Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Y11: Oxide Spectroscopy |
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Sponsoring Units: DCMP Chair: J. Steven Dodge, Simon Fraser University Room: Morial Convention Center RO9 |
Friday, March 14, 2008 11:15AM - 11:27AM |
Y11.00001: Transient Grating Measurements of YBa$_{2}$Cu$_{3}$O$_{7-x}$ films C.L.S. Kantner, J.D. Koralek, I. Hetel, T.R. Lemberger, J. Orenstein Transient photoinduced changes in the transmission of YBa$_{2}$Cu$_{3}$O$_{7-x}$ thin films have been measured using the charge-grating technique. In this technique two non-collinear pulses are interfered to create a sinusoidal spatial variation in superfluid density, which leads to a grating in the transmission coefficient. Evolution of the amplitude and phase of this grating in the time-domain can be monitored by the coherent detection of a time-delayed diffracted probe pulse. Previous experiments using conventional pump-probe methods have revealed at least two components in the change in transmission. Resolving these components is inherently ambiguous as their relative phase is undetermined. We report on the use of the phase sensitivity of the transient grating experiment to separate the individual components of the two-component wave form. [Preview Abstract] |
Friday, March 14, 2008 11:27AM - 11:39AM |
Y11.00002: Visible-pump, THz-probe measurement of the photocarrier mobility in an undoped cuprate Jesse Petersen, J. Steven Dodge, Ruixing Liang We present new experimental results on the mobility of photoexcited carriers in Sr$_2$CuCl$_2$O$_2$, an undoped cuprate. We use ultrafast laser pulses to excite photocarriers in the antiferromagnetic insulating lattice. We then probe the low-frequency dynamical conductivity of the resulting nonequilibrium state with time-domain terahertz spectroscopy. We observe the prompt onset of photoconductivity followed by a non-exponential decay on ps timescales. Assuming all photoexcited carriers are free we observe a peak mobility of $\sim$0.1 cm$^2$/Vs, much lower than the Hall mobility in chemically doped systems with similar carrier concentrations \footnote{Y. Ando {\em et al.} PRL {\bf 87} 017001 (2001)}. Such a low mobility suggests the formation of polarons or excitons after photoexcitation. We will also discuss the temperature dependence of the nonequilibrium state. [Preview Abstract] |
Friday, March 14, 2008 11:39AM - 11:51AM |
Y11.00003: Time-resolved spectroscopy of the charge-transfer gap in Sr$_2$CuO$_2$Cl$_2$ J. Steven Dodge, Andreas Schumacher, Lance Miller, Daniel Chemla We present energy- and time-resolved pump-probe spectroscopy near the charge-transfer gap in the undoped cuprate compound Sr$_2$CuO$_2$Cl$_2$. Upon photoexcitation, an increase in absorption is observed for energies below 1.95~eV, whereas a decrease occurs above 1.95~eV. Overall, the spectral weight is not conserved over the probe range of 1.6-2.3 eV. No hole-burning is observable at the pump energy $E_{\mathrm{pump}} = 2.1$~eV. The transient spectral changes appear as one spectral unit instantaneously after the excitation, and they decay, again as one spectral unit, on a picosecond time scale. The photoinduced response relates simply to the thermal response, indicating a common boson-mediated origin. These results support a theoretical model that places the gap energy near 1.5 eV, well below the peak in the charge-transfer absorption spectrum.\footnote{K. M. Shen \textit{et al.}, Phys.~Rev.~B \textbf{75}, 075115 (2007).} In this model, the photoexcited state decays rapidly to the gap energy via phonon emission, and the presence of the additional phonons then has the same effect on the charge-transfer absorption as an increase in the equilibrium lattice temperature. [Preview Abstract] |
Friday, March 14, 2008 11:51AM - 12:03PM |
Y11.00004: Unusual Spectral Signatures in Na-doped Oxychloride High Temperature Superconductors M. Brunner, K.-H. Kim, H.-G. Lee, S.-I. Lee, M.R. Peterson, B.S. Shastry, G.-H. Gweon Electron spectroscopy studies on Na-doped oxychloride samples (Na-CCOC; (NaCa)$_2$CuO$_2$Cl$_2$) have received much attention recently, due to the facts that Na-CCOC samples are easy to cleave, the crystal structure is relatively simple among the cuprates, and the spectroscopy reveals enhanced signatures of putative ``competing order.'' Here, we report the electronic structure of Na-CCOC investigated by angle resolved photoelectron spectroscopy (ARPES) as a function of momentum, energy and doping, with an emphasis on unusual nature of some signatures clearly observed in this family of the cuprates. We discuss those signatures in relation to the recently discovered high energy dispersion anomaly and the suggested charge order. [Preview Abstract] |
Friday, March 14, 2008 12:03PM - 12:15PM |
