Bulletin of the American Physical Society
2012 Annual Meeting of the California-Nevada Section of the APS
Volume 57, Number 13
Friday–Saturday, November 2–3, 2012; San Luis Obispo, California
Session H4: Condensed Matter IV: Atoms and Molecules |
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Chair: Michael Peterson, California State University, Long Beach Room: Business 003 0113 |
Saturday, November 3, 2012 2:00PM - 2:12PM |
H4.00001: Possible Quantum Transport in (RE)Ba$_{2}$Cu$_{3}$O$_{7-y}$ Perovskites Paul Grant For y $\approx $ 0, the crystal structure of the ``1-2-3'' family of rare earth perovskites displays a curious ``porosity'' feature, namely, along the b-axis direction of a region usually termed the ``CuO chains,'' one observes a dramatically wide ``channel'' bounded within a Ba-Cu-O tube. The cross-sectional area of these channels is roughly that of a single-wall carbon nanotube, suggesting the former may manifest Buettiker-Landauer quantum conductance similar to that observed in the latter. Moreover, by employing various ratios of Pr/Y for the RE component of the host system, the bulk electrical properties of the surrounding host can be tailored from completely insulating to metallic. We test our conjecture predicting ballistic transport down the ``Ba-Cu-O channel'' using density functional theory and report our initial findings here. We also discuss possible experimental embodiments which could lead to nano-controllable gate structures. [Preview Abstract] |
Saturday, November 3, 2012 2:12PM - 2:24PM |
H4.00002: Magneto Optical Kerr Effect Measurement of Double Exchange Spring System Hanming Yuan, Jiyeong Gu Magnetic property of the symmetric Double Exchange Spring System, soft(S)/hard(H)/soft(S) magnetic layers Glass/NiFe (bottom Py)/SmFe/NiFe (top Py), was investigated using Magneto Optical Kerr Effect (MOKE) measurement. In order to produce a symmetric non-collinearity in magnetization, the thicknesses of the two Py layers are controlled to be the same during the deposition. Due to the finite skin depth of the laser used in MOKE measurement magnetic hysteresis loop for each Py layer can be measured separately by adjusting the right thickness of the layers. First of all, we found the magnetic hysteresis loops for the bottom and the top Py layers are not the same. Moreover, we found that the coercivity of the bottom Py measured from MOKE is closer to the coercivity of the first switching measured from Alternating Gradient Magnetometer (AGM) and is much smaller than that of the top Py from MOKE; the coercivity of the top Py from MOKE is closer to that of the second switching from AGM. These show that the non-collinearity provided by the two soft layers is not symmetric in reality even with a symmetric structure. The experimental observations might be due to the difference in the growing environment between the bottom Py layer and the top Py layer. [Preview Abstract] |
Saturday, November 3, 2012 2:24PM - 2:36PM |
H4.00003: Redesign of an AC Magnetic Susceptometer for smaller samples Andres Vargas, Ryan Fukuda, Smitha Sunny, Pei-Chun Ho A new AC magnetic susceptometer that measures samples of the 10 mg range has been built to improve upon our previous model in design and materials. The AC magnetic susceptometer will be measuring the magnetic susceptibility of our samples. It is made up of a sample holder, a primary coil, and a secondary coil. A current is inputted to the primary coil which provides an applied AC magnetic field. The sample lies at the center of one of the solenoids of the secondary coil and becomes polarized due the applied magnetic field. The polarization will cause an induced voltage on the secondary coil which is directly proportional to the sample's magnetic susceptibility. The new AC magnetic susceptometer contains roughly 1.30 and 1.32 more windings than the previous primary and secondary coil respectively. The improvements of the new AC magnetic susceptometer will result in a smoother and more accurate data curve. We will be using our AC magnetic susceptometer to determine a compound's phase transition, which is given by a sharp change in the induced voltage at a critical temperature. We tested our new susceptometer using an 11 mg sample of Gd. The sharp change of Gd's magnetic susceptibility at the critical temperature qualitatively agrees with our previous AC magnetic susceptometer data. [Preview Abstract] |
Saturday, November 3, 2012 2:36PM - 2:48PM |
H4.00004: Differences in the Magnetic Susceptibility of UCu$_{3.95}$Ni$_{1.05}$ due to Grinding Carlos Sanchez, Carmen Quen, Edith Soto The effects on the magnetic susceptibility due to grinding a sample of Ucu$_{3.95}$Ni$_{1.05}$ are studied using the Vibrating Sample Magnetometry (VSM) technique. Peculiar differences between powder and ingot material are found in measurements of magnetic susceptibility as a function of temperature at a constant magnetic field of 500 Oe. The data shows a magnetic phase transition at around 150K, which appears to affect a polycrystalline ingot more than a powder sample. We suspect a relation between the observed effects and a second phase present in the system. We will discuss likely identities of the second phase including the possibility of extrinsic impurities. Some potential implications to interpreting powder and ingot data will be addressed as well as ways to separate the second phase contribution from the total susceptibility. [Preview Abstract] |
Saturday, November 3, 2012 2:48PM - 3:00PM |
