: Robust d-wave pairing symmetry in hole-doped cuprate superconductors$\dagger$ Invited Speaker: After a debate over many years, it is widely agreed that an order parameter with $d_{x^2-y^2}$ symmetry has been established in optimally doped cuprate superconductors\footnote{C.C. Tsuei and J.R. Kirtley, Rev. Mod Phys. {\bf 72}, 969 (2000)}. The controversy has now shifted to the possibility of changes in pairing symmetry as a result of doping. In this talk, we will first report new results of a precise measurement on the location of nodes in the d-wave gap function at the Fermi surface of a high-T$_c$ superconductor YBa$_2$Cu$_3$O$_7$. We will then present a series of phase-sensitive tricrystal experiments to demonstrate, using the half-flux quantum effect, that the d-wave pair state in several cuprate systems is robust against a wide range of doping variations from under-doped, through optimal doping, to over-doped regimes. Implications of the findings of this work for understanding high-temperature superconductivity will be discussed at the end of the talk. \\ $\dagger$ work done with J.R. Kirtley, A. Ariando, Hans Hilgenkemp, G. Hammerl, J.Mannhart, H. Raffy, and Z.Z. Li. [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:42PM |
S1.00002: Phase-sensitive test of odd-parity superconductivity in Sr$_{2}$RuO$_{4}$ Invited Speaker: Ying Liu The possibility of odd-parity, spin-triplet pairing of electrons was first pointed out in 1960 after the publication of the BCS theory for superconductivity. Sr$_{2}$RuO$_{4}$, the only Cu-free layered perovskite superconductor, was predicted to be a material featuring such an unusual pairing state. We have in the past several years pursued the phase-sensitive test of odd-parity pairing in Sr$_{2}$RuO$_{4}$ following the proposal of Geshkenbein, Larkin, and Barone (GLB). The experiment involves the preparation and the measurement of GLB SQUIDs consisting two oppositely faced Josephson junctions between an s-wave superconductor, Au$_{0.5}$In$_{0.5}$, and Sr$_{2}$RuO$_{4}$ as well as control samples. We found that the critical current of GLB SQUIDs was a maximum while for control samples of SQUIDs with two junctions prepared on the same side, the critical current is a minimum at zero magnetic flux. This indicates that the phase of the order parameter changes by \textit{$\pi $} under inversion, showing that Sr$_{2}$RuO$_{4}$ is indeed an odd-parity superconductor [1]. More recent results on corner and the same-side junctions of Au$_{0.5}$In$_{0.5}$-Sr$_{2}$RuO$_{4}$ will be presented. [1] K.D. Nelson, Z.Q. Mao, Y. Maeno, and Y. Liu, Science 306, 1151-1154 (2004). [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 4:18PM |
S1.00003: Low temperature scanning SQUID microscopy studies of Sr$_{2}$RuO$_{4}$ Invited Speaker: We present direct imaging of magnetic flux structures in the anisotropic, spin-triplet superconductor Sr$_{2}$RuO$_{4}$ using a scanning SQUID microscope. We detected magnetic flux above the crystallographic ab plane in the superconducting state, at temperatures between 0.35 K and 1.35 Kelvin. Magnetic fields as high as 70 G were applied inplane. Individual quantized vortices were resolved at low perpendicular magnetic fields. At intermediate fields direct imaging revealed coalescing vortices forming flux domains. Based on our observations, we suggest that a pinning mechanism intrinsic to the material stabilizes the flux domains against the repulsive vortex-vortex interaction. Topological defects like domain walls may provide the pinning, implying proof for unconventional chiral superconductivity. We will discuss our observations in view of the predicted vortex domain state in time reversal symmetry breaking superconductors. [Preview Abstract] |
Wednesday, March 23, 2005 4:18PM - 4:54PM |
S1.00004: The State of Superconductivity in the 1D Organics Invited Speaker: We report on the status of the superconducting state in the quasi-1D molecular organic superconductors (TMTSF)$_{2}$X, on this 25$^{th}$ anniversary of organic superconductivity. A number of experimental results over the last decade, mostly on X=ClO$_{4}$ and PF$_{6}$, address the nature of the Cooper pairing in these materials, which surprisingly is not a settled issue. Critical field (via transport), NMR (including Knight shift) and impurity studies are suggestive of unconventional pairing, converging on spin triplet as a top candidate. Muon spin rotation and thermal conductivity results are less conclusive. More recently, the large $H_{c2}$ (well beyond the Pauli limit) has been confirmed by magnetization, and tunneling on a bicrystal shows a large midgap (zero-bias) state, strengthening the case for triplet superconductivity. The talk will include a discussion of the spin triplet configurations ($p$-- and $f$ --wave) available for (TMTSF)$_{2}$X, and will propose an order parameter \textbf{d}-vector consistent with the experiments. \newline \newline Work done in collaboration with Heon-Ick Ha (present address, Harvard University) and Jeong-Il Oh [Preview Abstract] |
Wednesday, March 23, 2005 4:54PM - 5:30PM |
S1.00005: Evolution of superconducting order in Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ Invited Speaker: The filled skutterudite PrOs$_4$Sb$_{12}$ is paradoxical, exhibiting heavy-fermion behavior and unconventional superconductivity absent an ion with a magnetic ground state. Related compounds, PrRu$_4$Sb$_{12}$, LaOs$_4$Sb$_{12}$, and LaRu$_4$Sb$_{12}$ (the last two reported at this conference) are conventional BCS superconductors. To explore the change from unconventional $^3$He like order to fully-gapped conventional order we have measured, with high precision, the penetration depth of the series Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ to low temperatures. We find a persistence of the T$^2$ temperature dependence, found for $x=0$, below a temperature we label $T_{c3} (x)$. The cross over temperature $T_{c3}(x)$ decreases linearly from 0.6 K at $x=0$, appearing to vanish near $x=0.26$. The data above $T_{c3}(x)$, and over the entire range for $x \ge 0.3 $, are well represented by weak-coupling ($0.1\leq x \leq 0.6$) or intermediate-coupling ($x \geq 0.8$) BCS expressions. The results are discussed in terms of proposed mechanisms for unconventional behavior based on the proximity of a triplet excited state to the ground state singlet of the Pr ion.\\ \\Work performed with Elbert E. M. Chia, D. Vandervelde, K. Kikuchi, H. Sugawara and H. Sato and supported by the Department of Energy through the Illinois Materials Research Laboratory [Preview Abstract] |
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