Bulletin of the American Physical Society
2017 Annual Meeting of the Far West Section
Friday–Saturday, November 3–4, 2017; Merced, California
Session B2: Condensed Matter Physics |
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Chair: Hendrik Ohldag, SLAC National Accelerator Laboratory Room: COB2 263 |
Friday, November 3, 2017 2:00PM - 2:12PM |
B2.00001: Surface energy stabilization of cubic crystal phase in organic-inorganic Perovskite quantum dots at low temperatures. Som Sarang, Sara Bonabi, Parveen Kumar, Vincent Tung, Michael Scheibner, Jin Z. Zhang, Sayantani Ghosh Surface energy manipulations have led to modification of the crystal phase diagram of a nanoparticle, leading to unusual physical properties at low temperatures. In this work, we use low temperature photoluminescence (PL) as a framework to study phase transitions in CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbBr$_{\mathrm{3}}$ Perovskite quantum dots (PQDs) ligated with Octylaminebromide and 3-aminopropyl triethoxysilane At low temperatures (\textless 140 K), P-OABr undergoes phase transition from tetragonal to orthorhombic phase as seen from the emergence of a higher energy band (\textasciitilde 2.64eV) in the PL spectrum, while no phase transition is observed in P-APTES even at temperatures as low as 20 K. The absence of phase transition results from differences in surface energy stabilization, a prominent factor in quantum dots due to their nanoscale morphology and surface ligation. Using time resolved PL, at room temperature we observe a bi-exponential exciton recombination in P-OABr and P-APTES with average lifetimes of 3.5 ns and 6.9 ns respectively, while at temperatures \textless 140 K, the emerging high energy orthorhombic band has a lower recombination lifetime of the order \textasciitilde 300 ps. Our findings bring in new aspects of PQD phase stabilization linked to nanoscale morphology and surface energy manipulation [Preview Abstract] |
Friday, November 3, 2017 2:12PM - 2:24PM |
B2.00002: Phonon-induced polarization rotation in coupled quantum dots Andrew Jacobs, Joshua Casara, Cameron Jennings, Parveen Kumar, Michael Scheibner Coupled quantum dots have demonstrated the ability to promote coherent phonon behavior [1]. Such an effect is due to Fano-like quantum interference between continuum single-dot polaron and discrete spatially-indirect exciton states. This coherent phonon behavior manifests in the form of a nonlinear optical transparency [1], a phenomenon of interest for generating slow light [2] and other optical responses. Here, we consider spin---phonon correlation arising from optical selection rules and the optical nonlinearity of the Fano interference. The degree of polarization rotation is calculated using the difference in refractive index between Fano-like asymmetry and a conventional Lorentzian optical response. Under ideal conditions, we find that a single pair of coupled quantum dots, with spatial extent 10 nm, can lead to rotations of nearly 200 microradians. We also demonstrate the robustness of this rotation effect to lifetime of the indirect exciton, random charge fluctuations in the environment of the coupled quantum dots, and to the Fano asymmetry factor. We identify a ``sweet spot'' of spectral asymmetry that optimizes the amount of polarization rotation. Coherent phonon behavior is of interest for basic solid-state physics, and presents an opportunity to investigate its use for future phononic devices. [1] M. L. Kerfoot et al., Nat. Commun. \textbf{5}, 3299 (2014). [2] A. R. Jacobs et al., ``Optical response of coupled quantum dots to phonon coherence'' (in preparation). [Preview Abstract] |
Friday, November 3, 2017 2:24PM - 2:36PM |
B2.00003: Using InAs Quantum Dots for Quantum Sensing of Mechanical Motion Joshua Casara, Samuel Carter, Allan Bracker, Mijin Kim, Chul Soo Kim, Maxim Zalalutdinov, Brennan Pursley, Sophia Economou, Cyprian Czarnocki, Dan Gammon, Michael Scheibner Quantum sensing has proven to be one of the most precise tools ever devised. Consequently, the ability to couple quantum systems to mechanical motion is a promising avenue of research. We study a system consisting of an InAs quantum dot embedded in a mechanical resonator to better understand the effects of mechanical motion on a nanoscale system. Mechanical oscillations of the resonator induce large shifts in the optical transition energies, and influence the spin states of the quantum dot charge carriers. The ability to couple such spin states to mechanical motion is therefore favorable to high-precision sensing, and an interesting demonstration of interaction between the quantum and classical regimes. [Preview Abstract] |
