Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session J2: Dynamical Layer Decoupling and Stripe Order High Tc Superconductors |
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Sponsoring Units: DCMP Chair: Eduardo Fradkin, University of Illinois at Urbana-Champaign Room: Spirit of Pittsburgh Ballroom BC |
Tuesday, March 17, 2009 11:15AM - 11:51AM |
J2.00001: Towards two-dimensional superconductivity in La$_{2-x}$Sr$_{x}$CuO$_{4}$ in a moderate magnetic field Invited Speaker: We report a novel aspect of the competition and coexistence between antiferromagnetism and superconductivity in the prototypical high-Tc cuprate La$_{2-x}$Sr$_{x}$CuO$_{4}$ (La214). With a modest magnetic field applied $H \parallel c$-axis, we monitored the infrared signature of pair tunneling between the CuO$_{2}$ planes and discovered the complete suppression of interlayer coupling in a series of La214 single crystals. We find that the in-plane superconducting properties remain largely intact, in spite of increased antiferromagnetism in the planes. Thus, our experiments show that an isolated CuO$_{2}$ plane is capable of maintaining high-Tc superconductivity. The theoretical framework for antiferromagnetic-driven interlayer decoupling is identified in the work of Berg, \emph{et. al.} [E. Berg, \emph{et. al.}, Phys. Rev. Lett. \textbf{99}, 127003 (2007) and Cond-mat arXiv:0810.1564]. [Preview Abstract] |
Tuesday, March 17, 2009 11:51AM - 12:27PM |
J2.00002: Theory of a striped superconductor Invited Speaker: In the spin and charge striped-ordered cuprate La$_{1.875}$Ba$_ {0.125}$CuO$_4$, the bulk superconducting T$_c$ is strongly suppressed to about 4K. Nevertheless, recent experiments revealed unusual superconducting fluctuations far above T$_c$. In particular, these experiments show evidence for 2D superconductivity in this 3D (albeit anisotropic) system, which is unpreceded. We propose an explanation of these results in terms of a new phase, the ``striped superconductor", in which the superconducting order parameter is modulated periodically in space and averages to zero. Such a state can naturally explain the apparent vanishing of the inter-layer Josephson coupling in La$_{1.875}$Ba$_{0.125}$CuO$_4$. We discuss several phenomenological features of this phase, including a unique sensitivity to disorder which can lead to an xy ``gauge glass" phase that breaks time reversal symmetry spontaneously. Possible microscopic mechanisms leading to striped superconductivity will be briefly discussed. [Preview Abstract] |
Tuesday, March 17, 2009 12:27PM - 1:03PM |
J2.00003: Electronic liquid-crystal phases, symmetry breaking and Fermi-surface reconstruction in YBa$_2$Cu$_3$O$_{6+x}$ Invited Speaker: The physics of underdoped cuprates is governed by strong correlations and phase competition, and its understanding remains one of the challenges of condensed-matter research. Here we will discuss our systematic doping- and temperature-dependent neutron-scattering investigation of the spin correlations in underdoped YBa$_2$Cu$_3$O$_{6+x}$ (YBCO) in the context of various proposed symmetry-breaking phases. In YBCO6.45 ($T_c=35$~K), we observe the spontaneous onset of a one-dimensional, incommensurate (IC) modulation of the low-energy ($<10$~meV) spin excitations below $T\sim150$~K, Hinkov \emph{et al., Science} \textbf{319}, 597 (2008). We interpret our finding as the occurrence of an electronic liquid-crystal phase breaking $C4$-symmetry, as predicted by Kivelson \emph{et al., Nature} \textbf{393}, 550 (1998). Below $T\sim30$~K, we observe the onset of quasi-static spin-correlations with the same IC geometry as the low-energy spin excitations. Their intensity is doubled by the application of a magnetic field of 15~T. First of all, this resolves a long-standing discrepancy with the La$_{2-x}$(Sr,Ba)$_x$CuO$_4$ family where field-dependent, IC quasi-static spin correlations were reported before (Lake \emph{et al., Nature} \textbf{415}, 299 (2002)). More importantly, our results show how the recently reported quantum oscillations in high magnetic fields in YBa$_2$Cu$_3$O$_{6.5}$ (Doiron-Leyraud \emph{et al., Nature} \textbf{447}, 565 (2007)) can be understood in terms of a Fermi-surface reconstruction induced by IC spin modulations. In the lack of experimental evidence for such IC modulations, this mechanism has not been pursued in the past, although it was discussed as a straightforward explanation for Fermi-surface reconstruction. Finally, we will discuss YBCO with a $T_c$ of 10~K. Compared to the previous example, there is an enhancement of the quasi-static spin-correlations. In addition, there is indication for incipient commensurate AF order in reminiscence of the AF parent compound. [Preview Abstract] |
Tuesday, March 17, 2009 1:03PM - 1:39PM |
J2.00004: Stripe order, electron pockets, and Fermi arcs Invited Speaker: The recent observation of an electron pocket by quantum oscillation experiments is naturally explained by the presence of magnetic stripe order near 1/8 hole doping in cuprates [1]. A bigger question is how these observations are related to other phenomena in the phase diagram - the pseudogap phase, quantum critical points, and Fermi arcs [2], and the implications this might have for the origin of high temperature superconductivity.\\[4pt] [1] A. J. Millis and M. R. Norman, Antiphase stripe order as the origin of electron pockets observed in 1/8-hole-doped cuprates, Phys. Rev. B 76, 220503 (2007).\\[0pt] [2] M. R. Norman, A. Kanigel, M. Randeria, U. Chatterjee and J. C. Campuzano, Modeling the Fermi arc in underdoped cuprates, Phys. Rev. B 76, 174501 (2007). [Preview Abstract] |
Tuesday, March 17, 2009 1:39PM - 2:15PM |
J2.00005: Magnetic Field and Temperature Dependence of Charge Stripe Order in La2-xBaxCuO4 (x$\sim $1/8). Invited Speaker: We report a comprehensive x-ray scattering study of charge stripe ordering in La2-xBaxCuO4 (x $\sim $ 1/8), for which the bulk superconducting Tc is greatly suppressed. We found that the charge order in this sample is described with one-dimensional charge density waves, which have incommensurate wave-vectors (0.23, 0, 0.5) and (0, 0.23, 0.5) respectively on neighboring CuO2 planes. The structural modulation due to the charge stripe order is simply sinusoidal, and no higher harmonics were observed. Just below the structural transition temperature, short-range charge density wave correlation appears, which then develops into a large scale charge ordering around 40 K, close to the spin density wave ordering temperature. However, this charge ordering fails to grow into a true long range order, and its correlation length saturates at $\sim $23 nm, and slightly decreases below about 15 K. In addition, we report our observation of the unusual magnetic field dependence of the charge order correlation length. Specifically, in the superconducting phase the charge order correlation length increases as the magnetic field greater than $\sim $5 T is applied. [Preview Abstract] |
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