Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session P38: Superconductivity-Optical Spectroscopy of Cuprates |
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Sponsoring Units: DCMP Chair: Tomas Timusk, McMaster University Room: Baltimore Convention Center 341 |
Wednesday, March 15, 2006 11:15AM - 11:27AM |
P38.00001: Optical Study of Optimally Doped and Overdoped YBCO Minghan Chen, D.B. Tanner, G. Hammerl, J. Mannhart Thin films of the optimally-doped and overdoped high temperature superconductor (YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ and Y$_{0.7}$Ca$_{0.3}$Ba$_{2}$Cu$_{3}$O$_{7-\delta }$ with T$_{c }$= 90 K and 79 K, respectively) have been investigated by optical spectroscopy in the ab-plane. In the normal state, with increasing the carrier concentration in the CuO$_{2}$ planes, spectral weight is lost in the high-frequency charge-transfer band and transferred to lower frequencies. With increased doping, the free-carrier (Drude-like component) plasma frequency increases, consistent with a charge density increase. However, the superfluid density decreases in this regime (overdoped region) and a substantial normal-fluid component still exists in the low frequency part of the optical conductivity well below $T_{c}$. [Preview Abstract] |
Wednesday, March 15, 2006 11:27AM - 11:39AM |
P38.00002: The optical conductivity of Ortho II YBa$_2$Cu$_3$O$_{6.5}$. Thomas Timusk, Jung-Seek Hwang, Jing Yang, Sergei Sharapov, Jules Carbotte, Doug Bonn, Ruixing Liang, Walter Hardy The a-axis optical properties of the ortho II phase of YBCO (every other chain filled, $T_c$= 59 K) were derived from reflectance data over a wide frequency and temperature range. Above 200 K the spectra are dominated by a broad background of scattering that extends to 1 eV. Below 200 K, in the normal state, a shoulder in the reflectance signals the onset of scattering at 400 cm$^{-1}$. Below the superconducting transition temperature the superconducting condensate appears. Its spectral weight is consistent, to within experimental error, with the FGT sum rule and with independent measurements of Gd ESR. We also compare our data with magnetic neutron scattering on samples from the same source that show a strong resonance at 31 meV. Extrapolating the optical conductivity to zero frequency yields the dc resistivity of Ortho II which is in good agreement with four-probe measurements. We find that the scattering rates can be modeled as the combined effect of the neutron resonance, a bosonic background and a density of states with a pseudogap. [Preview Abstract] |
Wednesday, March 15, 2006 11:39AM - 11:51AM |
P38.00003: Optical conductivity of Bi$_2$Sr$_2$CuO$_6$ in the optimally and overdoped regimes R.P.S.M. Lobo, D. Lyzwa, N. Bontemps, Z.Z. Li, H. Raffy Bi$_2$Sr$_2$CuO$_6$ has a much lower critical temperature ($T_c^{Max} \sim 20$ K) than other single layer cuprate superconductors, making this compound very useful to investigate normal state properties of cuprates. In addition, it is possible to oxygenate this material to a relatively high degree of overdoping ($T_c < 5$ K). We measured, from room temperature to 5 K, the optical conductivity of the same Bi$_2$Sr$_2$CuO$_6$ film thermally treated to be in the optimally and overdoped regimes. The in-plane resistivity in the optimally doped regime depends lineraly on the temperature. It develops a positive curvature in the overdoped regime as expected from its more Fermi liquid like behavior. Surprisingly, despite its linear resistivity, the frequency dependent scattering rate in the optimally doped sample has a quadratic behavior. We will discuss our results in terms of the possible scenarios for the normal state conductivity and infer its effects on the superconducting state. [Preview Abstract] |
Wednesday, March 15, 2006 11:51AM - 12:03PM |