Friday, November 3, 2017 2:36PM - 2:48PM |
B2.00004: Adjusting the synergistic performance of semiconducting and magnetic nanoparticle co-assemblies Mark Bartolo, Randy Espinoza, Jussi Amaral, Sayantani Ghosh A much sought after goal of nanosynthesis is creating artificial materials from self-assembled nano-constituents that would exhibit multifunctionality and \textit{in situ} responsiveness to external stimuli. We are investigating the ensemble behavior of Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$ magnetic nanoparticles (MNPs) and CdSe/ZnS quantum dots (QDs) when dispersed in electro-optically active liquid crystalline (LC) matrix. Prior research has demonstrated an enhancement in the QD emission with a small applied magnetic field, a result of synergistic interactions between nanoparticles. Here, we vary the sizes and relative proportions of QDs and MNPs in the assemblies. We aim to determine the limits of sensitivity of the enhanced brightening effect as a function of concentration of MNPs. Using scanning confocal photoluminescence microscopy, we observe that 20 nm MNPs co-assembled with 6 nm QDs exhibit the brightening effect at a dilute limit of 1:100 for MNP:QD, while decreasing the MNP sizes require higher proportions of the latter. Transmission electron microscopy (TEM) provided a structural image of the assemblies. This may be a potential platform for developing high sensitivity, small footprint, and low power magnetic field detectors. [Preview Abstract] |
Friday, November 3, 2017 2:48PM - 3:00PM |
B2.00005: Particle Hole Symmetry Breaking In the Fractional Quantum Hall Effect at $\nu = \frac{5}{2}$ William D. Hutzel, John J. McCord, Ben Stern, P. Raum, Hao Wang, V. W. Scarola, Michael R. Peterson The fractional quantum Hall effect (FQHE) is widely studied because of its exotic topological phases. The FQHE at $\nu = \frac{5}{2}$ is interesting because it supports excitations of non-abelian quasiparticles. These non-abelian particles are one possible candidate for use as qubits in topological quantum computations. The leading theoretical description of the FQHE at $\nu = \frac{5}{2}$ is the Moore-Reed Pfaffian and its particle hole conjugate the anti-Pfaffian. The Pfaffian and the anti-Pfaffian are the exact ground states of a three body Hamiltonian ($H_3$) and its particle hole conjugate ($H^\prime_3$), respectively. The Pfaffian breaks particle hole symmetry (PHS) explicitly while the physical interaction (Coulomb) is largely PHS. We define a PHS Hamiltonian (H$_2$) and ask is PHS breaking necessary in order to produce a Pfaffian ground state? To answer, we study $H(\alpha)= (1-\alpha)H_3 + \alpha H_2$ and tune alpha from 0 to 1. We show that the ground and low energy states for $H_2$ and $H_3$ remain adiabatically connected. This adiabatic connection shows the low energy states for $H_2$ and $H_3$ are in the same universality class. [Preview Abstract] |
Friday, November 3, 2017 3:00PM - 3:12PM |
B2.00006: Dispersion dynamics in HiTc Antony Bourdillon The key to understanding HiTc is the Chemical hole [1] that replaces the isotope effect and lattice distortions of LoTc. Hall coefficients are positive in the former superconductor and negative in the latter. Since the Lorentz force can influence neither voids nor immobile ions, how do HiTc materials show positive Hall coefficients? Moreover, in the superconducting state, where \textbf{\textit{E}}$=$0, how is charge transported without resistance? Clear answers are given in dispersion dynamics [1] based on the stable wave packet. [1] \textit{High temperature superconductors -- science and processing}, Bourdillon A and Tan-Bourdillon NX, 1993, Academic. [2] \textit{Dispersion dynamics in the Hall effect and pair bonds in HiTc}, Bourdillon AJ, 2017, Nova Science. [Preview Abstract] |
Friday, November 3, 2017 3:12PM - 3:24PM |
B2.00007: Analysis of the temperature-dependent specific heat of Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ Shoji Hishida, Jesus Velasquez, Taylor McCullough-Hunter, Pei-Chun Ho, Brian Maple, Tatsuya Yanagisawa The compounds PrOs$_4$Sb$_{12}$ and NdOs$_4$Sb$_{12}$ have attracted interest due to their properties at low temperatures, where they exhibit unconventional heavy-fermion superconductivity and ferromagnetism respectively. The series of compounds Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ is being studied in order to understand the interaction between these effects. Previous studies have shown that there is competition between the superconducting and ferromagnetic effects and that for particular