Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A44: Crystalline Structure and Electronic Correlations |
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Sponsoring Units: DCMP Chair: Jason Hancock, Univ of Connecticut - Storrs Room: LACC 504 |
Monday, March 5, 2018 8:00AM - 8:12AM |
A44.00001: Abstract Withdrawn
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Monday, March 5, 2018 8:12AM - 8:24AM |
A44.00002: Time-Resolved Optical Study Of The Ferroelectric Metal LiOsO3 Nicholas Laurita, Alon Ron, Youguo Shi, David Hsieh Recently, an inversion symmetry breaking metal-to-metal phase transition (Tc = 140K) was shown to exist in the strongly correlated spin-orbit coupled metal LiOsO3, potentially realizing the long sought after ferroelectric metal first proposed by Anderson and Blount over a half century ago. However, the microscopic origin of the ferroelectric-like distortion below Tc remains unclear. In this work, ultrafast optical pump-probe spectroscopy experiments are utilized to address this question. We �find the fast carrier dynamics to display obvious signatures of the transition, with differing temperature dependence above and below Tc. A two-temperature model is developed to extract the electron-phonon coupling constant of LiOsO3, which is found to be larger than previously thought. Our results provide critical insight into the dynamics of this uncommon phase transition. |
Monday, March 5, 2018 8:24AM - 8:36AM |
A44.00003: Signatures of an order-disorder transition in LiOsO3 from second harmonic optical anisotropy Jun-Yi Shan, Alberto De la Torre, Liuyan Zhao, Cameron Dashwood, Youguo Shi, David Hsieh Metallic LiOsO3 undergoes an unusual ferroelectric-like structural phase transition below Tc = 140 K that is believed to realize the first example of the long-sought Anderson-Blount ferroelectric metal. However, the microscopic origin of this phase transition remains unsettled. In this talk I will present optical second harmonic generation rotation anisotropy measurements on LiOsO3 single crystals to probe the presence of both static and dynamic inversion symmetry breaking. Our results reveal a strong order-disorder character to the phase transition. |
Monday, March 5, 2018 8:36AM - 8:48AM |
A44.00004: Infrared(IR) study of strong negative thermal expansion(NTE) material Scandium trifluoride(ScF3) Sahan Handunkanda, Jason Hancock Strong, thermally persistent, isotropic NTE is a rare phenomenon that has been observed in ScF3.We have previously reported unusual softening of an optical mode branch along the edges of the BZ and strong quasi-elastic peak appearance at low temperatures were observed in an IXS, providing copious evidence of a structural quantum phase transition near the ground state of this system[1]. |
Monday, March 5, 2018 8:48AM - 9:00AM |
A44.00005: Temperature dependence of the elastic moduli of ScF3 Boris Maiorov, Yongkang Luo, Marcel Remillieux, Jonathan Betts, Gian Guzman-Verri, Vladimir Voronov, Sahan Handunkanda, Connor Occhialini, Jason Hancock, Peter Littlewood, Albert Migliori Understanding Negative Thermal Expansion materials (NTE) is critical to develop materials with tunable volumetric changes as a function of temperature. ScF3 has attracted attention because of its simple chemical structure and the extended range where NTE is observed (up to 1100K). Measuring elastic moduli can bring light on the interatomic potentials being proposed to explain the NTE. |
Monday, March 5, 2018 9:00AM - 9:12AM |
A44.00006: Negative thermal expansion in thiospinel LiGaCr4S8 Ganesh Pokharel, Andrew Christianson, David Mandrus, Andrew May, Hasitha Suria Arachchige, Ashfia Huq, Georg Ehlers, Simon Kimber, Stuart Calder, Lekh Poudel The thiospinel LiGaCr4S8 has been synthesized using solid state synthesis. X-ray diffraction, neutron diffraction, magnetic susceptibility and heat capacity measurements were carried out to study the physical and magnetic properties. The crystal structure of LiGaCr4S8 is derived from the well-known spinel structure, AB2X4, where Li and Ga occupy alternating A sites. The inequivalent cation ordering in A-sites leads to a reduction in the symmetry and the development of a breathing pyrochlore lattice with an alternating array of larger and smaller Cr4 tetrahedra. Negative thermal expansion is observed between 111 and 11 K. No distortion from cubic symmetry was detected, however anomalies in the magnetic properties are observed corresponding to the region of negative thermal expansion. In particular, the magnetic susceptibility deviates from Curie-Weiss behavior coincident with the onset of negative thermal expansion. Whereas the recovery of normal thermal expansion is accompanied by the appearance of a broad peak in the magnetic susceptibility. Taken together, these results suggest strong magnetoelastic coupling in LiGaCr4S8. |
Monday, March 5, 2018 9:12AM - 9:24AM |
