Bulletin of the American Physical Society
2011 Annual Meeting of the California-Nevada Section of the APS
Volume 56, Number 14
Friday–Saturday, November 11–12, 2011; Menlo Park, California
Session B3: Condensed Matter Physics I |
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Chair: Shirley Chiang, University of California, Davis Room: Bldg 51 - Kavli Auditorium |
Friday, November 11, 2011 1:30PM - 1:42PM |
B3.00001: Nuclear spin diffusion in quantum confined semiconductor nanostructures Daniel Henriksen, Ionel Tifrea We analyze the nuclear spin diffusion effect in semiconductor quantum wells in connection with dynamical nuclear polarization under optical pumping. The natural confinement provided by the particular geometry of quantum well structures is responsible for a position dependent nuclear spin relaxation time and a reduced nuclear spin diffusion. In particular, we consider the case of GaAs quantum wells within GaAlAs barriers and analyze the nuclear spin diffusion for As nuclei. Our results, obtained for different nuclear spin diffusion constants, show that nuclear spin diffusion has a relatively small effect on the overall polarization of As nuclei in these structures. [Preview Abstract] |
Friday, November 11, 2011 1:42PM - 1:54PM |
B3.00002: Transient-Grating Study of Electron and Hole Diffusion in (Ga,Mn)As Eric Kittlaus Dilute magnetic semiconductors are a class of materials exhibiting both semiconducting and ferromagnetic properties while being chemically similar to traditional semiconductors. This dual nature presents the opportunity for new ``spintronic'' devices, with the caveat that current dilute magnetic semiconductors are only ferromagnetic above their subzero Curie temperature, Tc. In order to develop new materials functional at room temperature, it is necessary to develop a better theoretical understanding of how such materials become magnetic, a result of microscopic electronic processes. One of the most common dilute magnetic semiconductors, (Ga,Mn)As, is produced by doping Gallium Arsenide with manganese. We use a laser-based experiment, transient-grating spectroscopy, to measure the diffusive motion of electrons and holes in (Ga,Mn)As, which provides information related to the processes which control magnetism in these materials. We present preliminary data and calculations and discuss further improvements in experimental design that will provide unprecedented insight into the microscopic workings of dilute magnetic semiconductors. [Preview Abstract] |
Friday, November 11, 2011 1:54PM - 2:06PM |
B3.00003: Spectral and polarization modulation of quantum dot emission in a one-dimensional liquid crystal photonic cavity Andrea L. Rodarte, C. Gray, L.S. Hirst, S. Ghosh We demonstrate spectral and polarization modulation of chemically synthesized core shell CdSe/ZnS quantum dots (QDs) embedded in a one-dimensional photonic cavity formed by a cholesteric liquid crystal (CLC) matrix. A Cano-wedge cell varies the pitch of the CLC leading to the formation of Grandjean steps. This spatially tunes the photonic stop band, changing the resonance condition and continuously altering both the emission wavelength and polarization state of the QD ensemble. Using high resolution spatially- and spectrally-resolved photoluminescence measurements we find that the emission is elliptically polarized and that the tilt of the ellipse, while dependent on the emission wavelength, additionally varies with distance across the Grandjean steps. This work opens up the possibility of designing new QD based optical devices, such as tunable single photon sources, where spatial control of wavelength and polarization of the embedded QDs would allow great flexibility and added functionalities. [Preview Abstract] |
Friday, November 11, 2011 2:06PM - 2:18PM |
B3.00004: Bulk Nuclear Magnetic Resonance of Topological Insulators D.M. Nisson, A.P. Dioguardi, J. Crocker, P. Klavins, N.J. Curro Topological insulators are materials that are insulating in the bulk but remain conducting on the surface. We present $^{209} $Bi nuclear magnetic resonance (NMR) spectra and relaxation rate data on single crystals of Bi$_{2}$Se$_{3}$ and Bi$_{2} $Te$_{2}$Se. Our preliminary data reveal significant differences in the local electric field gradient between these two materials, and indicate a large anisotropy in the spin- lattice and spin-spin relaxation rates. [Preview Abstract] |
Friday, November 11, 2011 2:18PM - 2:30PM |
B3.00005: Nuclear Magnetic Resonance Study of Hidden Order in URu2Si2 Kent Shirer, Adam Dioguardi, John Crocker, Nicholas apRoberts-Warren, Abigail Shockley, Peter Klavins, Nicholas Curro URu2Si2 is a heavy fermion system that has challenged researchers for many years due to its transition into a hidden order (HO) state at 17.5K. We present new nuclear magnetic resonance (NMR) data near the HO phase transition. An analysis of the spin-lattice relaxation rate and comparisons with other current work, provide insight into understanding the hidden order phase. [Preview Abstract] |
