Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session H23: Superconductivity: Mainly ARPES |
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Sponsoring Units: DCMP Chair: Myron Salamon, University of Texas at Dallas Room: D165 |
Tuesday, March 22, 2011 8:00AM - 8:12AM |
H23.00001: Doping dependence of the electron-phonon and electron-spin fluctuation interactions in Bi-2212 Elbert Chia, Daniel Springer, Saritha Nair, Xinaquan Zou, Siew Ann Cheong, Christos Panagopoulos, Antoinette Taylor, Tsuyoshi Tamegai, Hiroshi Eisaki, Shigeyuki Ishida, Shin-ichi Uchida, Jian-Xin Zhu In the BCS theory of conventional superconductors, electrons form (Cooper) pairs via interactions with the underlying crystal lattice. In the cuprate superconductors, it is not clear whether Cooper pairing takes place via electrons interacting with phonons, spin fluctuations, or whether a bosonic mechanism is necessary at all. Though time-integrated optical measurements on the cuprates can give information on the coupling strength between electrons and an effective boson, it is difficult to tell whether one or more bosons are involved, or the nature of these bosons. We report measurements of time-resolved quasiparticle relaxation of Bi$_2 $Sr$_2 $CaCu$_2 $O$_{8+\delta } $ single crystals (hole concentration $p$ = 0.10-0.22). Our data indicate that \textit{two} bosonic modes are associated with superconductivity: the electron-phonon coupling constant ($\lambda _{e-ph} )$ peaks at optimal doping, while the electron-spin fluctuation coupling constant ($\lambda _{e-sf} )$ decreases monotonically with doping. [Preview Abstract] |
Tuesday, March 22, 2011 8:12AM - 8:24AM |
H23.00002: Time-Resolved ARPES Study of Non-Equilibrium Quasiparticle Dynamics in Cuprate Superconductors Christopher Smallwood, Jeff Graf, Chris Jozwiak, Hiroshi Eisaki, Robert Kaindl, Dung-Hai Lee, Alessandra Lanzara We use Time- and Angle-Resolved Photoemission (TR-ARPES) to measure the relaxation dynamics of low energy excitations in the cuprate superconductor Bi-2212. We find an as-yet unreported temperature dependence in nodal quasiparticle spectral weight which is sensitive to the critical temperature. We also find possible evidence for non-thermal transient electronic behavior. [Preview Abstract] |
Tuesday, March 22, 2011 8:24AM - 8:36AM |
H23.00003: Ultra High Resolution Pump Probe Angle Resolved Photoemission Experiments on High Temperature Superconductor Bi2Sr2CaCu2O8 Wentao Zhang, Chris Smallwood, Chris Jozwaik, Hiroshi Eisaki, Alessandra Lanzara Ultra high resolution laser-based pump probe angle-resolved photoemission measurements have been carried out on underdoped Bi2Sr2CaCu2O8 high temperature superconductor. In this talk, we will report on the observation and analysis of quasiparticle relaxation in Bi2Sr2CaCu2O8. [Preview Abstract] |
Tuesday, March 22, 2011 8:36AM - 8:48AM |
H23.00004: Bands, spin fluctuations and traces of Fermi surfaces in ARPES intensities on high-$T_C$ cuprates Thomas Jarlborg The band structures of pure and hole doped La$_2$CuO$_4$ with anti-ferro magnetic (AFM) spin-fluctuations are calculated and compared to spectral weights of ARPES. It is shown that the observation of coexisting Fermi surface (FS) arcs and closed FS pockets are consistent with antiferromagnetic spin fluctuations of varying wave lengths. The FS signal of the underlying non-magnetic material is mixed with echos of FS-breaks from domains with AFM spin waves. Large variations of strong spin fluctuations make the outer part of the FS break diffuse at low doping. This part of the FS is suppressed at high doping when spin fluctuations becomes weak. The resulting superimposed spectral weight has features both from FS arcs and closed pockets. This makes a connection between results of ARPES and neutron scattering, and it implies that spin-phonon coupling is an important mechanism for cuprate properties. [Preview Abstract] |
Tuesday, March 22, 2011 8:48AM - 9:00AM |
H23.00005: Origin of magnetic resonance spectrum in cuprate high-temperature superconductors and related issues A. Bansil, Tanmoy Das, R.S. Markiewicz A distinct low energy magnetic mode has been observed in almost all the cuprate materials in a broad range of experiments including ARPES, Raman, optical, STM, RIXS, as well as neutron scattering. This mode is enhanced in the superconducting (SC) state and its energy scales universally as $\omega_{res} \propto2\Delta$, suggesting that these modes play an important role in the mechanism of superconducting pairing. Here we study this resonance via first-principle susceptibility calculations in a Hubbard model with $d-$wave superconductivity [1]. The resulting excitation mode produces the universal $\omega_{res}\propto 2\Delta$ relation as well as the puzzling `hour-glass' dispersion and the 45$^{\circ}$ rotation of the spin excitations with energy in a series of cuprates in accord with experiments [2]. Work supported by US DOE.\\[4pt] [1] Tanmoy Das, R.S. Markiewicz, and A. Bansil, Phys. Rev. B {\bf 81}, 174504 (2010).\\[0pt] [2] A. Bansil, {\it et al.} Journal of Physics and Chemistry of Solids (2010). [Preview Abstract] |