A44.00007: Study of Successive Dimensional Transition in (TMTTF)2PF6 by Synchrotron X-ray Diffraction Shunsuke Kitou, Naoyuki Katayama, Tadashi Kawamoto, Kunihisa Sugimoto, Toshikazu Nakamura, Hiroshi Sawa (TMTTF)2PF6 undergoes a multistep phase transition as the temperature decreases [1]. One of these transitions is called a “structure-less transition” [2,3], and these detailed structures were unknown for many years. With synchrotron X-ray diffraction, we observed a slight structural difference owing to effect of charge-order transition between two TMTTF molecules in a dimer, which corresponds to the charge transfer. The two-dimensional Wigner crystallization was determined from an electron density analysis using core differential Fourier synthesis (CDFS) method [4]. Furthermore, we found that the ground state due to tetramerization, called the spin-Peierls phase, is a three-dimensional transition with interchain correlation. |
Monday, March 5, 2018 9:24AM - 9:36AM |
A44.00008: Pressure and Temperature Dependent Raman Scattering of Sr2IrO4 and Sr2Ir1-xCoxO4 Kousik Samanta, Danilo Rigitano, Fabio Ardito, NARCIZO SOUZA NETO, Eduardo Granado Structural and lattice dynamical behavior of novel spin-orbit entangled 5d-Mott insulator Sr2IrO4 and Sr2Ir1-xCoxO4 have been investigated by pressure and temperature dependent Raman scattering. Anomalies in phonon intensities, energies, and line-widths of Sr2IrO4 were observed at 17, 30 and 40 GPa, with no detected structural phase transition up to 45 GPa. Our findings reveal a transition of Ir4+: 5d5 electrons from the Jeff = 1/2 configuration below 17 GPa to a competing disentangled state with a hole in a xz ± iyz orbital above 40 GPa, crossing a mixed disordered phase at intermediate pressure. A Fano-interference is also detected in pressure range between 17 to 40 GPa, revealing that the low-energy orbital dynamics of Ir4+ (5d5) electrons is impacted by the transitions. Temperature dependent (20 - 300K) Raman scattering of Sr2IrO4 and Sr2Ir1-xCoxO4 shows an anomalous softening (~7%) of A1g mode at 276 cm-1. This anomalous change could be due to the additional contribution of spin-phonon coupling along with anharmonicity. Fano-interference is detected in Sr2Ir1-xCoxO4 throughout the studied temperature range, however this phenomena is absent in Sr2IrO4, indicating the formation of an electronic continuum in Sr2IrO4 due to Co substitution. |
Monday, March 5, 2018 9:36AM - 9:48AM |
A44.00009: Rigidity and mechnisms in negative thermal expansion materials Connor Occhialini, Sahan Handunkanda, Erin Curry, Jason Hancock Negative thermal expansion (NTE), or a material's tendency to shrink when heated, is an unusual phenomenon which defies intuition. For the type of NTE driven by intrinsic fluctuations of the lattice, we attempt to put this phenomenon in context by exploring a 2D lattice model often cited in NTE papers which is based on rigid molecules flexibly linked where they join and possessing a single collective degree of freedom. We consider carefully the classical, quantum, and thermal consequences of this conceptually simple model and attempt to apply it to real materials to show the limits and benefits of the approach. |
Monday, March 5, 2018 9:48AM - 10:00AM |
A44.00010: Negative thermal expansion near two structural quantum phase transitions Connor Occhialini, Sahan Handunkanda, Ayman Said, Sudhir Trivedi, Gian Guzman-Verri, Jason Hancock We present an inelastic X-ray scattering study of the structural phase transitions and thermal expansion (TE) behavior of the mercurous halides (Hg2X2 with X=Br,I). The body-centered tetragonal (BCT) to orthorhombic transition at Tc = 150K in Hg2Br2 is induced by the freezing of the transverse acoustic phonon at the X-point in the BCT Brillouin zone, as we confirm by the soft-mode behavior and static structure factor. For the case X = I, the X mode does not freeze but softens considerably, extrapolating to Tc = -22K which implies that mercurous iodide at low temperatures is situated very close to a structural quantum phase transition (SQPT). While Hg2Br2 displays normal TE, we report for the first time that low temperature Hg2I2 reveals significant negative TE behavior on the approach to the SQPT below T = 70K. We contextualize this result against the 3d-transition metal trifluorides, in particular ScF3 which is another system that displays negative TE above an incipient structural transition. |
Monday, March 5, 2018 10:00AM - 10:12AM |
A44.00011: Advanced Synthesis and High Resolution Electron Microscopy Characterization of Nanomaterials Confined Inside Nanotubes
Thang Pham, Sehoon Oh, Patrick Stetz, Seita Onishi, Christian Kisielowski, Marvin Cohen, Alex Zettl Novel properties may arise when lowering the dimensionality of materials because of the quantum confinement effect and the reducing of neighbor atoms. In this talk I will present different approaches to grow nanomaterials (metal, metal oxides, chalcogens and metal chalcogenides) inside boron nitride and carbon nanotubes (NTs). The spatial confinement of NT’s cavity promotes and stabilizes the formation of nanostructures with new phases and geometries. The encapsulation of nanotube walls protects the core materials from the chemical oxidation with the environment, which has been shown to have detrimental effects on the structure integrity and physical properties of the nanomaterials. The encapsulated materials are very mobile and they rotate, twist and shuttle inside nanotube channels. The nanomaterials filled nanotube system resembles the nanoscaled test-tube, which enables various in-situ studies of nanomaterials growth and interactions.<div id="UMS_TOOLTIP" style="position: absolute; cursor: pointer; z-index: 2147483647; background-color: transparent; top: -100000px; left: -100000px; background-position: initial initial; background-repeat: initial initial;"> </div> |