Y11.00005: Competition scenario in Raman and ARPES experiments in electron-doped cuprates Belen Valenzuela, Elena Bascones Raman and ARPES experiments in the superconducting state of electron doped cuprates have shown deviations from the predictions of a monotonic d-wave superconducting gap. Two scenarios have been proposed to explain these experiments: a non-monotonic BCS gap on a large Fermi surface and a two band model due to the truncation of the Fermi surface by antiferromatic correlations. We calculate angle resolved photoemision spectrum and Raman signal in the superconducting phase using a two-band model where superconductivity and antiferromagnetism competes and compare our results with others theoretical scenarios. We also discuss the effect of the non-monotonicity of the gap on the tunneling experiments. [Preview Abstract] |
Friday, March 14, 2008 12:15PM - 12:27PM |
Y11.00006: Appearance of Universal Metallic Dispersion in a Doped Mott Insulator Hsin Lin, S. Sahrakorpi, R.S. Markiewicz, M. Lindroos, X.J. Zhou, T. Yoshida, W.L. Yang, T. Kakeshita, H. Eisaki, S. Uchida, Seiki Komiya, Yoichi Ando, F. Zhou, Z.X. Zhao, T. Sasagawa, A. Fujimori, Z. Hussain, Z.-X. Shen, A. Bansil Under strong electronic correlations the parent compounds of all cuprate high-temperature superconductors assume the so-called Mott-Hubbard insulating state. By what routes these insulators accomplish the miraculous transformation into superconductors with the addition of electrons or holes is a question of intense current interest. In this study we consider the classic superconductor La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) over the wide doping range of $x=0.03-0.30$, delineating how the electronic spectrum evolves with doping for binding energies extending to several hundred meV's. Our analysis indicates that this Mott insulator contains `nascent' or `preformed' metallic states, which develop finite spectral weight with doping, but otherwise undergo relatively little change in dispersion over a wide doping range. Our findings challenge existing theoretical scenarios for cuprates. Work supported in part by the USDOE. [Preview Abstract] |
Friday, March 14, 2008 12:27PM - 12:39PM |
Y11.00007: Systematic ARPES study of Ln$_x$Bi$_2$Sr$_{2-x}$CuO$_{6+\delta}$ Zhihui Pan, Madhab Neupane, Yiming Xu, Ziqiang Wang, Huiqian Luo, Lei Fang, Haihu Wen, Hong Ding Ln$_{x}$Bi$_{2}$Sr$_{2-x}$CuO$_{6+\delta}$ is a good candidate to investigate the effects of charge doping and potential disorder to the properties of the high-Tc cuprates. The samples with different Ln elements exhibits very different property, and can used as a probe to study the superconductivity with different Ln substitutions. High-quality single crystals of Ln$_{x}$Bi$_{2}$Sr$_{2-x}$CuO$_{6+\delta}$(Bi and La) have been synthesized over a wide substitution range. We will report our high-resolution ARPES results on of Ln$_{x}$Bi$_{2}$Sr$_{2-x}$CuO$_{6+\delta}$. [Preview Abstract] |
Friday, March 14, 2008 12:39PM - 12:51PM |
Y11.00008: Strong correlation effects in the electron momentum density distribution of La$_{2-x}$Sr$_x$CuO$_4$ B. Barbiellini, P.E. Mijnarends, S. Kaprzyk, R.S. Markiewicz , M. Itou, Y. Sakurai, K. Yamada, A. Bansil Compton scattering offers unique capabilities for measuring absolute spectral weights, which are not obtainable by other spectroscopies. Moreover, this technique is genuinely a bulk- sensitive probe. In this connection, we have carried out a series of high resolution Compton scattering measurements on oriented single crystals of La$_{2-x}$Sr$_x$CuO$_4$ at three different dopings x=0, 0.15 and 0.30, together with corresponding computations based on the LDA and on models for treating strong correlation effects. Theoretical predictions are compared and contrasted with the experimentally reconstructed two-dimensional electron momentum densities to identify strong correlation effects in the spectra, and to delineate how these effects evolve as the system undergoes the transition from the Mott insulator to the superconductor. Work supported in part by the USDOE. [Preview Abstract] |
Friday, March 14, 2008 12:51PM - 1:03PM |
Y11.00009: New analysis of the electronic excitations in the Mott insulator Nd$_2$CuO$_4$ using momentum-dependent intensity maps Guillaume Chabot-Couture, Jason N. Hancock, Diego M. Casa, Patrick K. Mang, Thomas Gog, Martin Greven Resonant inelastic X-ray scattering (RIXS) is a rapidly advancing technique that allows the measurement of electronic excitations in correlated-electron systems. In order to extend this technique, we developed a new circle to perform azimuthal rotations of the crystal. This allowed us to perform precise measurements of the electronic excitations as a function of the momentum transfer in the copper-oxygen planes and the incident photon polarization. As a result, we discovered that Cu K edge RIXS is at most weakly polarization dependent when the polarization is kept in the copper-oxygen planes. We used this new circle to determine the intensity variations of different energy-loss excitations across many Brillouin zones. These intensity maps as well as inelastic spectra measured at high-symmetry points in the Brillouin zone allow an improved analysis of the electronic-excitation spectral weight in this material. We discuss our findings in the context of past measurements on other cuprate systems. [Preview Abstract] |