Tuesday, March 22, 2011 9:00AM - 9:12AM |
H23.00006: Particle-hole asymmetric components of QPI in the pseudogap phase of underdoped Bi-2212 C.K. Kim, Jhinhwan Lee, K. Fujita, H. Eisaki, S. Uchida, J.C. Davis, Jinho Lee QPI visualized by SI-STM became an extremely useful tool in the study of complex electronic matter. Particle-hole(p-h) symmetric QPI observed in the superconducting cuprates revealed many interesting phenomena including the disappearance of the QPI signal around the reduced zone boundary[1], and the persisting QPI signal above the T$_{c}$[2]. Recently, the most dominating band of Sr$_{3} $Ru$_{2}$O$_{7}$ was identified above the metamagnetic nematic phase transition temperature by analyzing p-h asymmetric QPI [3]. Also p-h asymmetric QPI in the parent compound of the ferropnictide superconductor revealed a nematic like electronic structure[4]. Within the same rationale, it is of great interest to find the QPI signature of the band before the superconducting gap opens in the cuprates. Here we explore QPI with particle-hole asymmetric dispersion in the pseudogap phase of underdoped Bi$_ {2}$Sr$_{2}$CaCu$_{2}$O$_{8}$; it appears to disperse continuously through E$_{F}$. Our measured value of the v$_{F}$ of this dispersion is 0.2$\times$10$^{6} $m/s which compares well with the reported value 1.7eV{\AA} from ARPES. We will discuss the possible origin of this QPI by examining its symmetry and dispersion near the zone boundary using theoretical models and currently available experimental data from other probes. [1] Y. Kohsaka et al., Nature(2008) [2] Jhinhwan Lee et al., Science(2009) [3] Jinho Lee et al., Nature Physics(2009) [4] T.-M. Chuang et al., Science(2010) [Preview Abstract] |
Tuesday, March 22, 2011 9:12AM - 9:24AM |
H23.00007: Oxygen reduction effects on the electronic structures of electron doped cuprates: investigating the mechanism of the metal insulator transition D.J. Song, S.R. Park, C.S. Leem, Chul Kim, Y.K. Kim, S.K. Choi, W.S. Jung, C. Kim, H. Eisaki, D.H. Lu, Z.-X. Shen, S. Ishida, S. Uchida In electron doped cuprates, oxygen reduction process not only induces superconductivity but also causes changes in many physical properties. In order to understand these oxygen reduction effects, we performed ARPES studies on as-grown and de-oxygenated superconducting electron doped cuprates, PLCCO, NCCO and SCCO. We observe Fermi surface topology change and pseudo gap filling due to weakening of AFM as reported in other studies. In addition, sharp quasi-particles (QP) appear out of broad incoherent features as the as-grown samples are de-oxygenated through the oxygen reduction process. We believe that this behavior of the QP peak closely related to the insulator to metal transition in the reduction process. We attribute the suppression of the QP states in as-grown sample to the Anderson localized electron states due to strong disorder and impurity scattering. [Preview Abstract] |
Tuesday, March 22, 2011 9:24AM - 9:36AM |
H23.00008: Renormalization of f-levels away from the Fermi energy in electron excitation spectroscopies: Density functional results of Nd$_{2-x}$Ce$_x$CuO$_4$ B. Barbiellini, T. Jarlborg, H. Lin, R.S. Markiewicz, A. Bansil Relaxation energies for photemission, when an occupied electronic state is excited, and for inverse photoemission, when an empty state is filled, are calculated within the density functional theory with application to Nd$_{2-x}$Ce$_x$CuO$_4$ (NCCO). The associated relaxation energies are obtained by computing differences in total energies between the ground state and an excited state in which one hole or electron is added into the system. The relaxation energies of f-electrons are found to be of the order of several eV's, indicating that f-bands will appear substantially away from the Fermi energy ($E_F$) in their spectroscopic images, even if these bands lie close to the $E_F$ in the ground state of NCCO. Our analysis explains why it would be difficult to observe f electrons at the $E_F$ even in the absence of strong electronic correlations. Work supported by the US DOE. [Preview Abstract] |
Tuesday, March 22, 2011 9:36AM - 9:48AM |
