Bulletin of the American Physical Society
Far West Section Fall 2022 Meeting
Volume 67, Number 10
Friday–Saturday, October 7–8, 2022; University of Hawaiʻi at Mānoa, Honolulu, HI
Session G01: Condensed Matter |
Hide Abstracts |
Chair: Jake Koralek, SLAC National Accelerator Laboratory Room: University of Hawai'i at Manoa, East-West Center Keoni |
Friday, October 7, 2022 1:45PM - 1:57PM |
G01.00001: Shape-induced pairing of active colloids propelled by induced-charged electrophoresis William E Uspal, Ruben Poehnl Metallo-dielectric Janus particles can self-propel in liquid solution when exposed to AC electric fields via induced charge electrophoresis (ICEP). In recent experiments conducted in the Snezhko group, it was observed that ICEP Janus particles with discoidal shape can spontaneously form stationary bound pairs separated by a liquid-filled gap. Paired particles exhibit “head-on” alignment, i.e., the particles’ axes of symmetry are aligned with the center-to-center vector, and the gap width decreases with increasing frequency of the AC field. Strikingly, this pairing is not observed for spherical particles. In order to rationalize these observations, we develop a theoretical model for collisions between two ICEP particles interacting via self-induced hydrodynamic and electric fields. We recover the experimental observations, finding that hydrodynamic interactions dominate the pairing; effectively, the particles behave as field-tunable “squirmers.” In particular, we show that “head-on” alignment is driven by a coupling between the oblate shape of the particles and hydrodynamic flows generated by swimming activity. In the framework of our model, we explore general implications for shape-induced pairing of active colloids. Our findings suggest that self-organization of ICEP particles could be “programmed” via particle shape and surface patterning. |
Friday, October 7, 2022 1:57PM - 2:09PM |
G01.00002: Investigating the structural evolution of warm dense aluminum using single-shot mega-electron-volt ultrafast electron diffraction Benjamin K Ofori-Okai, Adrien Descamps, Zhijiang Chen, Luke Fletcher, Emma E McBride, Mianzhen Mo, Mianzhen Mo, Xieyu Na, Xiaozhe Shen, Jie Yang, Xijie Wang, Siegfried H Glenzer Warm Dense Matter (WDM) refers a regime where materials possess a simultaneously high density (ρ ~ 1 g/cm3) and temperature (T ~ 1 eV = 11605 K). Intense lasers pulses can drive thin metal foils to WDM conditions. Initially, the laser pulse heats the electrons, and subsequent equilibration between the electrons and the solid lattice yields a state of high temperature and density. While this method has been used to produce and study WDM, it has only recently been possible to study the structural evolution of this complex state of matter. |
Friday, October 7, 2022 2:09PM - 2:21PM |
G01.00003: Surface Morphology of Thermally Annealed Copper Phthalocyanine Thin Films Ryan T Mizukami, Thomas Gredig The effects of thermal annealing on post-deposition Copper Phthalocyanine (CuPc) thin films are systematically studied. Several CuPc thin films are concurrently deposited at room temperature and separately annealed in vacuum at temperatures up to 320°C for 30 minutes. Atomic force microscopy images show that the surface morphology changes from small round crystals around 59 nm in diameter to elongated crystals randomly oriented on the surface as the annealing temperature rises. This work demonstrates how the post-annealing procedure can affect structural properties in small molecular thin films. |
Friday, October 7, 2022 2:21PM - 2:33PM |
G01.00004: 19F-NMR and magnetic susceptibility in the normal state of LaO0.5F0.5BiS2 superconductor Oscar O Bernal, Shrishti Yadav, Silverio Delgado, Douglas E MacLaughlin, Lei Shu, Kevin Huang We report 19F-NMR spectral parameters together with complementary magnetic susceptibility measurements in an ambient-pressure-annealed powder of LaO0.5F0.5BiS2; Tc ~3K. NMR measurements and bulk magnetization experiments were performed as functions of temperature T and applied magnetic field H. The 19F-NMR linewidth grows slowly with decreasing temperature from room temperature to about T*~10 K. Below T*, the linewidth increase is anomalous and consistent with the appearance of superconducting regions in the sample. The lineshift, measured with respect to CaF2, is T-independent above T* and decreases noticeably with decreasing T below it. Although the linewidth above T* can be attributed to random paramagnetic impurities, the lineshift cannot be understood in terms of impurity magnetization effects. Instead, the line position is seen to be dominated by the chemical shift and by the direct-contact interaction of 19F with a relatively low density of conduction electrons. The decrease in lineshift below T* together with the lineshape symmetry suggest that the effect is happening throughout the sample and not just in some regions. T~10 K is the maximum Tc this material displays under pressure, or when samples of it are pressure annealed. We conjecture that we are seeing either a lack of superconducting coherence or the effects of pair-breaking fluctuations; either or both being caused by the presence of strong paramagnetic impurities in the starting materials. |