P38.00004: Doping and temperature dependent optical properties of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ Jungseek Hwang, Thomas Timusk, Genda Gu, Martin Greven, Hiroshi Eisaki We report on the ab-plane reflectance of underdoped (UD), optimally doped (OPT), and overdoped (OD) Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+{\delta}}$ (Bi-2212) samples [$T_{c}$ = 69 K(UD), 96 K (OPT), 82 K (OD), 80 K (OD: annealed from the OPT sample), 65 K (OD) and 60 K (OD)]. We analyzed the measured reflectance data and previous data of two underdoped Bi-2212 samples ($T_c$ = 67 K (UD) and 82 K (UD)) to extract the doping dependent optical constants. Bi-2212 is one of the most important cuprate systems widely studied by ARPES and tunnelling. We also calculate the doping dependent dc resistivity from extrapolation of the optical conductivity and the doping dependent superfluid density and the optical self- energy by using the extended Drude model. With these quantities in hand, we will discuss some current issues: the kinetic energy change at $T_c$, the role of the magnetic resonance mode, and a possible quantum critical point. [Preview Abstract] |
Wednesday, March 15, 2006 12:03PM - 12:15PM |
P38.00005: Polarization dependence of charge-transfer excitations in La$_2$CuO$_4$ Li Lu, Guillaume Chabot-Couture, Jason Hancock, Owen Vajk, Guichuan Yu, Kenji Ishii, Jun'ichiro Mizuki, Diego Casa, Thomas Gog, Martin Greven We have carried out an extensive resonant inelastic x-ray scattering (RIXS) study of La$_2$CuO$_4$ at the Cu K-edge. Multiple charge-transfer excitations have been identified using the incident photon energy dependence of the cross section and studied carefully with polarizations E//c and E //ab. An analysis of the incident photon energy dependence, the polarization dependence, as well as the K-edge absorption spectra, indicates that the RIXS spectra reveal rich physics about the K-edge absorption process and momentum-dependent charge-transfer excitations in cuprates. [Preview Abstract] |
Wednesday, March 15, 2006 12:15PM - 12:27PM |
P38.00006: Evidence of an anisotropic charge-excitation gap in stripe-ordered \boldmath La$_{2-x}$Ba$_x$CuO$_4$ with $x=1/8$ \unboldmath C. C. Homes, S. V. Dordevic, G. D. Gu, Q. Li, T. Valla, J. M. Tranquada The {\it ab}-plane optical properties of a cleaved single crystal of La$_{2-x}$Ba$_x$CuO$_4$ for $x=1/8$ ($T_c \simeq 2.4$~K) have been measured over a wide frequency and temperature range. The low-frequency conductivity is Drude-like and shows a metallic response with decreasing temperature. However, below $\simeq 60$~K, corresponding to the onset of charge-stripe order, there is a rapid loss of spectral weight below about 40~meV, resulting in a major reduction in the number of free carriers. This suggests a partial gapping of the Fermi surface. Surprisingly, the sample is still metallic and becomes a superconductor at low temperature. This material is a striking example of how charge and spin stripe order, metallic behavior and superconductivity can coexist. [Preview Abstract] |
Wednesday, March 15, 2006 12:27PM - 12:39PM |
P38.00007: Anisotropic Drude response in Mg(B$_{1-x}$C$_{x})_{2}$ Teruhisa Kakeshita, Sergey Lee, Setsuko Tajima There exists an unsolved issue on MgB$_{2}$ that a plasma edge estimated from optical spectra so far is conspicuously inconsistent with a band calculation. It is mysterious since experimental band dispersions by ARPES are marvelously coincident with the band calculation. We report on a- and c-axis optical responses in Mg(B$_{1-x}$C$_{x})_{2 }$ using small single crystals and a FTIR spectrometer combined with an optical microscope. It was verified that the Drude responses show the anisotropy between a- and c-axis. The observed plasma frequencies $\omega_{p'}$ are considerably small compared to a theoretical value ($\sim $7eV), whereas the bare ones $\omega _p $, estimated from a sum rule of optical conductivity $\int {d\omega \sigma (\omega )=(\pi /2)\omega _p^2 } =(\pi /2)\varepsilon _\infty \omega _p^{'2} $, are fairly coincident with it. We also discuss an effect of carbon-substitution on carrier concentration and scattering rate in a multiband system. This work was supported by the New Energy and Industrial TechnologyDevelopment Organization(NEDO) through ISTEC as the Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications. [Preview Abstract] |
Wednesday, March 15, 2006 12:39PM - 12:51PM |
