Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session D2: New Developments in HTSC II |
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Sponsoring Units: DCMP Chair: Erica Carlson, Purdue University Room: Morial Convention Center LaLouisiane C |
Monday, March 10, 2008 2:30PM - 3:06PM |
D2.00001: Anomalous Electron-Phonon Coupling in Cuprates and its Doping Dependence Invited Speaker: Dmitry Reznik It is well known that conventional superconductivity is mediated by phonons. Phonon renormalization at specific wavevectors (Kohn anomalies) appears in phonon dispersions in many of these compounds with high T$_{c}$s in agreement with LDA calculations. In the case of the cuprates, LDA calculations predict neither any significant Kohn anomalies nor electron-phonon coupling strong enough to account for high T$_{c}$ superconductivity. However, inelastic neutron and x-ray scattering experiments found huge softening and broadening of the bond-stretching phonons indicating that electron-phonon coupling in the cuprates is much stronger than expected from LDA. In the LaSrCuO family phonon renormalization has been observed in the vicinity of the reduced in-plane wavevector q$_{in}$=(0.25, 0) (in units of (2$\pi $/a,2$\pi $/a where a is the near-neighbor Cu-Cu distance). The effect is strongest at low temperatures and in compositions that exhibit the so-called stripe order where it occurs at the wavevector that corresponds to the charge order. Detailed \textbf{q}-dependent studies revealed that the underlying electronic instability is 2D in nature in the 214 compounds, i.e. for q$_{in}$=(0.25, K), it is peaked at K=0 with the full width at half maximum of about 0.15 r.l.u. The strength of this phonon renormalization tracks T$_{c}$ disappearing at the nonsuperconducting extremes of doping. In YBCO the similar phonon anomaly is quasi-1D with bond-stretching phonon renormalization occurring around q$_{in}$=(H, 0.25) for all investigated H (in units of (2$\pi $/a,2$\pi $/b where a/b is the near-neighbor Cu-Cu distance in the direction paralle/perpendicular to the Cu-O chains). Relationship between these effects and band structure will be explored. Experimental results will also be compared with expectations of LDA-based calculations as well as with predictions of models based on dynamic stripes. [Preview Abstract] |
Monday, March 10, 2008 3:06PM - 3:42PM |
D2.00002: Doping Dependent Anisotropic Electronic Scattering rate in LSCO Invited Speaker: Joel Mesot An angle-resolved photoemission study of the scattering rate in the normal and superconducting states of the high-temperature superconductor La(2-x)Sr(x)CuO(4) as a function of binding energy and momentum will be presented. We report that, close to optimal doping, the scattering rate scales linearly with binding energy up to a high-energy scale E1. The scattering rate is found to be strongly anisotropic, with a minimum along the nodal direction of the superconducting gap. SInce both the degree of anisotropy and the energy dependence of the scattering rate appear to be strongly doping dependent, possible connections to a quantum-critical point will be discussed. [Preview Abstract] |
Monday, March 10, 2008 3:42PM - 4:18PM |
D2.00003: Fermi surface of underdoped cuprate revealed by quantum oscillations and Hall effect Invited Speaker: Cyril Proust Despite twenty years of research, the phase diagram of high temperature superconductors remains enigmatic. A central issue is the origin of the differences in the physical properties of these copper oxides doped to opposite sides of the superconducting region. In the overdoped regime, the material behaves as a reasonably conventional metal, with a large Fermi surface [1]. The underdoped regime, however, is highly anomalous and appears to have no coherent Fermi surface, but only disconnected `Fermi arcs' [2]. We have reported the observation of quantum oscillations in the electrical resistance of the oxygen-ordered copper oxides YBa$_{2}$Cu$_{3}$O$_{6.5}$ [3] and YBa$_{2}$Cu$_{4}$O$_{8}$ [4], establishing the existence of a coherent closed Fermi surface at low temperature in the underdoped side of the phase diagram of cuprates, once superconductivity is suppressed by a large magnetic field. The low oscillation frequency reveals a Fermi surface made of small pockets, in contrast to the large cylinder characteristic of the overdoped regime. Moreover, the negative sign of the Hall effect at low temperature reveals that these pockets are electron-like rather than hole-like. We propose that the Fermi surface of these Y-based cuprates consists of both electron and hole pockets, probably arising from a reconstruction of the FS [5]. Work in collaboration with N Doiron-Leyraud, D. LeBoeuf and L. Taillefer from the University of Sherbrooke, J. Levallois and B. Vignolle from the LNCMP, A. Bangura and N. Hussey from the University of Bristol and R. Liang, D. Bonn, W. Hardy from the University of British Columbia. \newline [1] N Hussey et al, \textit{Nature} \textbf{425}, 814 (2003) \newline [2] M. Norman et al, \textit{Nature} \textbf{392}, 157 (1998) \newline [3] N. Doiron-Leyraud et al, \textit{Nature} \textbf{447}, 565 (2007) \newline [4] A. Bangura et al, submitted to \textit{Phys. Rev. Lett} (arXiv: 0707.4461) \newline [5] D. LeBoeuf et al, \textit{Nature} \textbf{450}, 533 (2007) [Preview Abstract] |
Monday, March 10, 2008 4:18PM - 4:54PM |
D2.00004: Fermi orbits versus Fermi arcs Invited Speaker: Neil Harrison We consider the effect of a short antiferromagnetic correlation length $\xi$ on the electronic bandstructure of the underdoped cuprates. Starting with a Fermi-surface topology thought to be consistent with that detected in magnetic-quantum-oscillation experiments, we show that a reduced $\xi$ gives an asymmetric broadening of the quasiparticle dispersion, resulting in simulated ARPES data very similar to those observed in experiment. Predicted features include the presence of `Fermi arcs' close to $a{\bf k}=(\pi/2,\pi/2)$, where $a$ is the in-plane lattice parameter, without the need to invoke a $d$-wave pseudogap order parameter. The statistical variation in the $k$-space areas of the reconstructed Fermi-surface pockets causes the quantum oscillations to be strongly damped, even in very strong magnetic fields, in agreement with experiment. (I would like to extend special thanks to the coauthors John Singleton and Ross McDonald and to E. Yelland and L. Taillefer for useful discussions). [Preview Abstract] |
Monday, March 10, 2008 4:54PM - 5:30PM |
D2.00005: Fermi surface and anisotropic scattering in overdoped cuprates Invited Speaker: Nigel Hussey In the light of recent results detailing the emergence of small Fermi pockets and anomalous Hall coefficients in underdoped cuprates, we review here our measurements on the Fermiology and low temperature transport of cuprates that reside on the other side of the superconducting dome. Analysis of angle-dependent magnetoresistance and Hall coefficient data in Tl$_{2}$Ba$_{2}$CuO$_{6+\delta }$ and La$_{2-x}$Sr$_{x}$CuO$_{4}$ has uncovered a wealth of structure, not only in the (un-reconstructed) Fermi surface in overdoped cuprates, but also in the basal-plane transport scattering rate, in both the elastic and the inelastic channels. A striking correlation between the superconducting transition temperature and the strength of the anisotropic scattering is also revealed suggesting an intimate link between anisotropic scattering and the pairing mechanism itself. Finally, we discuss possible origins of these various anisotropic terms and how they might impact on our understanding of the evolution of the resistivity and the Hall coefficient across the entire cuprate phase diagram. [Preview Abstract] |
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