concentrations of Nd and Pr, the two phenomena coexist within the sample. In order to understand this system, the specific heat was measured in the normal state from 10 – 300 K. Thermodynamic parameters were extracted from the specific heat data for each sample, including the Debye Temperature, Einstein Temperature, and electronic specific heat coefficient. These provide information about the properties of the lattice and conduction electrons. The Einstein and Debye temperatures were both found to have a minimum around $x = 0.55$, which suggests a form of lattice-softening taking place at the Nd concentration where the superconductivity disappears and a possible quantum critical point may occur. [Preview Abstract] |
Friday, November 3, 2017 3:24PM - 3:36PM |
B2.00008: Pair Correlations in a Clean Magnetic Josephson Junction Alberto Garcia, Luis Leal, Andreas Bill We study pair correlations in superconducting-magnetic proximity systems made of inhomogeneous nanoscale magnetic films sandwiched between two superconductors. In the ballistic regime, we solve the Bogoliubov-de Gennes equations for a tight binding Hamiltonian and calculate the Gor'kov functions of the system. The goal is to determine how different parameters of the model affect the generation and relative weight of all four pair correlation symmetry states (singlet, triplets). We also compare the generation of correlations in the clean and the diffusive regimes. Different magnetic configurations are considered to this effect. [Preview Abstract] |
Friday, November 3, 2017 3:36PM - 3:48PM |
B2.00009: Praeseodymium -123: 30 Years Later\textellipsis Why Isn't It Superconducting\textellipsis or Even Conducting? Maria Lopez-Morales, Paul Grant The years 1986-87 witnessed the explosion of the discovery of the rare earth copper oxide perovskite family of high temperature superconductors. Alone of those with the single phase RE-123 stoichiometry that remained non-superconducting\textellipsis or even conducting \textellipsis at all temperatures down to 0.4 K was Pr-123.$^{\mathrm{1}}$ Today, this finding remains one of the principal mysteries of the HTSC family of compounds. We revisit this continuing conundrum from the perspective of today, 30 years later, and explore various quantum models which might clarify this issue, as well as propose possible applications of Pr-123 films to embody Landauer-Buttiger ballistic-controlled ``smart'' gates in future MOSFET devices.$^{\mathrm{2\thinspace }}$ \newline $^{\mathrm{1}}$ M.E. Lopez-Morales, et al., Physical Review B 41, 6655 (1990). \underline {http://w2agz.com/Publications/Science{\%}20{\&}{\%}20Technology/IBM/72{\%}20(1990){\%}20Role{\%}20of{\%}20Oxygen{\%}20in{\%}20PrBa\textunderscore 2Cu\textunderscore 3O\textunderscore 7-y{\%}20-{\%}20Effect{\%}20on{\%}20Structural{\%}20and{\%}20Physical{\%}20Properties.pdf} \newline $^{\mathrm{2}}$ P.M. Grant, Possible Quantum Transport in Pr-123 Perovskites, 2012 Meeting of the Cal-Nev Section of the APS. \underline {http://w2agz.com/Presentations/2012/11-02{\%}20Cal-Nev-APS{\%}20San{\%}20Luis{\%}20Obispo/Cal\textunderscore Poly\textunderscore Talk-Static.pdf} [Preview Abstract] |
Friday, November 3, 2017 3:48PM - 4:00PM |
B2.00010: Were the Basic Physics Underlying High Temperature Superconductivity Revealed in 1941? Paul Grant It is now some three decades since the discovery of high temperature superconductivity by Bednorz and Mueller in 1986.$^{\mathrm{\thinspace 1}}$ Yet, despite the efforts of dozens of outstanding theoretical physicists and their parent institutions worldwide, and the expenditure of tens of millions of dollars in supporting grants, its detailed BCS pairing mechanism remains a mystery. It is generally believed, and experimentally driven, that some combination of lattice vibrations (phonons) and paramagnetic fluctuations (spinons) are at work. Perhaps a clue to such was revealed by Chauncey Starr in a Physical Review paper published in late 1941.$^{\mathrm{2}}$ Starr focused on then recent measurements of the paramagnetic susceptibility of several transition metal complexes (see references in$^{\mathrm{2}})$, using a model of a coupled spin-phonon dispersion to interpret the experimental results. In this talk, we propose revisiting this paper as a path to resolving the HTSC fermion-boson-fermion pairing enigma, and suggest a possible computational path to pursue. \newline $^{\mathrm{1}}$ J.G. Bednorz and K.A. Mueller, Z. Phys. B -- Condensed Matter 64, 189 (1986). \newline $^{\mathrm{2}}$ C. Starr, Phys. Rev. 60, 241 (1941). \newline [Preview Abstract] |
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