Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session A1: Competing Order in High-Tc Superconductors |
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Sponsoring Units: DCMP Chair: Erica Carlson, Purdue University Room: Colorado Convention Center Four Seasons 2-3 |
Monday, March 5, 2007 8:00AM - 8:36AM |
A1.00001: Quantum melting of the hole crystal in the spin ladder of Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ Invited Speaker: The ``spin ladder'' is a reduced-dimensional analogue of the t-J model that has been shown theortically to exhibit close competition between d-wave superconductivity and a ``hole crystal" (HC) phase in which the carriers form a static lattice. An example of a real doped spin ladder is the cuprate Sr$_{14-x}$Ca$_{x}$Cu$_{24}$O$_{41}$, which exhibits superconductivity at $x=13.6$ (under pressure) and a commensurate HC at $x=0$. In this talk I will present a resonant soft x-ray scattering (RSXS) study of the effects of discommensuration on this HC, i.e. how it evolves with the hole density. As $x$ is varied the HC forms only with the commensurate wave vectors $L=1/5$ and $L=1/3$; for incommensurate values it ``melts.'' A simple scaling between $L$ and temperature is observed, $\tau_{1/3} / \tau_{1/5} = 5/3$, indicating an inverse relationship between the interaction strength and the HC period. Our results suggest that the HC consists of hole pairs crystallized through an interplay between lattice commensuration and a poorly screened Coulomb interaction. I will discuss the relationship between the HC and the static ``stripe" phase that has been observed in the closely related system La$_{2-x}$Ba$_x$CuO$_4$. [Preview Abstract] |
Monday, March 5, 2007 8:36AM - 9:12AM |
A1.00002: An intrinsic Cu-O-Cu bond-centered electronic glass with disperse 4$a_0$-wide unidirectional domains in strongly underdoped Ca$_{1.88}$Na$_{0.12}$CuO$_2$Cl$_2$ and Bi$_2$Sr$_2$Dy$_{0.2}$Ca$_{0.8}$Cu$_2$O$_y$ Invited Speaker: Hole doping into the CuO$_2$ charge transfer insulator alters the electronic correlations, leading to the high-$T_{\rm c}$ superconductivity (HTS). The correlation alterations are accompanied by spectral weight transfers from the high energy states of the insulator to low energies. Recently, it has been proposed~[1,2] that these effects might be observable as an asymmetry of electron tunneling currents with bias voltage across the chemical potential. Atomic-scale TA-phenomena would then be of crucial importance to understand the fundamental electronic structure of the CuO$_2$ plane from whence the HTS emerges.\par In this talk, we will report the first application of atomic resolution TA-imaging by STM, detecting virtually identical phenomena in two different lightly hole-doped cuprates: Ca$_{1.88}$Na$_{0.12}$CuO$_2$Cl$_2$ and Bi$_2$Sr$_2$Dy$_{0.2}$Ca$_{0.8}$Cu$_2$O$_y$. We find intense spatial variation primarily on planer oxygen sites. Their spatial arrangements appear to be a Cu-O-Cu bond-centered electronic glass, breaking translational symmetry of lattice and 90$^{\circ}$-rotational symmetry. 4$a_0$-wide unidirectional domains ($a_0$: Cu-O-Cu length) are embedded throughout this matrix and running along the both Cu-O bonds without preferred orientation. Relationship to the electronic cluster glass, the bond-centered stripe, and the high-$T_{\rm c}$ superconductivity will be discussed.\par \par This work is done in collaboration with C. Taylor, A. Schmidt, C. Lupien, T. Hanaguri, M. Azuma, M. Takano, K. Fujita, H. Eisaki, H. Takagi, S. Uchida, and J. C. Davis. \par \par [1] P. W. Anderson, N. P. Ong, cond-mat/0405518 \& {\it J. Phys. Chem. Solid} {\bf 67}, 1 (2006).\par [2] M. Randeria, R. Sensarma, N. Trivedi, F. -C. Zhang, {\it Phys. Rev. Lett.} {\bf 95}, 137001 (2005). [Preview Abstract] |
Monday, March 5, 2007 9:12AM - 9:48AM |
