Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D46: Undergraduate Research IIIUndergrad Friendly
|
Hide Abstracts |
Sponsoring Units: SPS Chair: Brad Conrad, AIP Room: Room 314 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D46.00001: Anisotropic Magnetoresistance (AMR) of Phase Separated (La0.4Pr0.6)0.67Ca0.33MnO3 thin films Haben Belai Anisotropic magnetoresistance (AMR) of magnetic materials is the dependence of electric resistance on the angle between the current through the material and an applied magnetic field. Exploring AMR in various materials can help us understand the underlying physical phenomena leading to their properties and how they may be used in devices such as solid-state magnetic memory. We studied the AMR of the hole-doped manganite (La0.4Pr0.6)0.67Ca0.33MnO3 (LPCMO) grown in thin film form on the substrate NdGaO3 which exerts anisotropic stress on the material. AMR in LPCMO is likely due to the resultant anisotropic strain due to lattice mismatch with the substrate but with additional contribution from the well-known phase co-existence between ferromagnetic metallic (FMM) and insulating phases. We have collected and analyzed AMR data of LPCMO at different temperatures and magnetic fields to distinguish the effects of anisotropicstrain and phase separation. Our results show that anisotropic strain is not a significant contributor to AMR in the metallic phase and that AMR increases with temperature across the metal-insulator transition temperature unlike in single phase manganites such as La0.67Ca0.33MnO3. Hence, phase separation plays a leading role in generating AMR in LPCMO. |
Monday, March 6, 2023 3:12PM - 3:24PM |
D46.00002: Exfoliation of large high-quality graphene coupled with physically informed automated identification Laura R Zichi, Tianci Liu, Elizabeth Drueke, Liuyan Zhao, Gongjun Xu First isolated in 2004 with a piece of scotch-tape, graphene monolayers display unique properties and promising technological potential in next generation electronics, optoelectronics, and energy storage. This simple yet effective mechanical exfoliation technique has been applied to analogous materials to discover more two-dimensional (2D) atomic crystals which demonstrate distinct physical properties from their bulk counterpart, opening the new era of materials research. However, the difficulty in fabricating large flakes of high purity and the impractical manual inspection of optical images to identify 2D flakes, hinders practical commercial applications and fundamental research of these thin materials. Furthermore, despite the advancements brought by coupling deep learning algorithms with optical microscopy for automated flake identification, their high computational complexities, large dataset requirements, and more importantly, opaque decision-making processes limit their accessibilities. Therefore, as an alternative we have developed physically informed, transparent tree-based machine learning (ML) algorithms for the automated identification of exfoliated 2D atomic crystals under different optical settings. We then couple these successful ML methods with mechanical exfoliation followed by vacuum annealing of graphene to promote scalable fabrication of large flakes. We evaluate the purity of the flakes with Raman and atomic force microscopy. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D46.00003: Shift Current Response in Twisted Multilayer Graphene Sihan Chen, Cyprian K Lewandowski, Swati Chaudhary, Gil Refael Twisted bilayer graphene (TBG) has shown to be an excellent material for photovoltaic applications in the terahertz range due to its nontrivial band topology of flat bands. In twisted multilayer graphene (TMG), we observe the presence of multiple flat bands hybridizing with each other through a self-generated displacement field. We investigate the role of these additional flat bands in TMG in enhancing the shift current response. Our numerical calculation indicates that the additional transitions among different flat bands and to the dispersive Dirac cone led to an overall enhancement of shift current response. A new peak in shift current conductivity occurs at a wide range of fillings at frequency determined by the mean energy of the two bands near K and K’ points. In addition, we explore the connection between charge inhomogeneity in the moiré unit cell and the magnitude of shift current response. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D46.00004: Magnetic Properties of Ferromagnetic Cobalt Grown in an Applied Magnetic Field Caeli L Benyacko, Steven Flynn, Jared C Lee, Fuyan Ma, Khalil A Abboud, Mark W Meisel, James J Hamlin Preparation of cobalt crystals from a melt requires temperatures above its Curie temperature, TC = 1394 K, meaning the nucleation and growth will occur in the paramagnetic state. In this work, a sulfur flux was used and the liquidus was shifted as low as 1150 K [1], thereby allowing crystal formation in the ferromagnetic phase. A magnetic field, Bsyn = 0, 3 T, or 9 T, was applied during synthesis, and the resulting polycrystalline samples were characterized with XRD and magnetometry, which provided magnetization data, M(5 K ≤ T ≤ 300 K, B = 10 mT) and M(T = 5 K or 300 K, −1 T ≤ B ≤ 7 T), with B oriented parallel and perpendicular to the growth axis which was along Bsyn. Overall, our data are consistent with magnetism reported for single crystals [2,3]. However, the remnant magnetization was found to increase with the magnitude of Bsyn, while trends in other magnetic properties, such as the maximum value of magnetization and the coercive field, were not as clearly established. Our results demonstrate using a sulfur flux allows for nucleation and growth of cobalt crystals below TC while preserving known magnetic properties. |
