Bulletin of the American Physical Society
2005 72nd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 10–12, 2005; Gainesville, FL
Session MC: Condensed Matter VI: Electron Systems |
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Chair: Pradeep Kumar, University of Florida Room: Hilton Azalea |
Saturday, November 12, 2005 8:30AM - 8:42AM |
MC.00001: Investigation of the kinetic energy change in optimally-doped and overdoped YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ Minghan Chen, D.B. Tanner, G. Hammerl, J. Mannhart Optimally-doped and overdoped thin films of the high temperature superconductor YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ (Y-123) with T$_{c }$= 90 K and 79 K, respectively, have been investigated by infrared spectroscopy. The films were highly ab-plane-oriented. In the normal state, the charge-transfer band weight is found to decrease further in the overdoped sample. This indicates the spectral weight of charge transfer band is transferred to the mid-infrared region, just as in the case of increasing doping in the under doped regime. Below T$_{c}$, the superfluid condensation is found in both optimally-doped and overdoped samples. In the optimally-doped sample, the kinetic energy does not change significantly. However, in comparison to the optimally-doped sample, the overdoped sample shows much smaller superfluid (or condensate) density . This result indicates it is difficult to decide the kinetic energy change in the overdoped samples. [Preview Abstract] |
Saturday, November 12, 2005 8:42AM - 8:54AM |
MC.00002: Field and Temperature Dependent Transmission of Pr$_{2-x}$Ce$_{x}$CuO$_{4}$ Naveen Margankunte, David Tanner, Alexandre Zimmers, Richard Greene, Yong-Jie Wang We report mid-infrared transmission measurements of electron doped Pr$_{2-x}$Ce$_{x}$CuO$_{4 }$(PCCO) thin films for a wide range of dopings, in the large energy pseudogap regime both as a function of temperature and magnetic field. While there are large temperature dependent changes (indicative of the formation of the pseudogap) in the underdoped regime, a magnetic field up to 30 T does not induce any change in transmission within the experimental signal to noise resolution. [Preview Abstract] |
Saturday, November 12, 2005 8:54AM - 9:06AM |
MC.00003: The phase diagram of (La$_{1-y}$Pr$_{y})_{1-x}$Ca$_{x}$MnO$_{3}$ where x=0.33 and y=0.25, 0.5 and 0.75. Tara Dhakal, Jacob Tosado, Amlan Biswas The manganites have the chemical formula R$_{1-x}$A$_{x}$MnO$_{3}$ where R is a rare earth ion like La, Pr, Nd etc. and A a divalent ion like Ca, Sr, Pb etc.. These materials are known for their colossal magneto resistive (CMR) property and metal to insulator phase transition. Certain compositions of these manganites also show mixed phases of charge ordered insulator (COI) and ferromagnetic metal (FMM). It has been seen that these phases are flexible i.e. they can move around or grow in size by the application of external bias voltage, magnetic field or temperature. One of such materials is (La$_{0.5}$Pr$_{0.5})_{0.67}$Ca$_{0.33}$MnO$_{3}$. To understand the dynamics of the local phase, we have measured a phase diagram of this material. To obtain the phase diagram we first measured resistance (R) as a function of magnetic field (H) of the material at several fixed temperatures. The resistance vs field graph shows hysteretic behavior- a sign of coexistence of both COI and FMM phases. The phase diagram shows 3 regions, namely COI state, mixed phase state and FMM state. An interesting part of this phase diagram is that even in the percolated metallic state, there is still significant COI material present which gives rise to a third phase boundary which resembles the phase diagram of Pr$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (PCMO) ( Amlan Biswas et al. Phys. Rev. B 63, 184424 (2001)). [Preview Abstract] |
Saturday, November 12, 2005 9:06AM - 9:18AM |
