Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session P1: Is There Pairing Glue in Cuprate Superconductors? |
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Sponsoring Units: DCMP Chair: C.C. Tsuei, IBM T.J. Watson Research Center Room: Morial Convention Center LaLouisiane AB |
Wednesday, March 12, 2008 8:00AM - 8:36AM |
P1.00001: The Question of Pairing Glue in the Cuprate Superconductors Invited Speaker: The Hubbard and t-J models exhibit many of the properties which are observed in the cuprate superconductors. Thus they provide a framework for addressing the question of whether one should expect to find a ``pairing glue'' in the cuprtates. This question is basically a question regarding the dynamics of the pairing interaction. If the dynamics of the pairing interaction arises from virtual states, whose energies correspond to the Mott gap, and give rise to the exchange coupling J, the interaction is instantaneous on the relative time scales of interest. In this case one would not speak of a pairing glue. However, if the energies correspond to the spectrum seen in the dynamic spin susceptibility, then the interaction is retarded and one could speak of a spin-fluctuation glue which mediates the d-wave pairing interaction. We will review results from recent numerical calculations which provide insight into this question. [Preview Abstract] |
Wednesday, March 12, 2008 8:36AM - 9:12AM |
P1.00002: Strongly Correlated d-wave Superconductivity: a CDMFT Perspective Invited Speaker: We examine the impact of the proximity to a Mott insulating state on the superconduting properties of model system, (t-J and Hubbard) using cluster DMFT on a 2x2 plaquette. We study various observables such as the frequency and doping dependence of the order parameter, the one electron spectra, the optical conductivities, and the spin response. We compare the picture that emerges from these studies with the results of previous approaches such as the slave boson method, and with those of weak coupling approaches where the picture of superconductivity due to exchange of spin fluctuations is more established. [Preview Abstract] |
Wednesday, March 12, 2008 9:12AM - 9:48AM |
P1.00003: The Fluctuating Bond Model, a Glue for Cuprate Superconductivity? Invited Speaker: Twenty years of research have yet to produce a consensus on the origin of high temperature superconductivity (HTS). The mechanism of HTS - which originates in the CuO$_{2}$ plane, common to all HTS families - can be constrained by some key experimental facts regarding superconducting and pseudogap behaviors. Superconductivity, involving a $T_{c}$ of order $100 $K, exhibits an unusual $d$-wave superconducting gap, with Fermi liquid nodal excitations, and an anomalous doping- dependent oxygen isotope shift. A ``pseudogap,'' also with $d$-symmetry, leads to a dip in the density of states below a characteristic temperature scale $T^{\ast }$, which has a \textit{negative} isotope shift; we associate the pseudogap with the recently observed spatially inhomogeneous (nanometer- scale) C$_{4}$ symmetry breaking. The isotope shifts and other evidence imply a key role for oxygen vibrations, but conventional BCS single-phonon coupling is essentially forbidden by symmetry and by the on-site Coulomb interaction $U$. In a novel approach, we introduce a model based on a strong, local, nonlinear interaction between electrons within the Cu-O-Cu bond in the CuO$_{2}$ plane, and the oxygen vibrational degrees of freedom, termed the Fluctuating Bond Model (FBM) [D.M. Newns and C.C. Tsuei, Nature Physics \textbf {3}, 184 (2007)]. In mean field the model predicts a phase manifesting broken C$_{4}$ symmetry, with a $d$-type pseudogap, and an upper phase boundary in temperature, with a negative isotope shift, which we identify with $T^{\ast }$. An intrinsic $d$-wave pairing tendency is found, leading to a transition temperature dome and an anomalous isotope shift similar to that found experimentally. The softening in the oxygen vibrational frequency below $T_{c}$, seen in Raman and neutron spectra, has a natural explanation in the FBM. Recent \textit{ab initio} calculations have been implemented which provide microscopic support for the model. [Preview Abstract] |
Wednesday, March 12, 2008 9:48AM - 10:24AM |
P1.00004: The Normal State Pseudogap in Underdoped Cuprates: Precursor Pairing vs. Competing Order? Invited Speaker: The ``pseudogap'' in the normal state of underdoped High $T_c$ cuprates refers to a set phenomena associated with the loss of low energy spectral weight in various spectroscopies, starting at a temperature $T^\ast(x)$, much higher than $T_c(x)$ and with a completely different doping dependence. Understanding the unusual phenomena in the pseudogap regime, which lies in between the Mott insulator and the optimally doped superconductor, is an important challenge for any theory of high $T_c$ superconductivity. I will first review some of the main experimental facts about the pseudogap, focusing in particular on recent angle-resolved photoemission (ARPES) data. I will then critically examine which aspects of the data can be qualitatively understood in terms of theories of precursor pairing or those based on a competing order parameter. [Preview Abstract] |
Wednesday, March 12, 2008 10:24AM - 11:00AM |
P1.00005: Two-Dimensional Hubbard Model and High-Tc Superconductivity Invited Speaker: |
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