Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P33: Superconductivity: Electronic Structure II |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Goran Karapetrov, Argonne National Laboratory Room: 403 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P33.00001: Universality of momentum-dependent charge-transfer excitations in the undoped cuprates measured by resonant inelastic X-ray scattering Guillaume Chabot-Couture, Jason Hancock, Li Lu, Patrick Mang, Owen Vajk, Diego Casa, Thomas Gog, Martin Greven From its conception, the study of charge-transfer excitations in the cuprates has driven the majority of resonant inelastic X-ray scattering (RIXS) research. Still, to this day, there exists more variation among published RIXS spectra and their interpretation than common ground. By carefully studying the momentum-dependent spectral weight of three of the most important undoped cuprates -- La$_2$CuO$_4$, Nd$_2$CuO$_4$, and Sr$_2$CuO$_2$Cl$_2$ -- we present evidence of universality of the observed charge-transfer excitations. To clarify and highlight this observation, we construct dispersion diagrams and study the incident energy dependence. Comparison to Hubbard model predictions suggests that the essence of this universality is captured already by one-band physics, while material dependence and cross-sectional effects only obfuscate this behavior. [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P33.00002: Momentum-Resolved Cu K-edge RIXS Spectra in the Insulating Parent Compounds of High Tc Superconductors C-C. Chen, B. Moritz, F. Vernay, S. Johnston, J. Hancock, G. Chabot-Couture, M. Greven, I. Elfimov, G. A. Sawatzky, T.P. Devereaux Resonant inelastic X-ray scattering (RIXS) has the ability to highlight various many-body excitations that can be characterized by photon momentum transfer and energy loss. Exact Diagonalization calculations on small clusters were carried out to investigate the nature of the excitations seen in RIXS spectra in the parent compounds of high Tc superconductors. The model many-body calculation includes electronic orbitals necessary to highlight Zhang-Rice singlets, charge transfer and d-d excitations, as well as states with significant apical character. The influence of different orbitals on the RIXS spectra is studied, and the character of the excitations in different regions of the Brillouin zone is determined as well. [Preview Abstract] |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P33.00003: Momentum dependence of the electron-phonon coupling, phonon-induced pairing interaction, and self-energy effects in YBa$_2$Cu$_3$O$_7$ within the local density approximation Rolf Heid, Klaus-Peter Bohnen, Dirk Manske, Roland Zeyher Using the local density approximation (LDA) and a realistic phonon spectrum we calculate the momentum and frequency dependence of the electron-phonon coupling in YBa$_2$Cu$_3$O$_7$ and determine its consequences for the phonon-induced pairing interaction and for the electronic self-energy in the normal state. The phonon-induced interaction has a pronounced peak for large momentum transfers and the interband contributions between bonding and antibonding band are of the same magnitude as the intraband ones. The dimensionless coupling constant in the d-wave channel $\lambda^d$, relevant for superconductivity, is only 0.022, i.e., even about ten times smaller than the small value of the s-wave channel. For electronic states at the Fermi energy, the maximum in the real part of the phonon-induced self-energy at low frequencies is about a factor 5 too small compared to the experiment, resulting in a very small and smooth change in the slope of the electronic dispersion [1]. These findings suggest that phonons are not the important low-energy excitations, and cannot produce well-pronounced kinks in YBa$_2$Cu$_3$O$_7$, at least, within LDA. [1] Heid, Bohnen, Zeyher,Manske, PRL {\bf 100}, 137001 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P33.00004: Electronic Properties of Rocksalt Copper Monoxide Paul Michael Grant Rocksalt copper monoxide, although not yet synthetically realized in bulk form, can be studied computationally as a proxy for the family of layered HTSC copper oxides. We report results for a series of tetragonal CuO rocksalt structures with c/a lattice parameter ratios ranging from 1.0 to 1.5, employing the plane-wave pseudopotential method with exchange/correlation LDA+U. As expected, we obtain a metallic state for U = 0 at all