Physics Commons^™

Measurement Of Speed Of Sound Using Smartphones, Omotolani Adelekan

Publications and Research

The goal of this experiment is to determine the speed of sound in air. To measure the speed of sound, I used two smartphones and an app called Phyphox This app uses the microphone of the smartphone to detect the time between two acoustic events The “acoustic stopwatch” tool on the app is used to measure the time between two sound signals These two signals are produced by hand clapping In this experiment, the speed of sound is determined using the time of flight method This method is based on measuring the time delay between the generation and the detection …

Role Played By Edge-Defects In The Optical Properties Of Armchair Graphene Nanoribbons, Thi-Nga Do, Godfrey Gumbs, Danhong Huang, Bui D. Hoi, Po-Hsin Shih

Publications and Research

We explore the implementation of specific optical properties of armchair graphene nanoribbons (AGNRs) through edge-defect manipulation. This technique employs the tight-binding model in conjunction with the calculated absorption spectral function. Modification of the edge states gives rise to the diverse electronic structures with striking changes in the band gap and special flat bands at low energy. The optical-absorption spectra exhibit unique excitation peaks, and they strongly depend on the type and period of the edge extension. Remarkably, there exist the unusual transition channels associated with the flat bands for selected edge-modified systems. We discovered the special rule governing how the …

Tailoring Plasmon Excitations In Alpha − T 3 Armchair Nanoribbons, Andrii Iurov, Liubov Zhemchuzhna, Godfrey Gumbs, Danhong Huang, Paula Fekete, Farhana Anwar, Dipendra Dahal, Nicholas Weekes

Publications and Research

We have calculated and investigated the electronic states, dynamical polarization function and the plasmon excitations for α − T ₃ nanoribbons with armchair-edge termination. The obtained plasmon dispersions are found to depend significantly on the number of atomic rows across the ribbon and the energy gap which is also determined by the nanoribbon geometry. The bandgap appears to have the strongest effect on both the plasmon dispersions and their Landau damping. We have determined the conditions when relative hopping parameter α of an α − T ₃ lattice has a strong effect on the plasmons which makes our material distinguished …

Wave Function Identity: A New Symmetry For 2-Electron Systems In An Electromagnetic Field, Marlina Slamet, Viraht Sahni

Publications and Research

Stationary-state Schrödinger-Pauli theory is a description of electrons with a spin moment in an external electromagnetic field. For 2-electron systems as described by the Schrödinger-Pauli theory Hamiltonian with a symmetrical binding potential, we report a new symmetry operation of the electronic coordinates. The symmetry operation is such that it leads to the equality of the transformed wave function to the wave function. This equality is referred to as the Wave Function Identity. The symmetry operation is a two-step process: an interchange of the spatial coordinates of the electrons whilst keeping their spin moments unchanged, followed by an inversion. The Identity …

Experimental Observation Of Topological Z2 Excitonpolaritons In Transition Metal Dichalcogenide Monolayers, Mengyao Li, Ivan Sinev, Fedor Benimetskiy, Tatyana Ivanova, Ekaterina Khestanova, Svetlana Kiriushechkina, Anton Vakulenko, Sriram Guddala, Maurice Skolnick, Vinod M. Menon, Dmitry Krizhanovskii, Andrea Alù, Anton Samusev, Alexander B. Khanikaev

Publications and Research

The rise of quantum science and technologies motivates photonics research to seek new platforms with strong light-matter interactions to facilitate quantum behaviors at moderate light intensities. Topological polaritons (TPs) offer an ideal platform in this context, with unique properties stemming from resilient topological states of light strongly coupled with matter. Here we explore polaritonic metasurfaces based on 2D transition metal dichalcogenides (TMDs) as a promising platform for topological polaritonics. We show that the strong coupling between topological photonic modes of the metasurface and excitons in TMDs yields a topological polaritonic Z₂ phase. We experimentally confirm the emergence of one-way …

Direct Observation Of Chaotic Resonances In Optical Microcavities, Shuai Wang, Shuai Liu, Yilin Liu, Shumin Xiao, Zi Wang, Yubin Fan, Jiecai Han, Li Ge, Qinghai Song

Publications and Research

Optical microcavities play a significant role in the study of classical and quantum chaos. To date, most experimental explorations of their internal wave dynamics have focused on the properties of their inputs and outputs, without directly interrogating the dynamics and the associated mode patterns inside. As a result, this key information is rarely retrieved with certainty, which significantly restricts the verification and understanding of the actual chaotic motion. Here we demonstrate a simple and robust approach to directly and rapidly map the internal mode patterns in chaotic microcavities. By introducing a local index perturbation through a pump laser, we report …

Evaluation Of Log P, Pka, And Log D Predictions From The Sampl7 Blind Challenge, Teresa Danielle Bergazin, Nicolas Tielker, Yingying Zhang, Junjun Mao, M. R. Gunner, Karol Francisco, Carlo Ballatore, Stefan M. Kast, David L. Mobley

