Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session K37: Superconductivity-Time Resolved Optical and Inelastic x-ray Scattering in Cuprates |
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Sponsoring Units: DCMP Chair: David Tanner, University of Florida Room: Baltimore Convention Center 340 |
Tuesday, March 14, 2006 2:30PM - 2:42PM |
K37.00001: Ultrafast, Time-Resolved Quasiparticle Dynamics in Hg-Based High Temperature Superconductors X. Li, M. Khafizov, R. Sobolewski, S. Chromik, V. Strbik, D. De Barros, P. Odier We present our all optical and optoelectronic time-domain studies of the quasiparticle and Cooper pair dynamics in Hg-based superconductors. The samples were mixed phase (Hg-1212 and Hg-1223), $c$-axis-oriented thin films, fabricated by magnetron sputtering, followed by \textit{ex-situ} mercuration. The films exhibited the onset of the superconducting transition at T$_{c}$ = 123 K and the zero-resistance at 110 K. Far below T$_{c}$, our femtosecond pump-probe spectroscopy studies clearly demonstrated the bi-molecular-type relaxation of photoexcited quasiparticles, governed by the direct Cooper pair formation process. At temperatures close to T$_{c}$, we observed a severe phonon bottleneck, and the quasiparticle relaxation time was limited by the phonon anharmonic decay/escape process. The photoresponse studies performed on current-biased microbridges, illuminated by femtosecond optical pulses demonstrated the picosecond nonequilibrium response on top of the much slower bolometric signal. [Preview Abstract] |
Tuesday, March 14, 2006 2:42PM - 2:54PM |
K37.00002: Time-resolved infrared spectroscopy of superconducting NbTiN films H. Zhang, D.H. Reitze, C.J. Stanton, D.B. Tanner, R.P.S.M. Lobo, G.L. Carr Time-resolved, pump-probe measurements of superconducting thin NbTiN films were performed at the National Synchrotron Light Source, Brookhaven National Laboratory. Near-infrared Ti:sapphire laser pulses break Cooper pairs, producing an excess of non-thermal quasiparticles. The recombinations of these excess quasiparticles are probed by time-synchronized, far-infrared, synchrotron pulses, with a time resolution of order 200 picoseconds. The main process probed is the bottleneck between gap-edge quasiparticles and excess 2$\Delta $ phonons. (The phonons, generated by recombination of quasiparticles into Cooper pairs, are pairbreaking, producing gap-edge quasiparticles.) We will report the temperature, magnetic field, and laser fluence dependence of the spectrum-averaged far-infrared photoinduced transmission and reflection. We will also report the changes in the photoinduced far-infrared transmission spectrum. [Preview Abstract] |
Tuesday, March 14, 2006 2:54PM - 3:06PM |
K37.00003: Finite bandwidth effects in time-domain measurements of fast electronic processes Ofer Naaman, Jos\'{e} Aumentado Using rf reflectometry, we have observed individual quasiparticle tunneling events in a superconducting single- charge transistor. These events follow a Poisson process on microsecond time scales. We show that when the measurement is done with a finite bandwidth receiver, the experimentally observed process is no longer Poissonian, and the measured transition rates always underestimate those in the underlying system. We will present a model that accounts for bandwidth effects in these time-domain measurements, and show how to obtain the underlying rates from their measured values. We compare the results of our model to simulated and experimental data. We argue that these effects, which are significant even if the receiver is 10 times faster than the process, are a general feature in time domain experiments. [Preview Abstract] |
Tuesday, March 14, 2006 3:06PM - 3:18PM |
K37.00004: Determination of electron--phonon interaction parameters from time--domain terahertz spectroscopy J. Steven Dodge, M. A. Gilmore, Saeid Kamal, D. M. Broun We present an analytical framework for determining metallic electron--phonon interaction parameters from time--domain terahertz spectroscopy measurements in the normal state. We apply this analysis to the case of lead, where we obtain values that are consistent with existing estimates. We discuss the statistical and systematic errors that limit the uncertainty in the parameter estimates. [Preview Abstract] |