values of c/a given that the nominal valence electron configuration for Cu in copper monoxides is 3d$^{9}$ yielding a partially occupied conduction band. However, completely unexpected was our finding similar metallic properties in rocksalt CuO for all physically plausible values of U (up to 10 eV) and c/a between 1.0 to approximately 1.2. Only for c/a $>$ 1.2 do our calculations reveal the opening of a Mott-Hubbard charge-transfer gap. We interpret our results$^{1}$ as supporting the original motivations of Bednorz and Mueller that high temperature superconductivity in the layered copper oxide perovskites may begin with their tendency to exhibit Jahn-Teller strong electron-phonon coupling$^{2}$. \newline $^{1}$P. M. Grant, J. Phys: CS \textbf{129} (2008) 01242. \newline $^{2}$J. G. Bednorz and K. A. Mueller, Rev. Mod. Phys. \textbf{60} (1988) 585. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P33.00005: Electronic Structure of Superconducting FeSe Studied by Photoemission Spectroscopy Rikiya Yoshida, Takanori Wakita, Hiroyuki Okazaki, Yoshikazu Mizuguchi, Shunsuke Tsuda, Yoshihiko Takano, Hiroyuki Takeya, Kazuto Hirata, Takayuki Muro, Mario Okawa, Kyoko Ishizaka, Shik Shin, Hisatomo Harima, Masaaki Hirai, Yuji Muraoka, Takayoshi Yokoya We have performed soft x-ray and ultrahigh-resolution laser photoemission measurements on tetragonal FeSe, which was recently identified as a superconductor. Energy dependent study of valence band is compared to band structure calculations and yields a reasonable assignment of partial densities of states. However, the sharp peak near the Fermi level slightly deviates from the calculated energy position, giving rise to the necessity of self-energy correction. We have also performed an ultrahigh-resolution laser photoemission experiment on FeSe and observed the suppression of intensity around the Fermi level upon cooling. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P33.00006: Generic phase diagram of ``electron-doped'' T' cuprates M. Naito, O. Matsumoto, A. Utsuki, A. Tsukada, H. Yamamoto, T. Manabe The electronic phase diagram of cuprate superconductors is a key ingredient to understand the still unresolved mechanism of high-temperature superconductivity. A particular interesting question is the differences and similarities between the hole- and electron-doped sides. The phase diagram of hole-doped high-$T_{c}$ cuprates has been well established, and shows a well-known ``dome'' shape with maximal superconductivity at a doping level of about 0.15. In contrast, the phase diagram of the electron-doped side is controversial. This is because the superconductivity in the T$'$ cuprates deteriorates seriously by the presence of impurity oxygen (O$_{ap})$ atoms, which have to be cleaned up in order to unveil the generic phase diagram of the $T'$-cuprates. We investigated the generic phase diagram of the electron doped superconductor, Nd$_{2-x}$Ce$_{x}$CuO$_{4}$, using films prepared by metal organic decomposition. After careful oxygen reduction treatment to remove interstitial O$_{ap}$ atoms, we found that the $T_{c}$ increases monotonically from 24 K to 29 K with decreasing $x$ from 0.15 to 0.00, demonstrating a quite different phase diagram from the previous bulk one. The implication of our results is discussed on the basis of tremendous influence of O$_{ap}$ ``impurities'' on superconductivity and also magnetism in T' cuprates. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P33.00007: Band-theory description of hole localization and singlet polarons in doped cuprates Alessio Filippetti, Danilo Puggioni, Vincenzo Fiorentini We use an advanced ab-initio band theory (the pseudo-self interaction corrected local density approach, pSIC) to describe spin-compensated polarons (e.g. Zhang-Rice singlets (ZRS)) typical of low-dimensional doped cuprates. Despite their many-body nature, ZRS can be transparently interpreted via (and, in fact, constructed from) single-particle states, provided that band theory describes accurately enough their localization in the limit of vanishing band dispersion. We provide examples of polarons in real materials, specifically chain-like Ca$_{2+x}$Y$_{2-x}$Cu$_{5}$O$_{10 }$and the high-T$_{c}$ superconductor (HTSC) Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{6+y}$. The former is the ideal prototype of dopable one-dimensional cuprate with zig-zag Cu-O interactions. Studying the electronic and magnetic properties over the full range of possible doping, we identify several different polaron-dominated ground states and the attendant phase transitions. Furthermore, ZRS are key to the behavior of doped CuO$_{2}$ units in HTSC. We show how their occurrence can dramatically affect the electronic properties (e.g. the Fermi surface) in underdoped Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{6+y}$. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P33.00008: Interplay of Ca and O doping in Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{6+y}$ studied by first-principles calculations Vincenzo Fiorentini, Alessio Filippetti, Danilo Puggioni Experiments reveal an impressive asymmetry in most aspects (involving e.g. magnetic, superconducting, or structural properties) of high-Tc superconductors upon cation or oxygen doping, respectively. A thorough understanding of this asymmetry cannot eschew a rigorous description of the fundamental mechanism ruling electronic and structural properties for each (x,y) doping combination. Here we present results obtained by the pseudo-self-interaction free density functional (pSIC) method, which is capable to describe metal-insulating transitions in several cuprate materials. We describe in detail the chemistry of the distinct insulating-metal transitions occurring in the CuO chains and in the CuO$_{2}$ planes in underdoped YBa$_{2}$Cu$_{3}$O$_{6+y }$for y=[0,0.5]. We then show that interactions with chains crucially affect the ability of Ca doping to inject holes in CuO$_{2}$ planes. The dramatic effects of this double-doping interplay on the magnetic and superconducting properties of underdoped Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{6+y}$ cannot be understood by the disentangled action of the individual doping sources. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P33.00009: Possible enhancements of AFM spin-fluctuations in high-T$_C$ cuprates Thomas Jarlborg Ab-initio band calculations for high-T$_C$ cuprates, together with modelling based of a free electron like band, show a strong interaction between anti-ferromagnetic (AFM) spin waves and periodic lattice distortions as for phonons, even though this type of spin-phonon coupling (SPC) is underestimated in calculations using the local density approximation. The SPC has a direct influence on the properties of the HTC cuprates and it can explain many observations. The strongest effects are seen for modulated waves in the CuO bond direction, and a band gap is formed near the X,Y points, but unusal band dispersion (like ``waterfalls'') might also be induced below the Fermi energy (E$_F$) in the diagonal direction. The band results are used to propose different ways of increasing AFM spin-fluctuations locally, and to have a higher density-of-states (DOS) at E$_F$. Static potential modulations, via periodic distribution of dopants or lattice distortions, can be tuned to increase the DOS. This opens for possibilities to enhance coupling for spin fluctuations ($\lambda_{sf}$) and superconductivity. The exchange enhancement is in general increased near a surface, which suggests a tendency towards static spin configurations. The sensivity of the band results to corrections of the local density potential are discussed. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P33.00010: Interband Transitions in La$_{2-x}$Sr$_{x}$CuO$_{4}$ observed by Resonant Inelastic X-Ray Scattering D.S. Ellis, Jungho Kim, H. Zhang, S. Wakimoto, J.P. Hill, Y. Ando, S. Komiya, D. Casa, T. Gog, Y.-J. Kim Resonant inelastic x-ray scattering measures the energy and momentum dependence of electronic excitations, whose probabilities are resonantly enhanced, in this study, by utilizing hard x-rays at the Cu K-edge absorption energy. Three main features in the resonant inelastic x-ray scattering spectrum of La$_{2-x}$Sr$_{x}$CuO$_{4}$ were observed to develop as the doping x increased from the underdoped to the overdoped region of the high-temperature superconductor phase diagram. Measured at the zone-boundary momentum transfer ($\pi $ 0), the spectra consist of three main peaks: one peak below an isosbestic point at 2.2 eV which strengthens at high doping, and two broad peaks above - one at 3.3 eV increasing in energy and decreasing in intensity, and the other stationary at higher energy. Taking a cue from existing band structure calculations, these peaks are interpreted as the transitions between stationary bands of non-bonding Oxygen, a Zhang-Rice singlet type band at the Fermi level, and the upper Hubbard band. These transitions are also discussed in the context of existing angle-resolved photoemission data. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P33.00011: Off gap interface reflectivity of electron waves in Fabry Perot resonators Aritz Leonardo, P.M. Echenique, E. Chulkov, F. Schiller, J.E. Ortega The interface reflectivity in the MgW(110) metallic quantum well is from line shape analysis of high resolution photo emission. A quick reflectivity drop is found away from projected band of the appropriate symmetry near Ef, such that the interface overcomes the bulk like quasi particle lifetime as the line broadening mechanism. A nearly free electron model for the W(110) substrate band structure demonstrates coherent wave function scattering is the relevant mechanism determines the interface reflectivity in the resonator. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P33.00012: Quasiparticle dispersion anomaly induced by the spin excitation in electron-doped cuprates Tao Zhou, Chin-Sen Ting It is proposed that the $50-70$ meV dispersion anomaly (kink) in electron-doped cuprates revealed by recent angle-resolved photoemission spectroscopy experiments is caused by coupling with the spin fluctuation. We elaborate that the kink exists both along nodal and antinodal directions, and both in the superconducting and normal state. The renormalized effect for the density of states is also studied and the hump feature outside the superconducting coherent peak is established, consistent with recent scanning tunnelling microscopy experiments. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P33.00013: Weak flux pinning in the phase separated La$_{2-x}$Sr$_{x}$CuO$_{4+y }$ system Hashini Mohottala, Barrett O. Wells, Joseph I. Budnick, William A. Hines We have studied the magnetic characteristics of a series of super-oxygenated La$_{2-x}$Sr$_{x}$CuO$_{4+y}$ samples. According to our previous studies, these samples spontaneously phase separate to give an oxygen rich superconducting phase with a T$_{C}$ near 40 K and an oxygen poor magnetic phase that also orders near 40 K.\footnote{Mohottala et al Nature Mat. 5, 377 pg. 377 (2006)} All our samples showed a large reversibility in magnetization at different temperatures. Although the internal magnetic regions were expected to behave as pinning sites, our present study shows that they do not favor flux pinning. In terms of the matching principle between the defect and the coherence length, the regions that are larger than the coherence length cannot act as flux pinning centers. Thus our results imply that the magnetic regions are too large to act as pinning centers. Overall less flux pinning in the oxygen rich system also suggests that the separate superconducting regions in the system are more homogeneous. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P33.00014: Preparation of undoped superconducting T'-\textit{RE}$_{2}$CuO$_{4}$ by MBE with ex-situ post-reduction Hideki Yamamoto, Osamu Matsumoto, Michio Naito It has recently been revealed that the optimally-reduced end-member compounds T'-\textit{RE}$_{2}$CuO$_{4}$ (\textit{RE} = Pr, Nd, Sm, Eu, Gd) show superconductivity with $T_{c}$ over 30K [1] although they are commonly believed as Mott insulators. The superconducting specimens were produced by metal organic decomposition (MOD) with elaborated reduction procedures, where the advantage of thin-films, large surface-to-volume ratio, is fully utilized to achieve the optimal oxygen configuration. Their single-crystalline thin films prepared by UHV-based process may have a further advantage of providing a good opportunity for elucidating the highly important controversy in these materials using powerful but surface-sensitive probes such as ARPES and STM. With this motivation in mind, we grew 100-nm-thick T'-\textit{RE}$_{2}$CuO$_{4}$ (\textit{RE} = Pr, Nd, Sm) films on SrTiO$_{3}$ substrates by MBE. The as-grown films were semiconducting. However, with a post-reduction treatment in a tubular furnace, which is essentially identical to that for the MOD films, the MBE films became metallic and showed superconductivity at $\sim $ 30K, indicating that the superconducting films are potentially obtainable through in-vacuo process by tuning up the reduction conditions. [1] O. Matsumoto et al., Physica C 468 (2008) 1148; M. Naito et al., J. Phys: Conf. Ser. 108 (2008) 012037. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700