Publications and Research

The Statistical Assessment of Modeling of Proteins and Ligands (SAMPL) challenges focuses the computational modeling community on areas in need of improvement for rational drug design. The SAMPL7 physical property challenge dealt with prediction of octanol-water partition coefficients and pK_a for 22 compounds. The dataset was composed of a series of N-acylsulfonamides and related bioisosteres. 17 research groups participated in the log P challenge, submitting 33 blind submissions total. For the pK_a challenge, 7 different groups participated, submitting 9 blind submissions in total. Overall, the accuracy of octanol-water log P predictions in the SAMPL7 challenge was …

Protein Motifs For Proton Transfers That Build The Transmembrane Proton Gradient, Divya Kaur, Umesh Khaniya, Yingying Zhang, M. R. Gunner

Publications and Research

Biological membranes are barriers to polar molecules, so membrane embedded proteins control the transfers between cellular compartments. Protein controlled transport moves substrates and activates cellular signaling cascades. In addition, the electrochemical gradient across mitochondrial, bacterial and chloroplast membranes, is a key source of stored cellular energy. This is generated by electron, proton and ion transfers through proteins. The gradient is used to fuel ATP synthesis and to drive active transport. Here the mechanisms by which protons move into the buried active sites of Photosystem II (PSII), bacterial RCs (bRCs) and through the proton pumps, Bacteriorhodopsin (bR), Complex I and Cytochrome …

Defining The Basis Of Cyanine Phototruncation Enables A New Approach To Single-Molecule Localization Microscopy, Siddharth S. Matikonda, Dominic A. Helmerich, Mara Meub, Gerti Beliu, Philip Kollmannsberger, Alexander Greer, Markus Sauer, Martin J. Schnermann

Publications and Research

The light-promoted conversion of extensively used cyanine dyes to blue-shifted emissive products has been observed in various contexts. However, both the underlying mechanism and the species involved in this photoconversion reaction have remained elusive. Here we report that irradiation of heptamethine cyanines provides pentamethine cyanines, which, in turn, are photoconverted to trimethine cyanines. We detail an examination of the mechanism and substrate scope of this remarkable twocarbon phototruncation reaction. Supported by computational analysis, we propose that this reaction involves a singlet oxygeninitiated multistep sequence involving a key hydroperoxycyclobutanol intermediate. Building on this mechanistic framework, we identify conditions to improve the …

Luminescence Properties Of Hexagonal Boron Nitride Powders Probed By Deep Uv Photoluminescence Spectroscopy, Nikesh Maharjan, Mim Lal Nakarmi

Publications and Research

Deep ultraviolet (UV) photoluminescence (PL) spectroscopy was employed to study the luminescence properties of hexagonal boron nitride (h-BN) crystal powders after annealing the samples at different temperatures in the range of 100–900 ÅãC for 1 h in ambient air. The PL spectrum from the h-BN powder samples annealed around 700 ÅãC showed strong luminescence intensity at 5.49 eV along with enhanced phonon-assisted band-edge emission at 5.90 eV. Additionally, it revealed sharp atomic-like emission lines in UV region at 4.10, 4.12, 4.14, and 4.16 eV with line widths less than 1 nm from the annealed samples which were not present in …

Enhanced Nonlinear Interaction Of Polaritons Via Excitonic Rydberg States In Monolayer Wse2, Jie Gu, Valentin Walther, Lutz Waldecker, Daniel Rhodes, Archana Raja, James C. Hone, Tony F. Heinz, Stéphane Kéna-Cohen, Thomas Pohl, Vinod M. Menon

Publications and Research

Strong optical nonlinearities play a central role in realizing quantum photonic technologies. Exciton-polaritons, which result from the hybridization of material excitations and cavity photons, are an attractive candidate to realize such nonlinearities. While the interaction between ground state excitons generates a notable optical nonlinearity, the strength of such interactions is generally not sufficient to reach the regime of quantum nonlinear optics. Excited states, however, feature enhanced interactions and therefore hold promise for accessing the quantum domain of single-photon nonlinearities. Here we demonstrate the formation of exciton-polaritons using excited excitonic states in monolayer tungsten diselenide (WSe₂) embedded in a …

Alternative View Of Oxygen Reduction On Porous Carbon Electrocatalysts: The Substance Of Complex Oxygen-Surface Interactions, Giacomo De Falco, Marc Florent, Jacek Jagiello, Yongqiang Cheng, Luke L. Daemen, Anibal J. Ramirez-Cuesta, Teresa J. Bandosz

Publications and Research

Electrochemical oxygen reduction reaction (ORR) is an important energy-related process requiring alternative catalysts to expensive platinum-based ones. Although recently some advancements in carbon catalysts have been reported, there is still a lack of understanding which surface features might enhance their efficiency for ORR. Through a detailed study of oxygen adsorption on carbon molecular sieves and using inelastic neutron scattering, we demonstrated here that the extent of oxygen adsorption/interactions with surface is an important parameter affecting ORR. It was found that both the strength of O2 physical adsorption in small pores and its specific interactions with surface ether functionalities in the …

