Bulletin of the American Physical Society
Fall 2021 Meeting of the Eastern Great Lakes Section
Volume 66, Number 15
Friday–Saturday, November 12–13, 2021; Virtual; Eastern Time
Session J03: Oral Session 3 |
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Chair: Bhubanjyoti Bhattacharya, Lawrence Technological University |
Saturday, November 13, 2021 10:15AM - 10:30AM |
J03.00001: Optical properties of massive anisotropic tilted Dirac systems Miguel Mojarro Ramirez We explore the effect of valley-contrasting gaps in the optical response of two-dimensional anisotropic tilted Dirac systems. The energy bands present an indirect gap in each valley with a reduced magnitude with respect to the nominal gap of the untilted system. Thus, a new possibility opens for the position of the Fermi level (an “indirect zone”) and for the momentum space available for allowed transitions. We study the spectrum of interband transitions through the joint density of states, which displays a set of van Hove singularities depending on the Fermi energy. This same quantity determines the prominent structure of the optical conductivity tensor. The longitudinal conductivity illustrates the strong anisotropy of the optical response. The breaking of valley symmetry leads to a finite Hall response and associated optical properties. The anomalous and valley Hall conductivities present graphene-like behavior, with characteristic modifications due to the indirect zones. We also calculate the spectra of optical opacity and polarization rotation, which can reach magnitudes of tenths of radians in some cases. The spectral features of the calculated response properties suggest optical ways to determine the formation of different gaps in such class of Dirac systems. [Preview Abstract] |
Saturday, November 13, 2021 10:30AM - 10:45AM |
J03.00002: First-principles study of LiAlO$_{2}$ in tetrahedrally and octahedrally coordinated structures Phillip Popp, Walter Lambrecht Ultrawide-band gap (UWBG) semiconductors (band gap \textgreater 4 eV) have many potential interesting applications, such as in high-power electronics and deep-UV optoelectronic devices. LiAlO$_{2}$~is a candidate material for UWBG semiconductors. This project is a first-principles electronic structure study of LiAlO$_{2}$, focusing on band gap/band structure, bulk moduli of common crystal structures, and transition pressures between different structures. Specifically, we compare the tetragonal~$\gamma $ and orthorhombic~$\beta $ structures (both tetrahedrally coordinated) with the octahedrally coordinated R-3m~$\alpha $ structure. We calculate these properties using the density functional theory (DFT)-based linearized muffin tin orbital (LMTO) and pseudopotential plane wave methods. We find that the tetrahedrally bonded structures have slightly lower energy than the octahedral one and a transition to the octahedral phase occurs near 1.5 GPa. [Preview Abstract] |
Saturday, November 13, 2021 10:45AM - 11:00AM |
J03.00003: Deformation induced magnetic confinement and isolated flat-bands in graphene Md Tareq Mahmud Strain-induced deformations can alter the charge distribution in graphene and hence provide a new way to design its band structure and transport properties. Working with quasi-periodic linear and close-packed Gaussian deformations, we showed that a pseudo-magnetic produces charge confinement at desired locations in graphene. We also found that spatial maps of the density of states exhibit periodic structures known as moir\'{e} patterns [1]. Motivated by these results, we study graphene with different superlattice structures induced by periodic cosine-like deformations and square, triangular and rectangular symmetries. Our analysis shows that it is possible to create isolated flat bands when the superlattice breaks graphene's parity symmetry (sublattice symmetry). The geometry of the substrate controls the flatness of the isolated bands. Our findings can be used to guide potential experimental realizations to produce flat-band systems by design. \underline {[1] Phys. Rev. B 102, 235410(2020)} [Preview Abstract] |
Saturday, November 13, 2021 11:00AM - 11:15AM |
J03.00004: Double Quantum Dot Qubits in Microwave Cavities Matthew McGreal Fabrication of coherent qubits and scalability schemes are essential for the realization of quantum computers. Electron spins in semiconductors make promising qubits because of their long coherence times (ms) compared to gate operation timescales (ns). Additionally, a photon cavity can mediate long-range interactions between spins and allow for non-destructive measurements of the qubit state using the transmission through the cavity. Combining these effects makes an electron spin in a double quantum dot (DQD) coupled to a microwave cavity a good candidate for a qubit with the potential for scalability. As shown [0], a single electron in a DQD creates a dipole moment that can be coupled to the spin degree of freedom in the presence of magnetic fields, leading to strong spin-photon coupling. This project explores qubits systems containing 1, 2, and 3 double quantum dots inside a microwave cavity. Having reproduced theoretical results for systems containing 1 [1] and 2[2] qubits, I analyze the transmission amplitude, including a third DQD qubit, and discuss the resulting limitations of this scalability method. [0] M. Benito et al. In: Phys. Rev. B 96 (23 Dec. 2017), p. 235434. [1] Guido Burkard et al. In: Nature Reviews Physics 2.3 (Jan. 2020), pp. 129-- 140. issn: 2522-5820. [2] F. Borjans et al. In: Nature 577 (7789 2020), pp. 195--198. [Preview Abstract] |