Monday, March 5, 2018 10:12AM - 10:24AM |
A44.00012: Cryogenic Near-Field Microscopy and Spectroscopy of strongly-correlated materials at the Nanoscale Max Eisele, Adrian Cernescu, Tobias Gokus We will introduce the first commercially-available, cryogenic near-field optical microscope (cryo-neaSNOM) that is capable of performing optical microscopy and spectroscopy at cryogenic temperatures (<10K) with 10nanometer spatial resolution. The cryo-neaSNOM will enable unique and valuable insights into modern nano-structured materials in physical, chemical, and biological science. At cryogenic temperatures, this microscope has great potential to unravel the origin of peculiar quantum phenomena in strongly-correlated materials, e.g. superconductivity, charge-density-waves, or insulator-to-metal transitions. Since all these effects are extremely sensitive to their local, microscopic environment a detailed optical study of the materials at the nanoscale using near-field optical microscopy while simultaneously controlling the temperature will grant the cryo-neaSNOM a complete new access to understand the behavior of these material systems. In this presentation we will introduce the basic principles of near-field microscopy for imaging and spectroscopy with 10nanometer spatial resolution. In addition we demonstrate the extension of near-field microscopy to cryogenic temperatures with an overview on possible applications as well as first demonstrations. |
Monday, March 5, 2018 10:24AM - 10:36AM |
A44.00013: Linear Optical Conductivity and the Incoherent charge transport in BaCoS2 Ricardo Lobo The optical conductivity of BaCoS2 shows an unusual linear frequency dependence, over a broad spectral range, in contradiction with a Mott charge-transfer insulator scenario assumed for this material. A linear optical conductivity is generally explained by the presence of Dirac-cones in three dimensions. However, the Dirac cones in BaCoS2 are far from the Fermi level. An ab initio DMFT calculation, including a retarded Hubbard interaction, explains the data in terms of an incipient opening of a Co(3d)-S(3p) charge-transfer gap together with an incoherent charge transport driven by electronic correlations. We show that BaCoS2 does not follow a Fermi liquid scenario and has Hund's metal properties arising from an incipient Mott phase destabilized by strong low-energy charge fluctuations. |
Monday, March 5, 2018 10:36AM - 10:48AM |
A44.00014: Observation of a Quantum Dipole Liquid State in an Organic Quasi-Two-Dimensional Material Nora Hassan, William Cunningham, Martin Mourigal, Elena Zhilyaeva, Svetlana Torunova, Rimma Lyubovskaya, Natalia Drichko We demonstrated experimentally using inelastic (Raman) scattering technique that new charge degrees of freedom emerge in a molecule-based Mott insulator $\kappa$-(BEDT-TTF)$_{2}$Hg(SCN)$_{2}$Br resulting in quantum dipole liquid state. Electric dipoles localized on molecular dimer lattice sites do not order at low temperatures and fluctuate with frequency of about 40 $cm^{-1}$. Such fluctuations were detected by analyzing the line shape of charge-sensitive $\nu_2$ vibration of BEDT-TTF molecule, and by a direct observation of a collective mode related to dipole fluctuations at 40 $cm^{-1}$. The shape of $\nu_2$ vibrational band was modeled using the two-site jump model to calculate the fluctuation frequency. The low energy collective mode associated with those fluctuations shows temperature dependence that is in agreement with vibrational band behavior. The heat capacity shows a low-temperature linear term $\gamma\approx$ 13 mJ K$^{-2}$mole$^{-1}$. Heat capacity and Raman scattering response support a scenario where the composite spin and electric dipole degrees of freedom remain fluctuating down to the lowest temperatures. Such Fluctuations of electric dipoles coupled to S=1/2 spins on a triangular lattice of dimers have been suggested as a mechanism for spin-liquid behaviour. |
Monday, March 5, 2018 10:48AM - 11:00AM |
A44.00015: Thermodynamic signatures of the field-induced states of graphite David LeBoeuf, Willem Rischau, Gabriel Seyfarth, Robert Robert Kuechler, Martin Berben, Steffen Wiedmann, Wojciech Tabis, Medhi Frachet, Kamran Behnia, Benoit Fauque When a magnetic field confines the carriers of a Fermi sea to their lowest Landau level, electron-electron interactions are expected to play a significant role in determining the electronic ground state. Graphite is known to host a sequence of magnetic field-induced states driven by such interactions. Three decades after their discovery, thermodynamic signatures of these instabilities are still elusive. Here, we report the first detection of these transitions with sound velocity measurements. The evolution of elastic constant anomalies with temperature and magnetic field allows to draw a detailed phase diagram which shows that the ground state evolves in a sequence thermodynamic phase transitions. Our analysis indicates that the electron-electron interaction is not the sole driving force of these transitions and that lattice degrees of freedom play an important role. |
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