Friday, November 11, 2011 2:30PM - 2:42PM |
B3.00006: NMR Studies of pseudogap and electronic inhomogeneity in BSCCO-2212 J. Crocker, A.P. Dioguardi, N. apRoberts-Warren, A.C. Shockley, H.-J Grafe, Z. Xu, J. Wen, G. Gu, N.J. Curro We present O-17 NMR measurements on a single crystal of overdoped BSCCO-2212. We measure the planar oxygen's Knight shift (K), electronic field gradient (EFG), and spin lattice relaxation rate (1/T1) along each principle axis. Our analysis shows that the temperature dependence can be explained by a suppression of the density of states in the pseudogap region. [Preview Abstract] |
Friday, November 11, 2011 2:42PM - 2:54PM |
B3.00007: Jacobi Elliptic Functions and their Application in Classical Mechanics, Superconductivity and Magnetism Thomas E. Baker, Ovidiu E. Icreverzi, Andreas Bill A differential equation involving a third or fourth degree polynomial may be rewritten in terms of one of three elliptic integrals. These integrals can be inverted to define the Jacobi Elliptic Functions. An application of these functions is to solve non-linear second order differential equations involving circular trigonometric functions sine and cosine. We present solutions of problems in three different areas of physics that have similar Langrangian and associated Euler-Lagrange equations: the bead on a hoop, the Usadel equation of a dirty superconductor and the magnetization twist in a single magnetic layer. We discuss what type of solutions are obtained for these problems and how they relate to each other. [Preview Abstract] |
Friday, November 11, 2011 2:54PM - 3:06PM |
B3.00008: Nanoscale Near-Field Spectroscopic Imaging of Four Way Gold Bowtie Nano Antenna Structures Brandon Hessler, Ralph Damato, Terrance Dunlap, James Schuck, Yohannes Abate Nanometer-scale four way gold bowtie nano antenna structures, or ``four-ties,'' are imaged using scattering-type scanning near-field optical microscopy (s-SNOM) in the mid infrared frequency region. Bowties allow the focusing, manipulation, and steering of light on the nanoscale by making use of an enhanced and confined field in the gap of the nano antenna. The near-field distribution of these four way gold bowtie nano antenna structures show geometric and wavelength dependence as manifested in the amplitude and phase near-field images. Experimental results have also shown strong dependence of the field distribution on the polarization of the incident light. [Preview Abstract] |
Friday, November 11, 2011 3:06PM - 3:18PM |
B3.00009: Testing of a First Order AC Magnetic Susceptometer Ryan Fukuda, Smitha Sunny, Pei-Chun Ho A first-order AC magnetic susceptometer has been constructed and tested to find the magnetic response of strongly correlated electron materials. The instrument works by using a primary coil to apply a small AC magnetic field of .104 Oe to a sample with a cylindrical coil space of length .635 cm and diameter .355 cm. A lock-in amplifier is used to monitor the induced voltage from a set of secondary coils. By coupling a temperature-controlled system with this instrument, the change in the magnetic signal with respect to temperature is measured. Monitoring the signal changes may indicate the temperature that causes the material to transition to either a ferromagnetic, anti-ferromagnetic, or superconducting state. A 122.47 mg Gd polycrystal was used to test our susceptometer. The data qualitatively agrees with the previous results of magnetization vs. temperature of Gd single crystals by Nigh et al. [1]: there is a steep increase in the pick-up signal at 300 K where Gd becomes ferromagnetic and a peak at 210 K [1]. This susceptometer will be used for our future investigation of magnetic properties of rare earth compounds and nanoparticles in the temperature range of 10 K to 300 K. \\[4pt] [1] H. E. Nigh, S. Legvold, and F. H. Spedding, Physical Review 132, 1092 (1963) [Preview Abstract] |
Friday, November 11, 2011 3:18PM - 3:30PM |
B3.00010: Magnetic Properties of La$_{0.7}$Sr$_{0.3}$Mn$_{1-x}$Ni$_x$O$_3$ Perovskites Ruben Medina, H. Blackstead, B.W. Benapfl, Thomas F. Creel, Jinbo B. Yang, Mehmet Kahveci, Jagat Lamsal, Satish K. Malik, S. Quezado, O.A. Pringle, William B. Yelon, William J. James Using a SQUID magnetometer, we have studied the magnetic properties of La$_{0.7}$Sr$_{0.3}$Mn$_{1-x}$Ni$_{x}$O$_{3}$ ($x=0.05$, 0.10, 0.20 and 0.30) perovskites. Both temperature dependent and field dependent magnetic measurements show that the Curie temperature decreases as a function of doping, ranging from 380K in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ to 300K in La$_{0.7}$Sr$_{0.3}$Mn$_{0.7}$Ni$_{0.3}$O$_{3}$. Both magnetic measurements and neutron-diffraction refinements indicate long-range magnetic ordering in samples at low temperature. Transition phases from paramagnetic to ferromagnetic to antiferromagnetic ordering in samples at room temperature. [Preview Abstract] |
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