P38.00008: Mode coupling effect in infrared spectra of Tl$_2$Ba$_2$Ca$_{n-1}$Cu$_n$O$_x$ (n=1, 2, 3) N.L. Wang, Y.C. Ma We performed in-plane optical reflectance measurements on Tl$_2$Ba$_2$Ca$_{n-1}$Cu$_n$O$_x$ with n=1, 2, 3. The single crystals were successfully grown by flux method with maximum T$_c$=90 K, 109 K, and 119 K for n=1, 2, 3, respectively. For all three phases near optimal doping, the reflectance roughly has a linear-frequency dependence in the normal state, but displays a pronounced knee structure followed by a dip-like feature at higher frequency below T$_c$. Such characteristic features were commonly ascribed to the coupling of electrons with a bosonic mode. Very remarkably, we found that the energy levels of those features scale with T$_{c}$ for the three phases. The results suggest against a phonon origin for the bosonic mode. We also investigated the spectral evolution with doping for Tl-2201 crystals in the overdoped side. We found that the mode coupling effect weakens with doping and disappears in the heavily overdoped sample. Meanwhile, the optical scattering rate evolves from a linear- $\omega$ dependence to a shape with upward curvature in the normal state. Both the temperature and frequency dependence of the scattering rate can be described by a power law relation. Compared with ARPES results, we suggest that the overall decrease of the scattering rate may mainly originate from the increase of the quasiparticle life time near the ($\pi$,0) region in the Fermi surface. [Preview Abstract] |
Wednesday, March 15, 2006 12:51PM - 1:03PM |
P38.00009: A Complete Charge Model For The High T$_{c}$ Superconductivity Young Hoon Kim, Pei Herng Hor Focusing on the recent transport, far-infrared (far-IR), and neutron scattering data, we establish a model for the high temperature superconductivity (HTS) built on the two-dimensional (2D) square electronic lattices in the CuO$_{2}$ planes and their three-dimensional ordering. We demonstrate that our model captures all the essential physics that bring about a coherent picture of the HTS and offers the key to the mechanism for the HTS. [Preview Abstract] |
Wednesday, March 15, 2006 1:03PM - 1:15PM |
P38.00010: Temperature Dependent of the Optical Spectral Weight in Correlated Metal Nd$_{1-x}$TiO$_{3 }$(x=0.095) Jing Yang, Jungseek Hwang, Thomas Timusk, Athena Safa-Sefat, John E. Greedan We investigated the infrared reflectance of Nd$_{1-x}$TiO$_{3}$, which is a hole-doped transition-metal-oxide system. In the metallic sample with $x$=0.095 (hole concentration=3$x$=0.285), the partial optical spectral weight, $\omega (\Omega ,T)=\int_0^\Omega {\sigma _1 (\omega ,T)d\omega } $, turns out to be a linear function of $T^{2 }$at different cutoff frequencies. Recent optical studies of LSCO [1] and BSCCO [2] also found that the optical spectral weight varies quadratically with temperature, i.e. $\omega (\Omega ,T)\simeq \omega _0 -B(\Omega )T^2$, in both superconductors and nonsuperconducting metals. The coefficient $B(\Omega )$ was considered as a ``thermal response'' of the carriers. In our study, for Nd$_{1-x}$TiO$_{3 }(x$=0.095), $B(\Omega )$ exhibits distinct features which we compare to both cuprates and conventional metals. [1] M. Ortolani \textit{et al}., Phys. Rev. Lett. \textbf{94}, 067002 (2005). [2] H. J. A. Molegraaf \textit{et al}., Science \textbf{295}, 2239 (2002). [Preview Abstract] |
Wednesday, March 15, 2006 1:15PM - 1:27PM |
P38.00011: Phonon Shifts at the Superconducting Transition in \textit{$\kappa $}-(BEDT-TTF)$_{2}$-Cu(NCS)$_{2}$ C. N. Kodituwakku, C. A. Burns, X. Wang, H. Sinn, A. Said, A. Alatas, H.H. Wang, U. Gaeiser, J.A. Schlueter We have measured the phonon spectra above and below the superconducting transition in \textit{$\kappa $}-(BEDT-TTF)$_{2}$-Cu(NCS)$_{2}$. This organic superconductor has a transition temperature near 10K. These measurements were carried out using inelastic x-ray scattering at sector 3ID at the Advanced Photon Source. The incident x-ray energy was 21.657 keV and the resolution of the spectrometer was about 2.0 meV. We have observed significant phonon shifts at several energies in these spectra at several points in the Brillouin zone. Here we discuss the behavior of the phonons and possible reasons for the shifts. [Preview Abstract] |
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