H23.00009: Differential heat capacity studies of Nd$_{2-x}$Ce$_{x}$CuO$_{4}$ John Cooper, James Storey, Edward Cavanna, John Loram The electronic heat capacity of several \textit{hole}-doped cuprate systems has been determined accurately over a wide temperature range using a unique differential calorimeter. It gives important thermodynamic information about the electronic excitations and the pseudogap [1] that is difficult to obtain in other ways, so it is clearly of interest to extend these studies to some \textit{electron}-doped materials. Here we report progress in measuring the specific heat capacity of a series of polycrystalline Nd$_{2-x}$Ce$_{x}$CuO$_{4}$ samples with x varying from 0.14 to 0.18 in steps of 0.01, between 2K and 100K, in magnetic fields from 0 -- 13T and complementary magnetic and transport data. The aims of this work are to look for possible signatures of the pseudogap and to compare our results with recent quantum oscillation studies [2]. \\[4pt] [1] For example, J. W. Loram \textit{et al}., J. Phys. Chem. Solids \textbf{62}, 59 (2001). \\[0pt] [2] T. Helm \textit{et al}., Phys. Rev. Lett. \textbf{103}, 157002 (2009). [Preview Abstract] |
Tuesday, March 22, 2011 9:48AM - 10:00AM |
H23.00010: Consequences of two-dimensionality for the quantum oscillations in underdoped YBCO Neil Harrison, Suchitra Sebastian, Moaz Altarawneh, RX. Liang, D.A. Bonn, W.N. Hardy, Gil Lonzarich We report new high resolution measurements on underdoped YBCO over an unprecedented magnetic field range with a high signal- to-noise ratio. The reduced-dimensionality of the Fermi surface is found to strongly influence the quantum oscillations and result in unusual properties. Careful analysis of these unconventional properties is found to severely constrain the Fermi surface topology. [Preview Abstract] |
Tuesday, March 22, 2011 10:00AM - 10:12AM |
H23.00011: Lifshitz transitions in the underdoped cuprates with spin-density wave order Jie Lin It has recently been proposed that a neck-disrupting Lifshitz transition can explain the disappearance of quantum oscillations and diverging cyclotron mass observed in underdoped YBCO. We found that both pocket-disappearing and neck-disrupting types of Lifshitz transitions can be realized in two-dimensional spin-density wave models for underdoped cuprates. Close to Lifshitz transitions, the impurity relaxation rate acquires strong energy-dependence. The thermoelectric power is strongly enhanced, and behaves differently for the two types of transitions. [Preview Abstract] |
Tuesday, March 22, 2011 10:12AM - 10:24AM |
H23.00012: ABSTRACT WITHDRAWN |
Tuesday, March 22, 2011 10:24AM - 10:36AM |
H23.00013: Observation of Electronic Structures on Alkali-earth Metal Intercalated Superconducting GICs Wonshik Kyung, C.S. Leem, Chul Kim, Y.K. Kim, G.R. Han, C. Kim, J.S. Kim, Y.W. Kim We synthesized alkali-metal intercalated GICs(Ca, Ba, Sr). To compare electronic structure of these GICs, we performed high resolution angle-resolved photoemission spectroscopy (ARPES) on it. Through quantitative analysis of band structure, we can see alkali metal dependent band structure. [Preview Abstract] |
Tuesday, March 22, 2011 10:36AM - 10:48AM |
H23.00014: Evidence of nodes in the non-centrosymmetric superconductor Y$_{2}$C$_{3}$ J. Chen, H.Q. Yuan, M.B. Salamon, S. Akutagawa, J. Akimitsu In a non-centrosymmetric superconductor, antisymmetric spin-orbit coupling (ASOC) can admix spin-singlet and spin-triplet pairing states, leading to accidental nodes in the energy gap [1]. Y$_{2}$C$_{3}$ is such a superconductor with a T$_{c}$ of 18K. Early NMR and $\mu $SR results [2] indicated a gap structure incompatible with either BCS s-wave or typical d-wave behavior. To further elucidate its superconducting properties, we have measured the temperature dependence of the magnetic penetration depth using a tunneling-diode oscillator technique. While the high temperature penetration depth, and therefore its corresponding superfluid density, can be well described by a two-gap BCS model, as discussed in Ref. [2], the low temperature penetration depth follows a linear temperature dependence, indicating possible existence of nodes in the energy gap. Together with the large upper critical field observed in Y$_{2}$C$_{3}$ [3], the existence of nodes, we argue, might be attributed to the ASOC as a result of absent inversion symmetry even though other possibilities cannot be excluded. [1] H. Q. Yuan et al, Phys. Rev. Lett. \textbf{97}, 017006 (2006). [2] A. Harada et al, J. Phys. Soc. Jpn. \textbf{76}, 023704(2007); S. Kuroiwa et al, Phys. Rev. Lett. \textbf{100}, 097002 (2008). [3] H. Q. Yuan et al, J. Phys. Chem. Solids (in press). [Preview Abstract] |
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