MC.00004: Glassy Behavior of Interface States in Al-AlOx-Al Tunnel Junctions Jeremy Nesbitt, Arthur Hebard We present results of a study of tunnel junction aging in which early time dynamics are captured by in situ monitoring of electrical properties of Al-AlOx-Al planar tunnel junctions beginning when the deposition of the counterelectrode is complete. The observed stretched exponential dependences of the conductance and the capacitance manifest hierarchically constrained dynamics imposed by correlated relaxations of interface traps. Bias voltage is used as a control parameter to create bias-dependent lifelines that exhibit memory and age-dependent relaxations. Simple tunnel barrier and equivalent circuit modeling provide a comprehensive understanding of this novel glassy behavior in tunnel junctions. This work is supported by NSF under contract DMR 0404962 [Preview Abstract] |
Saturday, November 12, 2005 9:18AM - 9:30AM |
MC.00005: Magnetic properties of Rb$_{j}$Co$_{4}$[Fe(CN)$_{6}$]$_{k}$$\cdot$$n$H$_{2}$O Prussian blue nanoparticles N.E. Anderson, J.-H. Park, M.W. Meisel, J. Long, F. Frye, D.R. Talham Magneto-optically active Prussian blue materials are of considerable interest because of their many possible applications.\footnote{J.-H. Park, E. {C}i\v{z}m\'{a}r, M. W. Meisel, Y. D. Huh, F. Frye, S. Lane, and D. R. Talham, Appl. Phys. Lett. \textbf{85}, 3797 (2004).} Nanoparticles of Rb$_{j}$Co$_{4}$[Fe(CN)$_{6}$]$_{k}$$\cdot$$n$H$_{2}$O have been synthesized, and TEM images indicate that clusters of 5 nm particles were obtained. Futhermore, the particles appear to show weak photo-induced effects similar to those reported in bulk materials. Here, we present preliminary data to illustrate the magnetic characteristics of these new materials. \linebreak J. Long was a NSF-REU participant (NSF CHE-0353828). [Preview Abstract] |
Saturday, November 12, 2005 9:30AM - 9:42AM |
MC.00006: Electron Correlation and Charge Transfer in (Ba$_{0.9}$Nd$_{0.1})$CuO$_{2+\delta }$/(CaCuO$_{2})_{2 }$Superconducting Superlattices B. Freelon, J.-H. Guo, Andreas Augustsson, P. G. Medaglia, A. Tebano, G. Balestrino The mechanism of high-temperature superconductivity (HTSC) among cuprates is still highly controversial. Although it is widely accepted that HTSC occurs primarily within Cu-O planes of cuprates, there is contention concerning the low-energy physics of these planes. It was recognized shortly after the discovery of HTSC that the fundamental planar character of superconducting superlattices (SL) could be used to investigate the physics of atomic planes in HTSC compounds. Using the artificial 2$\times $2 HTSC SL (Ba$_{0.9}$Nd$_{0.1}$CuO$_{2+x})_{2}$/(CaCuO$_{2})_{2}$, we investigate in-plane CuO$_{2}$ physics by applying x-ray emission/absorption spectroscopy. The superlattices are fabricated by pulsed-laser deposited molecular beam epitaxy (MBE) in an atomic layer-by-layer fashion.$^{i}$ (Ba$_{0.9}$Nd$_{0.1}$CuO$_{2+x})_{2}$/(CaCuO$_{2})_{2 }$consists of two layers. Each layer, separately, being an insulator. By alternately depositing the insulators, superlattices exhibiting a T$c$ of 80K can be fabricated. It has been shown that superconduction occurs exclusively within the infinite layer (IL) and not the charge reservoir$^{ii}$ (CR)of the superlattices. We demonstrate resonant x-ray emission and absorption to be insightful tools for studying the IL, CR and superlattice structures. We measure the O 1s density of state to be insulating for the component layers and metallic for the superlattice. Using resonant inelastic scattering (RIXS) we make the first direct observation of Zhang-Rice singlets in artificial high-temperature superconducting heteroepitaxial structures. Such low-energy singlets are thought to give rise to the superconducting state. A comparison of the x-ray emission spectra of the superlattice and its component layers gives evidence of charge transport from the so-called charge reservoir layer to the superconducting infinite layer. $^{i }$G. Balestrino, S. Lavanga, P. G. Medaglia, P. Origiani, A. Paoletti, G. Pasquini, A. Tebano, and A. Tucciarone, Appl. Phys. Lett. \textbf{79}, 99 (2001). $^{ii }$G. Balestrino, P. G. Medaglia, P. Origiana, A. Tebano, C. Aruta, S. Lavanga, and A. A. Varlamov, Phys. Rev. Lett. \textbf{89,} 156402 (2002). [Preview Abstract] |
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