Monday, March 6, 2023 3:48PM - 4:00PM Author not Attending |
D46.00005: A model for magnetoresistance in thin films using local topographic characterization data Catherine Phillips, Nicholas Breznay Thin-film quantum materials often show electrical transport signatures - like linear magnetoresistance - that are attributed to novel phenomena. However, there can be many alternative explanations for these transport signatures, such as local inhomogeneity or disorder effects. Parish and Littlewood (Nature 426, 162 (2003)) and subsequent researchers studied one model for electrical transport in the presence of disorder that can also give rise to a linear magnetoresistance. Researchers often discuss this model as an alternative explanation for linear magnetoresistance, but typically do not generate quantitative predictions or assess its suitability using local materials characterization data. We have implemented and tested an extension of the Parish and Littlewood model that uses scanning probe height maps as a proxy for local conductance. Our approach predicts local voltage and current transport throughout a material, shows good agreement with scanning potentiometry studies of graphene, and can be used to quantitatively assess disorder-based explanations for linear magnetoresistance and related effects. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D46.00006: Structural and magnetic characterization of chiral magnetic oxides of MMoTeO6 (M=Mn, Co) family Brady Wilson, August C Meads, Chetan Dhital Chiral magnetic oxides are subjects of strong interest due to two reasons: (a) There is the possibility of formation of non-collinear spin texture due to interplay between Dzyalloshinskii-Moriya interaction and uniform exchange interaction; (b) multiferroic properties due to broken space inversion symmetry and insulating behavior. In other words, there is a possibility of formation of novel magnetic textures and their manipulation using an external electric field in chiral magnetic oxides. With such hypotheses, we are investigating the chiral magnetic oxides of the MMoTeO6 (M=Mn, Co) family. Our initial structural and magnetic characterization indicate the presence of non-collinear magnetic structure and magnetodielectric coupling in CoMoTeO6 and MnMoTeO6. I will present results of Raman scattering, dc magnetization, ac magnetic susceptibility, and dielectric measurements on MnMoTeO6 and CoMoTeO6. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D46.00007: Structural Phase Patterning of MoS2 Christopher A Barns, Scott A Dietrich, Arash Akbari-Sharbaf All modern electronics consist of three basic types of material: insulators, semiconductors, and metals. Finding new ways to condense the size of these materials is a persistent goal of the scientific community, with increasingly smaller electronics opening many new possibilities in device efficiency and capability. We aim to aid that endeavor by improving methods of selectively transforming regions of molybdenum di-sulfide (MoS2) from its semiconductor phase into its metal phase. Using a 50 kV electron beam at 500 pA, we directly expose thin flakes of exfoliated MoS2 on a SiO2 substrate, to a variety of electron beam doses to create patterns of metallic regions. We use atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) to spatially map changes in topography and work function respectively. Our results show that all physical changes occur in the SiO2 substrate while work function changes occur only in the MoS2. Changes in the work function are consistent with our expectations for a structural phase transition in MoS2 where the crystal lattice enters a higher energy configuration while energetic injected electrons can fall to lower energy states. The resulting metallic phase reduces its total energy and remains stable. This work paves the way to mono-material electronic devices, which will drastically both save space and material costs. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D46.00008: Enhancing the efficiency of FRET using surface plasmons waves on gold nanogratings Evan T Engelhaupt Our lab seeks to enhance the Förster resonance energy transfer (FRET) efficiency using surface plasmons excited on gold nanogratings. Surface plasmons are longitudinal oscillations of conduction electrons that travel along a metal surface. FRET is the transfer of energy between a donor and an acceptor fluorescent molecule, the efficiency of which is strongly dependent on the distance between the donor and acceptor molecules. Additionally, we suspect the surface plasmon enhancement effectiveness depends on the distance between the donor and acceptor and the grating surface. To precisely position the donor and acceptor molecules relative to each other and the gold nanograting, we developed a protocol to use double-stranded DNA as scaffolding. In this work, we varied the distance between the donor and acceptor molecules by adding additional base pairs between them along the same strand of the DNA backbone. The DNA is tethered to the gold nanograting via a thiol attachment to one terminating end. The donor and acceptor molecules were positioned at differing lengths from the nanograting, with the donor positioned closer to the surface. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D46.00009: Enhancing FRET Efficiency of Precisely Spaced Fluorescent Molecules Using Surface Plasmons Andra Key, Evan T Engelhaupt, Jennifer M Steele This project explores using surface plasmon waves excited on nanopatterned gold surfaces to enhance the efficiency of Förster Resonance Energy Transfer (FRET) between donor and acceptor fluorescent molecules. Surface plasmons are known to enhance fluorescence efficiency by altering the local density of optical states. Gold nanogratings were fabricated using a template stripping method. Following fabrication, the nanogratings are characterized. First we measured the topology using an atomic force microscope to ensure proper transferring of the nanopattern. Then we used white light spectroscopy to map out varying wavelengths of surface plasmons as a function of the angle of incident light. Following characterization, DNA with attached donor and acceptor fluorescent molecules were then deposited on viable samples. The DNA ensures the precise distance between the fluorescent molecules can be known, both in relation to each other and to the surface of the substrates. In this talk we will discuss optimizing the distance between the molecules and the gold surface for FRET enhancement. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D46.00010: Critical correlations and entanglement in the measured quantum Ising model Rohith Sajith, Zack Weinstein, Samuel J Garratt, Ehud Altman While the low-energy properties of one-dimensional quantum critical states are well understood, it is an ongoing problem to determine how they respond to local measurements, which can have highly non-local effects due to the underlying power-law correlations. To approach this question, we analytically and numerically investigate the effect of performing an extensive number of local measurements on the ground state of the critical quantum Ising model. Using exact free fermion numerics and analytical field-theoretic arguments, we show that parity-preserving local measurements do not modify the long-distance behavior of measurement-averaged physical quantities. In contrast, we identify a particular class of post-measurement quantum states whose correlations are dramatically altered: the exponents governing power-law correlations and the effective central charge appearing in the entanglement entropy are shown to vary continuously with the measurement rate. This work reveals the kinds of quantum critical correlations which survive measurement, and further develops a theoretical framework that can be applied to a wide class of measured quantum systems. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D46.00011: Quantum Fluctuations of the Dipole Moment of Electronic Systems as Conductivity Probes; Quantitative Ground State Computations in the Hubbard Model Sobhan Sayadpour, Ettore Vitali We accurately compute correlation functions involving the dipole moment of the electrons in the Hubbard model to study fermion localization in quantum many-body systems, as suggested in Phys. Rev. Lett. 82, 370 (1999) and Eur. Phys. J. B 79, 121 (2011). Leveraging the exact solution in the one-dimensional case, we assess our ability to use such correlation functions as probes for conductivity. In particular, we address the minimum value of the gap that can lead to the proper classification of a system as an insulator by numerically studying finite systems through correlated methodologies such as Quantum Monte Carlo. We discuss the technical difficulties, including the shell effects and potential limitations in higher dimensional models. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D46.00012: Finite Element Calculations of the Electron-Electron Coulomb Repulsions in a Quantum Dot Dimer Jessica K Jiang, Maicol A Ochoa, Garnett W Bryant
|
Monday, March 6, 2023 5:24PM - 5:36PM |
D46.00013: Spin and Charge Currents from Stern-Gerlach-Like Forces Emma Z Kurth, Lana Flanigan, Dana Coleman, Nicholas J Harmon In this work we study the influence of non-uniform magnetic fields on spin and charge dynamics in semiconductors. To do so, we solve a set of drift-diffusion equations which incorporate effects of electric and magnetic fields, spin relaxation, and field gradients. In some simple scenarios we find analytic solutions for both time-dependent and steady state conditions. More generally, we numerically solve a set of coupled ordinary or partial differential equations. Our conclusions are that both charge and pure spin currents can be generated by the Stern-Gerlach-like forces arising from a magnetic field with a constant gradient. Lastly, we introduce spin Hall and inverse spin Hall effects into our model to determine how they may amplify or obscure the Stern-Gerlach-like driven effects. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D46.00014: Design of a Cryogenic-Friendly Spintronic Terahertz Emitter Mount for Small Samples Alex D Giovannone, Yufei Li, Rolando Valdes Aguilar
|
Monday, March 6, 2023 5:48PM - 6:00PM |
D46.00015: Topological properties of photon-mediated interacting fermions in the presence of honeycomb optical lattice. Andrew Zimmerman, Theja DeSilva We study the effect of cavity-induced long-range interactions and laser-induced tunneling on the topological properties of fermions subjected to an optical lattice. We integrate out the bosonic degrees of freedom and use a mean-field theory to develop an effective fermionic Hamiltonian. Further, treating the attractive onsite interaction using a mean-field level, we study the band structure to investigate the topological properties of the system. We categorize the topological features by calculating the Chern number. |
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