Bulletin of the American Physical Society
85th Annual Meeting of the APS Southeastern Section
Volume 63, Number 19
Thursday–Saturday, November 8–10, 2018; Holiday Inn at World’s Fair Park, Knoxville, Tennessee
Session G03: Neutron Science at ORNL |
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Chair: Ward Plummer, Louisiana State University Room: Holiday Inn Knoxville Downtown LeConte |
Friday, November 9, 2018 2:00PM - 2:30PM |
G03.00001: Inelastic Neutron Scattering: A Powerful Probe of Condensed Matter Invited Speaker: Nancy L Ross Inelastic neutron scattering (INS) is a powerful tool to probe the dynamic and static properties of condensed matter at the atomic scale. As neutrons are sensitive to hydrogen, they provide key information about the structure and dynamics of the water species in materials. Neutrons have a magnetic moment, so neutron studies reveal information about the magnetic properties of materials. Neutrons can also be used as a probe of molecular vibrations. INS determines the full lattice vibrational spectrum from which the thermodynamic driving forces, including entropic factors, can be determined. It is therefore a complementary method to infrared and Raman spectroscopy and has the advantage over these techniques as it is not subject to selection rules. In this presentation, examples that display each of these unique features of INS will be discussed. First, INS studies of water species confined to the surfaces of metal-oxide surfaces of nanoparticles are given and shown how this affects their stabilities. Second, novel magnetic spin transitions observed at low energies in metal-oxide nanoparticles are discussed. Third, INS spectra for a set of zeolitic imidazolate framework (ZIF) polymorphs synthesized by mechanochemistry are presented. The low-frequency vibrations observed in the INS spectra control the thermodynamic stabilities of the polymorphs and are correlated with physical phenomena such as gate-opening and / or shear-induced phase transitions that signify the onset of structural instability. The results from these studies have immense broader impact as they contribute to our fundamental knowledge of condensed matter by relating structures with their lattice dynamics, energetics and entropies. |
Friday, November 9, 2018 2:30PM - 3:00PM |
G03.00002: Opportunities in Quantum Materials Research using Neutron Scateering Invited Speaker: Clarina R dela Cruz Quantum materials will arguably be the key materials to push forward the forefront energy relevant technologies of the future. Having two powerful neutron sources at the Oak Ridge National Laboratory, enables us to be positioned strongly to use neutron scattering in unveiling the structure of, and dynamics in quantum systems that lead to fundamental understanding and control of quantum phenomena such as coherence, entanglement and novel emergent states. quantum critical phenomena among others, with a range of correlation strength in them. With the increasing progress in instrumentation, the instruments at ORNL are able to study systems in extreme environments of ultra-low temperatures, high magnetic field as well as high pressure. In this talk, I will give several examples of quantum materials problems where neutron scattering played a crucial role with some prospects for possible studies in unconventional quasi one dimensional superconductors, quantum spin liquid systems and multiferroic materials. |
Friday, November 9, 2018 3:00PM - 3:30PM |
G03.00003: Exotic magnetic matter and the search for spin-liquids Invited Speaker: Martin P Mourigal Magnetism is a fascinating phenomenon: it is rooted in relativistic quantum mechanics and yet an integral component of the technologies we use every day. In magnetic insulators, where atomic-scale magnetic dipoles carried by electrons are closely bound to a crystal lattice, novel phases of matter with no classical analogues are possible. Chief among these phases are spin-liquids, in which strong fluctuations of magnetic dipoles (spins) preclude conventional magnetic order even for temperatures low compared to the average interaction between spins. Such exotic magnetic matter is of great fundamental interest because it features a wealth of coherence and entanglement phenomena – the hallmarks of the quantum world – and is often amenable to theoretical and computational predictions. In this talk, I will present experimental research that brings together materials chemistry, neutron scattering and computer modeling to search for spin-liquids in a range of compounds with one-dimensional, triangular and kagome lattice structures. My talk will emphasize the importance of neutron scattering instrumentation at large-scale facilities to probe complex materials behavior in which chemical disorder, geometrical frustration and quantum fluctuations interplay to stabilize – or destroy – spin-liquid physics.
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Friday, November 9, 2018 3:30PM - 4:00PM |
G03.00004: Elastic and electronic tuning of magnetoresistance in MoTe2 Invited Speaker: Despina A Louca Quasi-two dimensional transition metal dichalcogenides (TMD) exhibit dramatic properties that may transform electronic and photonic devices. We report on how the anomalously large magnetoresistance (MR) observed under high magnetic field in MoTe2, a type II Weyl semimetal, can be reversibly controlled under tensile strain. The MR is enhanced by as much as ∼30 % at low temperatures and high magnetic fields, when uniaxial strain is applied along the a-crystallographic direction and reduced by about the same amount when strain is applied along the b-direction. We show that the large in-plane electric anisotropy is coupled with the structural transition from the 1T' monoclinic to the Tdorthorhombic Weyl phase. Controlled switching across the Td- 1T' phase boundary is achieved by minimal tensile strain. The sensitivity of the MR to tensile strain could have its origin to the nontrivial spin-orbital texture of the electron and hole pockets in the vicinity of Weyl points. Our ab initio calculations indeed show a significant orbital mixing on the Fermi surface, which is modified by the tensile strains. |
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