Friday, October 7, 2022 2:33PM - 2:45PM |
G01.00005: Vibrational Characterization of Spatial Inhomogeneity of Single Surface-Adsorbed DMP Isocyanide Molecules Liya Bi, Liya Bi, Amanda Chen, Krista Balto, Joshua Figueroa, Tod A Pascal, Shaowei Li We studied the site-dependent adsorption geometries and vibrational fingerprints of the 2,6- Dimesitylphenyl (DMP) isocyanide molecules on Au(111) with scanning tunneling microscopy (STM) and inelastic electron tunneling spectroscopy (IETS) at 5 K. The STM topographic images reveal that the DMP isocyanides preferably bind to the surface sites with a relatively large curvature, such as the herringbone elbow sites and the step edges. IETS measurement shows a series of molecular vibrational features which demonstrate obvious spatial inhomogeneity among molecules adsorbed at different sites. It was found that certain vibrational modes exhibit energy shifts upon altering the electric field between the tip and molecules, which was tentatively assigned to first-order perturbation to the Hamiltonian by coupling to the molecular dipole or the Stark effect. Furthermore, the varying energy shifts of the same vibrational modes at different sites could indicate a spatial variation of the molecular dipole moments due to different adsorption geometries. |
Friday, October 7, 2022 2:45PM - 2:57PM |
G01.00006: Study of the molecular arrangement of a CuPc/graphene/h-BN heterostructure Jacob D Weber, Francisco Ramirez, Ryan T Mizukami, Patrick T Barfield, Maya H Martinez, Thomas Gredig, Claudia Ojeda-Aristizabal We study the arrangement of a thin film of planar magnetic molecules of copper-phthalocyanine (CuPc) on a graphene/hexagonal Boron nitride (h-BN) heterostructure. Atomic Force Microscopy (AFM) reveals a dissimilar arrangement of the molecules on graphene with respect to its insulating counterpart h-BN, giving evidence of the importance of the interaction between π orbitals from graphene and the Cu-Pc molecules. Our surface characterization informs electronic transport measurements performed on CuPc/graphene/h-BN heterostructures. |
Friday, October 7, 2022 2:57PM - 3:09PM |
G01.00007: Twisted Graphene Heterostructures Michael Marcos Santos, Hui Cai
|
Friday, October 7, 2022 3:09PM - 3:21PM |
G01.00008: Characterizing Gate Defined Quantum Dots In A Mesa-Etched Silicon Nanowire Ashley N Corey
|
Friday, October 7, 2022 3:21PM - 3:33PM |
G01.00009: Geometrical Probes for Conductivity in the Hubbard Model Sobhan Sayadpour, Ettore Vitali
|
Friday, October 7, 2022 3:33PM - 3:45PM |
G01.00010: Thermal expansion of clathrate-II Na24Si136 Christian K Posadas, Winnie Wong-Ng, Mingjian Zhang, Yu-Sheng Chen, Antti J Karttunen, George S Nolas, Matt K Beekman Thermal expansion of the intermetallic clathrate Na24Si136 has been investigated using temperature dependent X-ray diffraction and first-principles calculations. Direct comparison of the thermal expansion of Na24Si136 with the low-density elemental modification Si136 provides insight into the effects of filling the silicon clathrate framework cages. The room-temperature linear coefficient of thermal expansion (CTE) is nearly a factor of 3 greater for Na24Si136 compared to Si136, indicating the guest atoms increase the anharmonicity of the interatomic interactions. Negative thermal expansion (NTE), observed in Si136 below 100 K, is absent in Na24Si136. In contrast to Si136, the thermal expansion behavior in Na24Si136 is relatively well described by the conventional Grüneisen-Debye model in the temperature range of 10–700 K. First-principles calculations in the quasiharmonic approximation correctly predict an increase in high-temperature CTE with Na loading, although the increase is less than observed in experiment. The calculations also fail to capture the absence of NTE in Na24Si136, perhaps due to anharmonic effects and/or inadequateness of the ordered structural model used in the calculations. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700