Tuesday, March 14, 2006 3:18PM - 3:30PM |
K37.00005: Hole doping in YBa$_2$Cu$_3$O$_{6+\delta}$ from polarization dependent x-ray absorption spectroscopy David Hawthorn, Darren Peets, Kyle Shen, Suman Hossain, George Sawatzky, Thomas Kroll, Jonathan Denlinger, Ruixing Liang, Doug Bonn, Walter Hardy We present detailed polarization dependent x-ray absorption spectroscopy (XAS) measurements of the cuprate YBa$_2$Cu$_3$O$_{6+\delta}$ as a function of oxygen concentration for (0 $\leq \delta \leq$ 1). By adding O into the chain layer of YBCO, holes are doped into both the CuO$_2$ planes and CuO$_3$ chains. The presence of O induced states is directly observed by measurements of the O K edge and Cu L edge XAS, which probes unoccupied states in the O $2p$ and Cu $3d$ orbitals respectively. Owing to the different symmetry of the Cu d orbitals in the planes ($d_ {x^2-y^2}$) and chains ($d_{y^2-z^2}$), the contribution to the total XAS from the chains and planes is clearly separated by measuring the polarization dependence of the x-ray absorption. Comparison to LDA calculations of the unoccupied density of states are used to obtain a quantitative measure of the hole doping in the planes and chains as a function of O concentration. In addition, the doping of holes into the CuO$_2$ planes as a function of degree of oxygen order in the chains is observed by measuring YBa$_2$Cu$_3$O$_{6.5}$ in both the chain ordered (ortho II) and chain disordered phases. This provides direct evidence for the role of chain ordering on hole doping in YBCO. [Preview Abstract] |
Tuesday, March 14, 2006 3:30PM - 3:42PM |
K37.00006: Doping Dependence of Resonant Inelastic X-ray Scattering (RIXS) in Electron and Hole-doped Cuprates Arun Bansil, Robert Markiewicz, Yinwan Li, Dong Qian, Zahid Hasan Resonant inelastic X-ray scattering (RIXS) can in principle access all intra- and inter-band transitions over a wide range of energies and momenta. For these reasons, RIXS is emerging as an important probe of Mott gap physics in strongly correlated materials. Here we discuss evolution of RIXS spectra in electron and hole doped cuprates within the framework of a three-band model Hamiltonian[1]. The theoretical predictions are compared and contrasted with the corresponding experimental results in NCCO and LSCO[2]. Interband (magnetic) transitions are found to shift to lower energy with increasing doping, while intraband features appear away from half-filling and spread over a wider energy range as the bandwidth grows with doping. Higher energy features arising from transitions deeper within the cuprate valence band complex will also be discussed. 1: R.S. Markiewicz and A. Bansil, cond-mat/0506474. 2: M.Z. Hasan, {\it et al.}, cond-mat/0406654. [Preview Abstract] |
Tuesday, March 14, 2006 3:42PM - 3:54PM |
K37.00007: Resonant Inelastic X-ray Scattering (RIXS) Studies in the Cuprates Robert Markiewicz, Arun Bansil Resonant inelastic X-ray scattering (RIXS) is emerging as a probe of Mott gap physics in strongly correlated materials. Here we discuss some details of our recent three-band model[1] calculations for the cuprates. We discuss Mott vs Slater physics in the three-band model, aspects of magnetic gap collapse in the cuprates, and calculational details including polarization and initial energy dependence and relation of the band model to cluster calculations. 1: R.S. Markiewicz and A. Bansil, cond-mat/0506474. [Preview Abstract] |
Tuesday, March 14, 2006 3:54PM - 4:06PM |
