Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session B2: Invited Session: 2D Charge Ordering in Under-Doped Cuprates |
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Sponsoring Units: DCMP Chair: Zhi-Xun Shen, Stanford University Room: Ballroom II |
Monday, March 18, 2013 11:15AM - 11:51AM |
B2.00001: Incommensurate charge density fluctuations in underdoped YBCO detected by resonant x-ray scattering Invited Speaker: Giacomo Ghiringhelli A key issue in high $T_c$ superconductivity is the short and mid range ordering of spin and charge degrees of freedom when doping disrupts the long range antiferromagnetic order of parent compounds. Cu sites are the main, although not the only, actors in the play. Inelastic and elastic scattering of x rays, when performed at the Cu $L_3$ absorption resonance, can be used to map the spin and charge excitation spectra and, simultaneously, to unveil the presence of spatial modulations in the charge or spin densities. We have used angle-resolved resonant inelastic soft x-ray scattering (RIXS) and resonant elastic soft x-ray scattering (REXS) to identify two-dimensional charge fluctuations with an incommensurate periodicity of $\sim3.2$ lattice units in the copper oxide planes of the superconductors (Y,Nd)Ba$_2$Cu$_3$O$_{6+x}$ with hole concentrations $0.09 < p < 0.13$ per planar Cu ion [G. Ghiringhelli et al, Science 337, 821 (2012)]. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature, $T_c$; further cooling below $T_c$ abruptly reverses the divergence of the charge correlations. In combination with prior observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge-density-wave instability that competes with superconductivity. Further measurements on an Ortho III sample have confirmed that the charge fluctuations are independent of the chain ordering [A. J. Achkar et al, Phys. Rev. Lett. 109, 167001 (2012)]. Put into perspective, these results show that often elastic and inelastic x-ray scattering experiments should be ideally performed jointly, to explore with the greatest sensitivity charge and spin fluctuations [L. Braicovich et al, Phys. Rev. Lett. 104, 077002, (2010)]. [Preview Abstract] |
Monday, March 18, 2013 11:51AM - 12:27PM |
B2.00002: Charge and spin correlations in high temperature superconductors Invited Speaker: Stephen Hayden The cuprate high temperatures superconductors are characterised by numerous competing, and in some cases, co-existing broken symmetries. A important question is to what extent such additional ordered states exist for compositions with high superconducting transition temperatures. I will discuss high-energy X-ray diffraction measurements which show that a charge density wave state (CDW) develops at zero field in the normal state of superconducting YBa$_2$Cu$_3$O$_{6.67}$ ($T_c$ = 67 K). This material has a hole doping of 0.12 per copper and a well-ordered oxygen chain superstructure. Below $T_c$, the application of a magnetic field suppresses superconductivity and enhances the CDW. We find that the CDW and superconductivity are competing orders with similar energy scales, and the high-$T_c$ superconductivity forms from a pre-existing CDW environment. Our results provide a mechanism for the formation of small Fermi surface pockets which can explain the negative Hall and Seebeck effects and the $T_c$ plateau in this material. [Preview Abstract] |
Monday, March 18, 2013 12:27PM - 1:03PM |
B2.00003: Interplay between the pseudogap, mode coupling and superconductivity in Bi-based cuprates Invited Speaker: Makoto Hashimoto Complexity of the high-Tc cuprate superconductors is partly due to the coexisting energy scales that are of the order of superconducting gap ($<$50 meV). The pseudogap ($<$100 meV) and bosonic mode ($<$100 meV) could be relevant to superconductivity, but they have not been understood in a unified picture. We first show the commencement of the pseudogap state at temperature T* using three different techniques (ARPES, polar Kerr effect, and Time-resolved reflectivity) on the same optimally doped Bi2201 crystals. The result suggests that the pseudogap is a disinct phase that shows broken symmetry,\footnote{M. Hashimoto* and R.-H. He* et al., Nat. Phys. 6, 414-418, (2010).}$^,$\footnote{R.-H. He* and M. Hashimoto* et al., Science 331, 1579-1583, (2011).} which could be consistent with the two-dimentional charge ordering observed by STM and scattering measurements. Further, we discuss how this distinct pseudogap order is entangled with superconductivity below Tc. In Bi2212, by analyzing the ARPES spectral weihgt in the antinodal region, we show compelling evidence for the dynamic competition between the two order parameters for the pseudogap and superconductivity as a function of temperature.\footnote{M. Hashimoto et al., (2013)} Such competition can naturally result in the shift of the critical point for the pseudogap.\footnote{I. M. Vishik et al., PNAS 109, 18332-18337 (2012)} Moreover, by studying the detailed temperature and doping dependence of the spectral lineshape in the antinodal region, we reveal that the interplay between the pseudogap, bosonic-mode coupling and superconductivity with similar energy scales is crucial and they have to be considered in a integrated picture to understand the cuprates electronic structure.\footnote{He, Hashimoto, Science 331} \\[4pt] *These authors equally contributed to the work. [Preview Abstract] |
Monday, March 18, 2013 1:03PM - 1:39PM |
B2.00004: Pseudogap signatures measured in the Fermi surface of underdoped YBCO by quantum oscillations Invited Speaker: Suchitra E. Sebastian Solving the riddle of the pseudogap state in underdoped high temperature superconductors is critical to the understanding of the origin of high temperature superconductivity. Quantum oscillations performed on single crystals of the family of underdoped YBCO cuprates reveal small Fermi surface pockets in the normal state accessed at low temperatures and high magnetic fields. It has been widely thought, however, that high magnetic fields cause this state to be significantly different from the mysterious pseudogap state measured at high temperatures and low magnetic fields. In this talk I will present a quantum oscillation study of underdoped YBa$_2$Cu$_3$O$_{\rm {6+x}}$ up to magnetic fields of 100 T that reveals a dimensional collapse of the Fermi surface due to a drastic reduction in c-axis hopping, identical to the pseudogap signature measured in the low magnetic field regime. We therefore conclude that the fundamental properties of the pseudogap are encoded in the Fermi surface, an understanding of which is critical to uncovering the origin of the pseudogap in high temperature superconductors. Possible mechanisms are discussed to explain the origin of the Fermi surface in underdoped YBa$_2$Cu$_3$O$_{\rm {6+x}}$. This work was performed in collaboration with G. Lonzarich (University of Cambridge), N. Harrison, M. Altarawneh, F. Balakirev (Los Alamos National Laboratory), and R. Liang, W. Hardy, D. Bonn (University of British Columbia) [Preview Abstract] |
Monday, March 18, 2013 1:39PM - 2:15PM |
B2.00005: Ultrasonic signatures at the superconducting and the pseudogap phase boundaries in cuprates Invited Speaker: Albert Migliori A major issue in the understanding of cuprate superconductors is the nature of the metallic state from which high temperature superconductivity emerges. Central to this issue is the pseudogap region of the doping-temperature phase diagram that extends from room temperature to the superconducting transition. To date there is no thermodynamic evidence for a phase boundary. We address this by measuring the elastic response of detwinned single crystals and observe a discontinuity in the elastic moduli across the superconducting transition with magnitude requiring that pair formation is coincident with superconducting coherence and a phase transition at the pseudogap boundary. In slightly overdoped YBCO that transition is below Tc, extending the pseudogap phase boundary inside the superconducting dome. This supports a description of the metallic state in cuprates where a pseudogap phase boundary evolves into a quantum critical point masked by the superconducting dome. [Preview Abstract] |
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