A1.00003: Nature of the electronic gap in stripe-ordered cuprates Invited Speaker: The {\it ab}-plane optical properties of single crystals of the high-temperature superconductor La$_{2-x}$Ba$_x$CuO$_4$, with chemical dopings of $x=0.095$ (slightly underdoped) and $0.125$ ($1/8$ doping) and critical temperatures ($T_c$'s) of 32 and $\simeq 2.4$~K, respectively, have been measured over a wide frequency and temperature range. The optical conductivity has been determined from a Kramers-Kronig analysis. In the slightly underdoped material, the reflectance increases monotonically over the far-infrared frequency range, with an abrupt increase in the reflectance below $T_c$ below about 200~cm$^{-1}$ (about 25~meV) signaling the formation of a superconducting energy gap; the suppression of the conductivity for $T\ll T_c$ occurs below this energy. This is close to the estimate of the gap maximum $2\Delta_0$ determined from angle resolved photoemission spectroscopy. In contrast, the 1/8 doping shows a dramatically different behavior.\footnote{C.C.~Homes {\it et al.}, Phys. Rev. Lett. {\bf 96}, 257002 (2006).} The reflectance increases monotonically with decreasing temperature. Below $\simeq 60$~K, corresponding to the onset of charge-stripe order, the far-infrared reflectance continues to increase; however, the reflectance over much of the infrared is suppressed. The conductivity, Drude-like above the ordering temperature, shows a rapid loss of spectral weight below about 40~meV for $T < 60$~K. This behavior is quite different from that typically associated with the pseudogap in the normal state of the cuprates. Instead, the gapping of the normal-state single-particle excitations looks surprisingly similar to that observed in superconducting La$_{2-x}$Sr$_{x}$CuO$_4$, including the presence of a residual Drude peak with reduced weight. [Preview Abstract] |
Monday, March 5, 2007 9:48AM - 10:24AM |
A1.00004: Neutron scattering evidence for spin and charge inhomogeneity in cuprate superconductors Invited Speaker: Neutron diffraction studies have provided clear evidence for charge and spin stripe order in La$_{2-x}$Ba$_{x}$CuO$_{4}$ and La$_{1.6-x}$Nd$_{0.4}$Sr$_{x}$CuO$_{4}$ for a range of $x$, with a maximum ordering temperature at $x$ = 1/8. The ordering of stripes competes with superconducting order. Recent measurements of the magnetic excitation spectrum in La$_{1.875}$Ba$_{0.125}$CuO$_{4}$ show that: 1) the energy scale corresponds to antiferromagnetic superexchange, 2) the qualitative features do not change when static stripe order disappears [1], and 3) the spectrum is very similar to that found in other cuprate superconductors. New measurements on optimally-doped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ [2] are consistent with the concept of a universal spectrum. Results on over-doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ show that the magnetic spectral weight disappears as the superconductivity goes away [3]. These results suggest that slowly-fluctuating charge inhomogeneity is common to the cuprates and underlies the high-temperature superconductivity. \begin{enumerate} \item Guangyong Xu, J.M. Tranquada, T.G. Perring, G.D. Gu, M. Fujita, and K. Yamada, (unpublished). \item Guangyong Xu, J.M. Tranquada, B. Fauqu\'{e}, G.D. Gu, M. H\"{u}cker, T.G. Perring, L.-P. Regnault, and J.S. Wen, (unpublished). \item S. Wakimoto, K. Yamada, J.M. Tranquada, C.D. Frost, R.J. Birgeneau, and H. Zhang, cond-mat/0609155. \end{enumerate} [Preview Abstract] |
Monday, March 5, 2007 10:24AM - 11:00AM |
A1.00005: Duality and the vibrational modes of a Cooper-pair Wigner crystal Invited Speaker: When quantum fluctuations in the phase of the superconducting order parameter destroy the off-diagonal long range order, duality arguments predict the formation of a Cooper pair Wigner crystal. This effect is thought to be responsible for the static checkerboard patterns observed recently in various underdoped cuprate superconductors by means of scanning tunneling spectroscopy. I will sketch the calculation of the vibrational modes of this pair crystal using a continuum version of the standard vortex-boson duality. Such calculations yield bounds on the sound velocity of the phonon modes which are in agreement with the numbers extracted from the thermal conductivity measurements but indicate that vibrations are robustly three dimensional in nature. Generalization of the inherently two-dimensional vortex-boson duality to three dimensions is outlined and an intriguing connection to the theory of bosonic strings is pointed out. [Preview Abstract] |
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