Bulletin of the American Physical Society
2019 Annual Meeting of the APS Four Corners Section
Volume 64, Number 16
Friday–Saturday, October 11–12, 2019; Prescott, Arizona
Session B05: Condensed Matter Physics I |
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Chair: Anna Zaniewski, ASU Room: AC1 104 |
Friday, October 11, 2019 10:30AM - 10:42AM |
B05.00001: Differentiating Between Different Nonlinear Excitation Terahertz Pathways Through the Use of Two-Dimensional Spectroscopy Aldair Alejandro, Brittany E. Knighton, R. Tanner Hardy, Lauren M. Rawlings, Megan F. Nielson, Jeremy A. Johnson Intense, short pulses of terahertz (THz) radiation has made it possible to study and manipulate the properties of materials on ultrafast (\textless 1 ps) time scales. As with any region of the electromagnetic spectrum, intense terahertz pulses can induce nonlinear excitation pathways. In order to understand how THz pulses can be used to manipulate structure in solids, it is of great interest to understand the process or processes that cause this type of nonlinear behavior. In this work, Raman-active modes in a CdWO$_{\mathrm{4}}$ crystal are nonlinearly excited. With single-pulse (one-dimensional) THz measurements, we cannot distinguish between nonlinear photonic (two-photon absorption) and nonlinear phononic (anharmonic coupling between vibrational modes) processes. We show that two-dimensional (2D) spectroscopy allows us to identify the main nonlinear excitation pathway (two-photon absorption), and by making slight (but significant) changes to the experimental setup, we can isolate the secondary excitation pathway (anharmonic coupling). The nonlinear phononic (anharmonic coupling) pathway has been posited with theoretical work, but never before experimentally confirmed. [Preview Abstract] |
Friday, October 11, 2019 10:42AM - 10:54AM |
B05.00002: Numerical Calculations of the Superconducting Superheating Field within Eilenberger Theory Alden Pack, Mark Transtrum The superheating field (Hsh) is the largest applied field a type ii superconductor can withstand before magnetic vortices nucleate. The movement of magnetic vortices in AC fields dissipates heat and can lead to quenching (a loss of superconductivity). This is a major bottleneck for superconducting resonant frequency cavities used in particle accelerators. Previously Hsh has been calculated using Ginzburg-Landau theory, which is valid close to the critical temperature (Tc). The operating temperature of SRF cavities is significantly lower than Tc. We calculate Hsh using Eilenberger in the clean limit, which is valid for general temperatures. This is done by first solving the Ginzburg-Landau equations for an initial guess of the order parameter and magnetic potential vector. We then numerically solve for when the first variation of the Eilenberger free energy is zero and then use the second variation to evaluate Hsh. We show that our calculations close to Tc match the results of Ginzburg-Landau theory. [Preview Abstract] |
Friday, October 11, 2019 10:54AM - 11:06AM |
B05.00003: Ginzburg-Landau simulations of Nb3Sn in large magnetic fields Braedon Jones, Mark Transtrum Superconducting resonance cavities are used in particle accelerators to accelerate beams of charged particles to near light speed. The fundamental limit to performance in these cavities is the maximum induced magnetic field that the superconductors can expel. Traditionally, cavities have been made from Niobium; however, current technology has nearly reached the theoretical limit of performance for Niobium-based cavities. To overcome these limitations, Nb3Sn is being explored as a potential next-generation material. In actual development of Nb3Sn cavities, material defects arise that may limit performance. We use time-dependent Ginzburg-Landau simulations to explore which types of defects may be especially detrimental. In this talk, I will focus on small region of excess Sn that have been observed below the surface in real Nb3Sn cavities. I show that these islands may affect performance if they are near the surface, but become irrelevant when they are more than a penetration depth below the interface. [Preview Abstract] |
Friday, October 11, 2019 11:06AM - 11:18AM |
B05.00004: Direct Comparison Between Multi-Dimensional Terahertz Vibrational Spectroscopies Brittany E. Knighton, Megan F. Nielson, R. Tanner Hardy, Aldair Alejandro, Lauren M. Rawlings, Jeremy A. Johnson Multidimensional terahertz (THz) spectroscopy is a powerful tool for understanding nonlinear excitation, coherent energy flow, and coupling between collective degrees of freedom on ultrafast time scales. With extreme vibrational excitation using high-field THz light, 2D THz spectroscopy can reveal how anharmonic mode coupling results in coherent energy transfer and ascertain the excitation pathways behind nonlinear sample responses. We directly compare 2D THz-THz transmission measurement to 2D THz-THz-Raman measurements and explore evidence of anharmonic coupling between phonon modes in beta-barium borate (BBO). We find that 2D THz-THz-Raman spectroscopy produces a richer spectrum, better signal to noise, and is compatible with thicker samples than 2D THz-THz measurements. We model the phonon mode couplings in BBO to begin to untangle the complex 2D spectral features. [Preview Abstract] |
Friday, October 11, 2019 11:18AM - 11:30AM |
B05.00005: The effect of x-ray illumination on magnetic domain memory in [Co/Pd] / IrMn multilayers Colby Walker, Mason Parkes, David Keavney, Eric Fullerton, Karine Chesnel We are studying the effect that illumination by coherent x-rays may have on magnetic domain memory (MDM) in a [Co / Pd] / IrMn multilayers. MDM is the ability of the magnetic domains to retain their exact same domain topology upon field cycling. Earlier studies have suggested that under higher dose of x-ray illumination, the material may lose its existing MDM. To investigate this potential effect, we have used both x-ray resonant magnetic scattering (XRMS) along with magneto-transport measurements to track the exchange bias while the sample is illuminated with x-rays. Magneto-transport is here used to measure the hysteresis loop of our multilayers material from which we can measure the exchange bias and its possible alteration. A loss of exchange bias would indicate that the x-rays illumination dose may alter the strength of the exchange couplings and ultimately the amount of MDM. Knowing if a loss of exchange bias has occurred requires collecting magneto-transport data as well as XRMS data and correlating the observed changes under various dose of x-ray illumination. [Preview Abstract] |
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