Dipolariton Propagation In A Van Der Waals Tmdc With Ψ-Shaped Channel Guides And Buffered Channel Branches, Patrick Serafin, German Kolmakov

Publications and Research

Using a computational approach based on the driven diffusion equation for a dipolariton wave packet, we simulate the diffusive dynamics of dipolaritons in an optical microcavity embedded with a transition metal dichalcogenide (TMDC) heterogeneous bilayer encompassing a Ψ-shaped channel. By considering exciton dipolaritons, which are a three way superposition of direct excitons, indirect excitons and cavity photons; we are able to drive the dipolaritons in our system by the use of an electric voltage and investigate their diffusive properties. More precisely, we study the propagation of dipolaritons present in a MoSe₂-WS₂ heterostructure, where the dipolariton propagation is …

Superfluid Swimmers, German Kolmakov, Igor S. Aranson

Publications and Research

The propulsion of living microorganisms ultimately relies on viscous drag for body-fluid interactions. The self-locomotion in superfluids such as ⁴He is deemed impossible due to the apparent lack of viscous resistance. Here, we investigate the self-propulsion of a Janus (two-face) light-absorbing particle suspended in superfluid helium ⁴He (He-II). The particle is energized by the heat flux due to the absorption of light from an external source. We show that a quantum mechanical propulsion force originates due to the transformation of the superfluid to a normal fluid on the heated particle face. The theoretical analysis is supported by the …

Triplet 23S State Of A Quantum Dot In A Magnetic Field: A 'Quantal Newtonian' First Law Study, Marlina Slamet, Viraht Sahni

Publications and Research

The triplet 2³S state of a 2-electron 2-dimensional quantum dot in a magnetic field is studied via a complementary perspective of Schrödinger-Pauli theory. The perspective is that of the individual electron via its equation of motion or ‘Quantal Newtonian’ first law. According to the law, each electron experiences an external and internal field, the sum of which vanishes. The external field is the sum of the binding and Lorentz fields. The internal field is a sum of the electron-interaction, kinetic, differential density, and internal magnetic fields. The energy is expressed in integral virial form in terms of these …

Vibration Of A Cantilever Laboratory, Mark D. Shattuck

Open Educational Resources

Hands on laboratory to measure the vibrational frequencies of a cantilever.

Follow this hyperlink for quick access to activity

Toward Transformable Photonics: Reversible Deforming Soft Cavities, Controlling Their Resonance Split And Directional Emission, Mark Douvidzon, Shai Maayani, Harel Nagar, Tamir Admon, Vladimir Shuvayev, Lan Yang, Lev Deych, Yael Roichman, Tal Carmon

Publications and Research

We report on reversible and continuously deformable soft micro-resonators and the control of their resonance split and directional emission. Assisted by computerized holographic-tweezers, functioning as an optical deformer of our device, we gradually deform the shape and change the functionality of a droplet whispering-gallery cavity. For example, we continuously deform hexagonal cavities to rectangular ones and demonstrate switching to directionally emitting mode-of-operation, or splitting a resonant mode to a 10-GHz separated doublet. A continuous trend of improving spatial light modulators and tweezers suggests that our method is scalable and can control the shape and functionality of many individual devices. We …

Transmission Zeros With Topological Symmetry In Complex Systems, Yuhao Kang, Azriel Genack

Publications and Research

Understanding vanishing transmission in Fano resonances in quantum systems and metamaterials and perfect and ultralow transmission in disordered media, has advanced the understanding and applications of wave interactions. Here we use analytic theory and numerical simulations to understand and control the transmission and transmission time in complex systems by deforming a medium and by adjusting the level of gain or loss. Unlike the zeros of the scattering matrix, the position and motion of the zeros of the determinant of the transmission matrix in the complex plane of frequency and field decay rate have robust topological properties. In systems without loss …

Dynamics Of Transmission In Disordered Topological Insulators, Yuhao Kang, Yiming Huang, Azriel Genack

Publications and Research

Robust transmission in topological insulators makes it possible to steer waves without attenuation along bent paths within imperfectly fabricated photonic devices. But the absence of reflection does not guarantee the fidelity of pulsed transmission which is essential for core photonic functionalities. Pulse transmission is disrupted by localized modes in the bulk of topological insulators which coexist with the continuum edge mode and are pushed deeper into the band gap with increasing disorder. Here we show in simulations of the Haldane model that pulse propagation in disordered topological insulators is robust throughout the central portion of the band gap where localized …

Exclusion Statistics For Particles With A Discrete Spectrum, Stéphane Ouvry, Alexios P. Polychronakos

Publications and Research

We formulate and study the microscopic statistical mechanics of systems of particles with exclusion statistics in a discrete one-body spectrum. The statistical mechanics of these systems can be expressed in terms of effective single-level grand partition functions obeying a generalization of the standard thermodynamic exclusion statistics equation of state. We derive explicit expressions for the thermodynamic potential in terms of microscopic cluster coefficients and show that the mean occupation numbers of levels satisfy a nesting relation involving a number of adjacent levels determined by the exclusion parameter. We apply the formalism to the harmonic Calogero model and point out a …