Friday, March 14, 2008 1:03PM - 1:15PM |
Y11.00010: Valence Electronic Structure of YBCO Probed by X-ray Standing Waves Jorg Zegenhagen, Sebastian Thiess, Tien-Lin Lee, Carmela Aruta, Chengtian Lin, Federica Venturini, Nicholas Brookes, Bruce C.C. Cowie The photoelectron emission spectrum of the valence band of the high-temperature superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) in the X-ray regime is dominated by contributions from the copper sites (d states) because of the comparably large cross section. With the help of the x-ray standing wave (XSW) technique in combination with photoelectron spectroscopy, it is possible to separate the contributions to the valence band originating from different lattice sites, even if they are populated by the same element. In this way, by applying the XSW method with photoelectron spectroscopy, we discriminated the contributions to the YBCO valence band coming from the nonequivalent in-plane and chain copper sites. Within the resolution of our measurements, the contributions of Cu-I and Cu-II to the valence band were found to be identical. [Preview Abstract] |
Friday, March 14, 2008 1:15PM - 1:27PM |
Y11.00011: Doping Dependence of Electronic Excitations in La$_{2-x}$Sr$_{x}$CuO$_{4}$ Observed by K-edge RIXS D.S. Ellis, Jungho Kim, J.P. Hill, S. Wakimoto, R.J. Birgeneau, T. Gog, D. Casa, Y.-J. Kim Resonant inelastic xray scattering (RIXS) spectra of the cuprate La$_{2-x}$Sr$_{x}$CuO$_{4 }$are measured for single crystal samples with progressively larger value of x, ranging from undoped to the overdoped regime. As x is increased in the underdoped region, the lowest energy excitation above the charge transfer gap is sharply suppressed, but many of the general spectral features and overall spectral weight distribution above the gap do not appreciably change, and the broad intensity around the same energy of the exciton remains constant. As the sample becomes overdoped, a much more pronounced change of the spectral weight above the charge transfer gap occurs. An in-gap state at $\sim $1.8 eV in the undoped case, which shows no dispersion with momentum, broadens and shifts down in energy as the doping is increased. The amount of the observed shift is to within an order of magnitude of the change calculated from simple crystal field model. . [Preview Abstract] |
Friday, March 14, 2008 1:27PM - 1:39PM |
Y11.00012: Charge superstructures in Zn-doped La$_{2-x}$Sr$_x$CuO$_4$ J. C. Lee, A. Rusydi, S. Smadici, S. Wang, P. Abbamonte, M. Enoki, M. Fujita, M. Ruebhausen, K. Yamada We have observed valence band charge order in both twinned and untwinned samples of La$_{1.95}$Sr$_{0.05}$Cu$_{0.95}$Zn$_{0.05} $O$_{4}$ with resonant soft x-ray scattering. In the untwinned sample the order was observed to be mainly electronic and centered at the (0,0.084,2)$_o$ position in reciprocal space, indicating diagonal charge order with period $12 a_o$, where $a_o$ is the orthorhombic lattice parameter. This order has approximately half the wavelength of the magnetic order previsouly observed with neutron scattering* in this system, suggesting a stripe interpretation. Preliminary measurements on a twinned sample revealed four satellites at (0,$K$,2)$_o$, where $K$ takes on integer multiples of the value 0.011. Relationships between these effects and the crystal structure of La$_{1.95}$Sr$_{0.05}$Cu$_{0.95}$Zn$_{0.05}$O$_{4}$ will be discussed. *M. Matsuda, et. al., Phys. Rev. B {\bf 73}, 140503(R) (2006) [Preview Abstract] |
Friday, March 14, 2008 1:39PM - 1:51PM |
Y11.00013: The model high-T$_C$ superconductor HgBa$_2$CuO$_{4+\delta}$: a quantitative annealing, transport and magnetic susceptibility study Neven Barisic, Yuan Li, Guillaume Chabot-Couture, Yu Guichuan, Yongchan Cho, Xudong Zhao, Martin Greven The investigation of the physical properties of high-T$_C$ superconductors (HTSCs) is complicated by several materials-related obstacles. In order to obtain reliable experimental results, homogeneous single crystals are needed, which are difficult to obtain due to chemical and/or electronic disorder. HgBa$_2$CuO$_{4+\delta}$ (Hg1201) is a particularly interesting HTSC, since it possesses the highest superconducting transition temperature (T$_C$=97 K) among single Cu-O layer compounds, a simple crystal structure, and the property to confine disorder relatively far a way from the superconducting pivotal Cu-O layers. Recently, we reported a new recipe for the growth of unprecedentedly large, gram-sized monocrystals of Hg1201 [1]. Here, we demonstrate that it is possible to select samples of the highest quality, with very few vortex pinning centers, and to dope them uniformly over a wide range of hole concentration. Furthermore, we show that those crystals can be cleaved and contacted with high-quality electrical contacts. These results make Hg1201 a particularly interesting model system for extensive experimental investigation. [1] X. Zhao et al., Adv. Mater. 18, 3243 (2006) [Preview Abstract] |
Friday, March 14, 2008 1:51PM - 2:03PM |
Y11.00014: ABSTRACT WITHDRAWN |
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