Saturday, November 13, 2021 11:15AM - 11:30AM |
J03.00005: X-ray reflectivity study to investigate the nanoscale structure of atmospheric plasma polymerized films Brenna Rossi, Cagatay Yilmazoglu, Mark D. Foster Atmospheric plasma polymerized (APP) films' deposition, physical properties, and chemical composition have been well-studied due to interest regarding their versatility. However, the nanoscale structure of APP films has never been thoroughly probed with respect to depth. We report X-ray reflectivity curves of atmospheric plasma polymers (APP) deposited from hexamethyldisiloxane (HMDSO) at varying plasma power levels and levels of relative humidity. The reflectivity datasets were all well-fitted with 3-layer models featuring a thick, higher scattering length density (SLD) ``bulk'' layer between two thinner, lower SLD layers at the substrate and air interfaces. For films deposited at low humidity, the SLD of the bulk layer decreases with increased power level applied to the plasma during deposition, but increased humidity curtails this sensitivity to power. The bulk layer SLDs are the same across power levels at higher humidity. [Preview Abstract] |
Saturday, November 13, 2021 11:30AM - 11:45AM |
J03.00006: Electrical scanned probe microscopy impedance model reveals transient photoconductivity in a Ruddlesden-Popper 2D lead-halide perovskite Ryan Dwyer, John Marohn Electrical force microscopy (EFM) experiments such as Kelvin probe force microscopy can locally measure semiconductor properties correlated with overall device performance and degradation. What sample properties are probed by these measurements, however, remains an open question. The typical model used to interpret these experiments incorrectly assumes that tip and sample charge responds instantaneously to changes in the applied tip-sample voltage. Dwyer, Marohn and coworkers developed an impedance model of KPFM that correctly accounts for tip-sample charge motion for both frequency-domain and time-resolved EFM experiments. As an application of the model, time and frequency-resolved electric force microscopy experiments were performed on a film of butylammonium lead iodide, a 2D Ruddlesden--Popper perovskite semiconductor. These experiments revealed the sample's transient photoconductivity, which had a rise time and decay time of $\sim 100\,\, \mu\text{s}$. To enable the broader community of KPFM users to use this powerful theory, we developed an open-source Python package and website that can simulate or fit experimental data using the model and information about the tip geometry and sample parameters. [Preview Abstract] |
Saturday, November 13, 2021 11:45AM - 12:00PM |
J03.00007: Analogue leptogenesis in chirped excitation Matthew Commons, Nicole Abend, Johnathon George, Ian Jones, Aaron Weiser, Michael Crescimanno The effective discrete conjugation symmetry that arises in the rotating wave frame of quantum optics is the analogue of the discrete symmetry "C" in field theory. Breaking this conjugation symmetry leads to a universal framework for understanding asymmetries between up- and down- chirped optical excitation in multilevel quantum systems. We explain the relevant quantum optics theory and our experiment using diode lasers and an atomic vapor cell that demonstrate the phenomenological correspondence to the simplest model of leptogenesis, the process by which our early universe allegedly evolved from equal amounts of matter and antimater to its present matter excess. [Preview Abstract] |
Saturday, November 13, 2021 12:00PM - 12:15PM |
J03.00008: Application of Monte Carlo Method to Simulate Radiation Transfer through Exoplanetary Atmospheres Michael Rothman, Anil Pradhan, Sultana Nahar, Bilal Shafique, Kevin Hoy Development is underway of an exoplanetary atmosphere simulator Geant4-EXOPlanets (G4-EXOP) based on Geant4, a Monte Carlo program package enabling modeling of radiation and particle transmission through matter. G4-EXOP will be a toolkit to model host-star radiation transmission through atmospheric layers utilizing atomic and molecular data, allowing the comparison of observations with simulated spectra. We focus on atomic biosignatures (H, C, N, etc.) and molecules containing them (H$_{2}$O, CO$_{2}$, etc). Phosphorus is a focus as abundances in stellar systems are vital for DNA-based life. Atomic transition data are calculated using SUPERSTRUCTURE (SS), with phosphorus results reported. Utilizing molecular data obtained through ExoMol, we report computed oscillator strengths for H$_{2}$O. We also report G4-EXOP filtered Gaussian convolutions of the solar irradiance and flux residual simulated spectra as a test. Following further development, we will simulate the flux residual and irradiance spectra of the Earth and Sun before simulating other star -- exoplanet pairs. G4-EXOP will be a toolkit for modeling host-star radiation transmission through exoplanet atmospheres to characterize biosignature abundances within observations. [Preview Abstract] |
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