K37.00008: Electronic Excitations in the Resonant X-Ray Scattering Spectra of La$_{2}$CuO$_{4}$ David Ellis, John Hill, Shuichi Wakimoto, Diego Casa, Thomas Gog, Young-June Kim Resonant inelastic X-Ray scattering (RIXS) experiments were done on the insulating cuprate La$_{2}$CuO$_{4}$ (LCO), tuning the incident energy to the copper k-edge at 8.99 keV to probe excitations on the order of an eV. With an energy resolution of 130 meV, a number of new features in the electronic excitations could be resolved. The momentum dependence of these features was studied in detail. In LCO, distinct peaks were seen above 2 eV, the first of which is associated with the charge-transfer excitation between the copper and the neighboring oxygen atoms. The amplitude of this peak decreased with increasing momentum transfer q, and energy increased with an observed dispersion of at least 0.2 eV. These results were interpreted using a 1-band model calculation. Also seen was a non-dispersive feature at 1.8 eV thought to be an orbital d-d excitation. [Preview Abstract] |
Tuesday, March 14, 2006 4:06PM - 4:18PM |
K37.00009: Quantum melting of the hole crystal in the spin ladder of Sr$_{14-x}$Ca$_{x}$Cu$_{24}$O$_{41}$ Andrivo Rusydi, P. Abbamonte, H. Eisaki, Y. Fujimaki, S. Uchida, G. Blumberg, M. Ruebhausen, G.A. Sawatzky The ``spin ladder'' is a reduced-dimensional analogue of the high temperature superconductors that was predicted to exhibit both superconductivity and an electronic charge density wave or ``hole crystal'' (HC). Both phenomena have been observed in the doped spin ladder system Sr$_{14- x}$Ca$_{x}$Cu$_{24}$O$_{41}$ (SCCO), which at x = 0 exhibits a HC which is commensurate at all temperatures. To investigate the effects of discommensuration we used resonant soft x-ray scattering (RSXS) to study SCCO as a function of doped hole density, $\delta $. The HC forms only with the commensurate wave vectors $L_{L}$ = 1/5 and $L_{L}$ = 1/3 (Not at 1/4!) and exhibits a simple temperature scaling $\tau _{1/3}$/ $\tau _{1/5}$ = 5/3. For incommensurate values the HC ``melts''. During this study, the distribution of holes in ladder ($n_{L})$ and chain ($n_{c})$ of SCCO are redetermined as a function of $x$ using polarization-dependence x-ray absorption spectroscopy (XAS). An interpretation of polarization dependent XAS is proposed. Based on our interpretation, for $x$ = 0, the estimation of $n_{L}$ and $n_{c}$ is 2.8 and 3.2, respectively. The number of holes in the ladder is linearly increasing with $x$. For $x$ = 11, the estimation of $n_{L}$ and $n_{c}$ is 4.4 and 1.6, respectively. This number of holes is matching well with the model of paired of holes needed to explain the RSXS result. [Preview Abstract] |
Tuesday, March 14, 2006 4:18PM - 4:30PM |
K37.00010: Shedding New Light on Spin Excitations: Magnon-Magnon Scattering in a High-T$_{c}$ Parent Compound Using Soft X-rays B. Freelon, P.G. Medaglia, A. Tebano, G. Balestrino, P.A. Glans, T.E. Learmonth, K. Smith, K. Okada, A. Kotani, D.E. Kilcoyne, B. Rude, I. Furtado, J.-H. Guo The struggle to understand high-temperature superconductivity (HTSC) has taken place in the field of condensed matter physics for a relatively long time. The difficulty in discovering a HTSC mechanism seems to originate from the confluence of two very complicated problems; electron correlation and quantum magnetism. Novel techniques that specifically probe the electronic or magnetic behavior of these materials are highly sought. We report the direct observation of spin-flip (SF) excitations using resonant inelastic soft x-ray scattering (RIXS). The antiferromganetic (AFM) charge transfer insulator, CaCuO$_{2}$, was irradiated by soft x-rays tuned to the Cu M-edge ($\sim $ 75 eV). Magnon-magnon (2 spin-flips) excitations were revealed as low-energy loss (0.39 eV) features in photon-in/photon-out experiments. The process is analogous to 2-magnon laser Raman scattering. Collected RIXS spectra provide a measurement of the 2 spin-flip excitation energy and the extraction of the AFM exchange of CaCuO$_{2.}$ These results mark the first report of two-spin-flip magneto-optical excitations revealed through Raman scattering using x-rays. This work reveals the utility of RIXS as a new probe of the spin structure in strongly correlated electron materials. [Preview Abstract] |