H4.00005: Real Space Rotational Spectroscopy: Measurement of the Rotational Excitation of a Single Molecule by the Scanning Tunneling Microscope Shaowei Li, Arthur Yu, Freddy Toledo, Zhumin Han, Wilson Ho The power of rotational transition spectra has long been demonstrated in the frequency domain by microwave spectroscopy, but its application in real space is limited. Using a scanning tunneling microscope (STM) and inelastic electron tunneling spectroscopy (IETS), we are able to conduct real-space measurements of rotational transitions of gaseous hydrogen molecules physisorbed on Au(110) surface. By varying the tip-substrate distance, we could precisely investigate how the environmental coupling modifies the structure of a single molecule with sub-Angstrom resolution. Rotational spectroscopy at the single molecule level provides a powerful tool for chemical identification as well as bond length measurement in both frequency and space domains. [Preview Abstract] |
Saturday, November 3, 2012 3:00PM - 3:12PM |
H4.00006: High Resolution Vibrational Spectroscopy at the Atomic Scale: CO on Au(110) and Cu(100), and C$_{2}$H$_{2}$ on Cu(100) Chen Xu, Chilun Jiang, Yanning Zhang, Ruqian Wu, Wilson Ho STM-IETS has been regarded as the ultimate tool to identify and characterize single molecules adsorbed on solid surfaces with atomic spatial resolution. With the improvement of the energy resolution obtained at $\sim$600 mK, STM-IETS is able to reveal subtle interactions between the molecule and its environment which was previously not possible at higher temperatures. Here we demonstrate the capability of sub-Kelvin STM on detecting the influence of the tip as well as the anisotropy of the reconstructed Au(110) surface on the low energy hindered vibrational motions of single adsorbed CO molecule. In the case of acetylene, more vibrational modes are resolved due to the enhanced spectral resolution. Single molecule vibrational spectroscopy with atomic scale spatial resolution opens new possibilities to probe molecular interactions with high spectral resolution. [Preview Abstract] |
Saturday, November 3, 2012 3:12PM - 3:24PM |
H4.00007: 3-dimensional indexation of the icosahedral diffraction pattern using the techniques of electron microscopy Antony Bourdillon The following facts about icosahedra need wider attention. 1) The golden section $\tau $ is as fundamental to the icosahedral structure (length /edge) as $\pi $ is to the sphere (circumference /diameter). 2) The diffraction series are in restricted Fibonacci order because the ratio of adjacent terms $f_{n}/f_{n-1}$ does not vary, but is the constant $\tau $. The series is therefore geometric. 3) Because of the tetragonal subgroup in the icosahedral point group symmetry, many axes in the icosahedral structure have identical orientation to axes in the face centered cubic matrix of Al$_{6}$Mn [1] (e.g. [100] and [111]). On these bases, a three dimensional stereographic projection will be presented. 4) A quasi-Bragg law is derived that correctly represents the diffraction series in powers of $\tau$ [2]. Furthermore, by employing the normal conventions of electron microscopy, all diffraction patterns are completely indexed in three dimensions. These are the topic of this presentation. Significant consequences will be presented elsewhere: 1) The diffraction pattern intensities near all main axes are correctly simulated, and all atoms are located on a specimen image. 2) The quasi-Bragg law has a special metric. Atomic locations are consistently calculated for the first time. 3) Whereas the Bragg law transforms a crystal lattice in real space into a reciprocal lattice in diffraction space, the quasi-Bragg law transforms a geometric diffraction pattern into a hierarchic structure. 4) Hyperspatial indexation [3] is superceded. [1] Shechtman, D.; Blech, I.; Gratias, D.; Cahn, J.W., Metallic phase with long-range orientational order and no translational symmetry, Phys. Rev. Lett., \textbf{1984}, 53, 1951-3. [2] Bourdillon, A. J., Nearly free electron band structures in a logarithmically periodic solid, Sol. State Comm. \textbf{2009}, 149, 1221-1225. [3] Duneau, M., and Katz, A., \textit{Phys Rev Lett} \textbf{54}, 2688-2691 [Preview Abstract] |
Saturday, November 3, 2012 3:24PM - 3:36PM |
H4.00008: Exact Diagonalization studies of Entanglement Entropy of zig-zag spin chains with Heisenberg and ring-exchange interaction Jon Spalding, Dong-Ning Sheng In the study of interacting quantum spin chains, the ground state wavefunction carries information about the phases of matter that occur for different interaction parameters. In this case, a spin-1/2 chain with 3 interaction terms in the Hamiltonian--nearest neighbor, next nearest neighbor, and ring exchange, is investigated using entanglement entropy to map out a ground state phase diagram. In addition, further information can be obtained from the entanglement spectrum. Finally, preliminary investigations of the effects of an impurity on this triangular Heisenberg ladder are reported. [Preview Abstract] |
Saturday, November 3, 2012 3:36PM - 3:48PM |
H4.00009: Experimental investigation of the temperature effects on CO$_{2}$ permeability of fractured coal rock Yang Ju, Huijie Wang, Ranjith Pathegama Gamage, Huafei Sun Accurate prediction of gas permeability is of great significance for coalbed methane production and CO$_{2}$ sequestration. The permeability of coal rock plays a key role in determining coalbed methane productivity in the application of simultaneous excavation of coal and gas in deep coal mines. The main objective of this study is to investigate the temperature effects on the permeability of fractured coal rock in deep coal seams. The CO$_{2}$ permeability of the fractured coal samples obtained from Ping Ding Shan coalfield, China, was measured using high pressure undrained triaxial apparatus. To probe the temperature effects, four levels of temperatures (25-75${^\circ})$ were tested with the injection pressures ranging from 7 to 11MPa and a confining pressure of 15MPa. It is shown that the CO$_{2}$ permeability of the fractured coal rock rises apparently with an increasing temperature. The physical mechanism that governs the CO2 permeability of coal rock is discussed in this study. [Preview Abstract] |
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