Tuesday, March 14, 2006 4:30PM - 4:42PM |
K37.00011: Theoretical Study of Orthorhombic Distortions in High-Temperature Superconductors Andreas Schnyder, Dirk Manske, Christopher Mudry, Manfred Sigrist Using a Fermi-liquid-based theory we calculate the response function for various spectroscopic probes in hole-doped high-T$_C$ superconductors, and determine the effects of orthorhombic distortions in the crystal lattice and asymmetry in the superconducting gap function. Employing the two-dimensional one-band Hubbard model and a generalized RPA-type theory we consider anisotropic hopping parameters ($t_x \ne t_y$) and a mixing of $d$- and $s$-wave symmetry of the superconducting order parameter. Within this model, both the electronic Raman spectra and the dynamical magnetic susceptibility~[1] are studied in detail. The relevance of these calculations to electronic Raman scattering measurements and inelastic neutron scattering experiments~[2] on untwinned YBa$_2$Cu$_3$O$_{6+x}$ are discussed. [1]~A.~P.~Schnyder, D.~Manske, C.~Mudry, and M. Sigrist, cond-mat/0510790. [2]~V.~Hinkov, S.~Pailhes, P.~Bourges, Y.~Sidis, A.~Ivanov, A.~Kulakov, C.~T.~Lin, D.~P.~Chen, C.~Bernhard, and B.~Keimer, Nature \textbf{430}, 650 (2004). [Preview Abstract] |
Tuesday, March 14, 2006 4:42PM - 4:54PM |
K37.00012: Doping dependence of the coupling of electrons to bosonic modes in the single-layer high-temperature superconductor, Bi$_{2}$Sr$_2$CuO$_{6}$ W. Meevasana, D.H. Lu, F. Baumberger, W.S. Lee, T. Cuk, J. Zaanen, Z.-X. Shen, N.J.C. Ingle, K.M. Shen, J.R. Shi, H. Eisaki, T.P. Devereaux, N. Nagaosa, S. Sahrakorpi, M. Lindroos, R. S. Markiewicz, A. Bansil A recent highlight in the study of high-T$_{c}$ superconductors is the observation of band renormalization/self-energy effects on the quasiparticles in the form of kinks in their dispersions as measured by photoemission, interpreted as signatures of collective bosonic modes coupling to the electrons. Here we compare for the first time the self-energies in an optimally doped and strongly overdoped, non-superconducting single-layer Bi-cuprate, Bi$_{2}$Sr$_2$CuO$_{6}$. Besides a strong overall weakening we also find that weight of the self-energy in the overdoped system shifts to higher energies. We present evidence that this might well be related to the coupling to c-axis phonons which are unscreened at optimal doping, being particularly sensitive to the rapid change of the c-axis screening in this doping range. We also discuss doping dependencies of the FS maps and dispersions in terms of the corresponding band structure and one-step photointensity computations. [Preview Abstract] |
Tuesday, March 14, 2006 4:54PM - 5:06PM |
K37.00013: Unusual photoemission resonances of oxygen-dopant induced states in Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ P. Richard, Z.-H. Pan, M. Neupane, Z. Wang, H. Ding, A. V. Fedorov, T. Valla, P. D. Jonhson, G. D. Gu A rising interest for the doping impurities in cuprates have been stimulated by a recent STM report on Bi$_2$Sr$_2$Ca$_1 $Cu$_2$O$_{8+x}$ [McElroy \emph{et al.}, Science \textbf{309}, 1048 (2005)], which identified oxygen dopants and investigated their local influence on the CuO$_2$ plane electronic properties. The nature of the perturbation induced by the dopants, which is of crucial importance, is thus questioned by these results. In order to investigate further this issue, we have performed an angular-resolved photoemission study of underdoped, optimally doped and overdoped Bi$_2$Sr$_2$Ca$_1 $Cu$_2$O$_{8+x}$ samples using a wide photon energy range (14 - 100 eV). We report the presence of a non-dispersive peak, which we assign to a local impurity state similar to the one observed by STM and attributed to oxygen dopants. Unusual resonances in the peak intensity are observed around 50 and 75 eV for both the nodal and anti-nodal orientations, which suggest a hybridization of the local state with in-plane Cu. [Preview Abstract] |
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