Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P33: Spectroscopy and OxidesFocus
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Sponsoring Units: FIAP Chair: Harishankar Jayakumar, City College of New York Room: BCEC 204B |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P33.00001: Time-Domain Spectroscopy of Mesoscopic Conductors Using Voltage Pulses Pablo Burset, Janne Kotilahti, Michael Moskalets, Christian Flindt The development of single-electron sources are paving the way for a novel type of experiments in which individual electrons are emitted into a quantum-coherent circuit. However, to facilitate further progress towards fully coherent on-chip experiments with electrons, a detailed understanding of the quantum circuits is needed. We propose to perform time-domain spectroscopy of mesoscopic conductors by applying Lorentzian-shaped voltage pulses to an input contact. We show how characteristic timescales of a quantum-coherent conductor can be extracted from the distribution of waiting times between charge pulses propagating through the circuit. To illustrate our idea, we employ Floquet scattering theory to evaluate the electron waiting times for an electronic Fabry-Pérot cavity and a Mach-Zehnder interferometer. Our spectroscopic method benefits from the particle-like behavior of the charge pulses, while still being sensitive to their quantum statistics. This unique combination makes our scheme promising for the characterization of quantum-coherent circuits. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P33.00002: Dynamics of strongly coupled singlet fission molecules in optical microcavity Bin Liu, Matthew Y Sfeir, Vinod M Menon We have experimentally studied the dynamics of a singlet-fission molecule-metal microcavity system under strong coupling by using pump-probe transient absorption technique. Under one-photon pump, where the system is selectively pumped by wavelengths which are resonant with exciton, upper, and lower polariton, the dynamics of polariton states is found to be determined by that of the exciton, which has long-time character. Moreover, comparing to the neat film without cavity, the kinetics of the molecular triplet state is not significantly modified by strong singlet molecular exciton-photon coupling within the cavity. Under two-photon pump, short-time (sub-picosecond) dynamics is observed from both the polariton cavity system and solid-state neat film, indicating this results from the ultrafast optical response of the nonlinear organic molecules. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P33.00003: Measurement of Quadratic Terahertz Optical Nonlinearities Using Second-Harmonic Lock-in Detection Shuai Lin, Shukai Yu, Diyar Talbayev We present a method to measure quadratic terahertz optical nonlinearities in terahertz time-domain spectroscopy. We use a rotating linear polarizer (a polarizing chopper) to modulate the amplitude of the incident terahertz pulse train. We use phase-sensitive lock-in detection at the fundamental and the second harmonic of the modulation frequency to separate the materials’ responses that are linear and quadratic in a terahertz electric field. We demonstrate this method by measuring the quadratic terahertz Kerr effect in the presence of the much stronger linear electro-optic effect in the (110) GaP crystal. We propose that the method can be used to detect terahertz second-harmonic generation in noncentrosymmetric media in time-domain spectroscopy, with broad potential applications in nonlinear terahertz photonics and related technology. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P33.00004: Optical spectroscopy of emission from GeSn waveguides on Si Jay Mathews, Zairui Li, Elaheh Ghanati, John Kouvetakis, Jose Menendez, Imad Agha GeSn alloys are attractive for infrared emission due to the tunable band gap in the infrared and the quasi-direct or direct nature of the gap. Epitaxial growth of GeSn on Si has been demonstrated using multiple growth techniques and is now being incorporated into commercial device fabrication. Recently, laser emission from GeSn waveguides on Si has been demonstrated at temperatures up to 240 K, but the search for room temperature Si-based laser continues. In this work, we investigate the optical emission from optically-pumped GeSn waveguides at room temperature using optical spectroscopy. The results show that there is a highly nonlinear dependence on the total emission output power with respect to the input pump power. However, measurements of the emission spectrum do not show any narrowing of the emission peak, and Fabry-Perot measurements do not show any observable modes. Modeling of spontaneous emission from these materials indicates that the experimental power dependence can only be the result of optical gain in the GeSn. This result shows that optical gain at room temperature is possible. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P33.00005: The Physics of Optical Dispersion Equations William Karstens, David Smith We explore the disparate optical dispersion equations used to interpolate the refractive index from measurements at a limited number of spectral lines. Initial 19th-century formulations were based on elastic and electromagnetic theories. Subsequent developments were primarily empirical fits to optical-glass data and are misleading when applied to non-polar semiconductors. We show that the theoretical results of Cauchy, Sellmeier, etc., either classical or quantum-mechanical, follow from linear-response theory via the Kramers-Kronig relations regardless of the mechanism assumed. Their use is limited by the number of parameters required. In contrast, most empirical relations were chosen for simplicity and compatibility with classical ray-tracing. Their reliance on measurements in the visible blurs the roles of electronic and ionic polarization. Moreover, most empirical equations predict indices of odd parity in photon energy, in conflict with time-reversal invariance. A reformulation of the empirical dispersion equations consistent with linear-response theory corrects the parity error and clarifies their application to polar and non-polar materials. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P33.00006: Calculating form-dependent optical scattering at vacuum- and extreme-ultraviolet wavelengths off nanoelectronic structures Bryan Barnes, Mark-Alexander Henn, Hui Zhou, Martin Sohn, Rick Silver Form birefringence, where the orientation of periodic structures yields effective refractive index differences between orthogonal polarizations, is the basis for several applications including the successful detection of aperiodic imperfections (e.g., defects in nanoelectronics) at visible and ultraviolet wavelengths. As shorter wavelengths are employed by industry, the key assumption behind form birefringence - that the wavelength is larger than the periodicity - is challenged even with decreasing device dimensions. Here, the form dependence of high spatial-frequency scattering off periodic structures is numerically assessed among deep-, vacuum-, and extreme-ultraviolet illumination wavelengths (DUV, VUV, EUV). Form-dependent scattering intensity ratios of the scattering off ideal periodic arrays decrease with wavelength into the VUV, but dramatically increase for the 47 nm EUV wavelength due primarily to the wavelength-dependent optical properties of the dielectrics involved. After adding a bridging defect to this array, the 47 nm wavelength remains most sensitive to these patterning faults. These results should be extensible, not only to structures in nanoelectronics, but also to emerging engineered optical materials for DUV and shorter wavelengths. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P33.00007: Ab initio theory and calculations of many-body effects in photoemission from semiconductor surfaces: Cs3Sb as a case study Johannes Kevin Nangoi, Alice Galdi, Luca Cultrera, Ravishankar Sundararaman, Jared M. Maxson, Ivan V. Bazarov, Siddharth Karkare, Howard A Padmore, Tomas Arias Understanding the momentum distribution of photoemitted electrons is important for developing next-generation photoinjectors for electron microscopes and particle accelerators, where the photoelectron beams are required to be highly focused. We will describe a recently developed ab initio theory to predict the momentum distribution of photoelectrons as a function of photon energy, including many-body effects as needed. We then present our most recent results for Cs3Sb, which predict the (100) surface to provide highly focused photoelectron beams. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P33.00008: ABSTRACT WITHDRAWN
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Wednesday, March 6, 2019 4:06PM - 4:18PM |
P33.00009: Hydrothermal Growth of zinc oxide nano-rods doped with manganese Rajni Bagga, Vo-Van Truong, Pablo Bianucci We synthesised ZnO Nanorods arrays doped with and without Mn doping (at a 1% concentration of the precursor salts) by a hydrothermal method at low temperature. They were characterised by scanning electron microscopy (SEM), Photoluminescence (PL) and electron paramagnetic (EPR) spectroscopy. All samples produced broad band Photoluminescence (PL) emissions in the yellow-orange-red range, typically attributed to defects in the crystalline structure. The PL spectra does not seem to show significant changes in the ratio of the near band edge emission and the defect emission with the Mn doping. From this, we infer that the crystal quality of the ZnO nanorods does not change with Mn doping. The EPR spectrum from the ZnO nanoparticles formed in the growth solution confirms the presence of Mn in them. We use Micro-Raman spectroscopy to investigate the local crystal structure of the nanomaterials. Room temperature micro-Raman spectra confirms the wurtzite structure. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P33.00010: Evaluating Zn1-xCdxO thin films as transparent conducting oxides Omar Aguilar, Suelen De Castro, Marcio P. F. Godoy, Mariama Rebello Sousa Dias Zn1−xCdxO thin films spanning the whole composition range have widely been explored as active region in optoelectronic devices. The precise control of the Cd concentration as well as its crystalline phase allowed to fully characterize their intrinsic properties. However, its application as a transparent conducting oxide material (TCO) is promising, and a complete analysis of this application is still missing. Here, we fabricated Zn1−xCdxO thin films via the spray pyrolysis method and confirmed their composition via Energy-dispersive X-ray spectroscopy (EDX) measurements. Also, we characterized the electric and optical properties through spectroscopy ellipsometry and transmittance measurements from 300 nm to 3200 nm wavelength range. As expected, we see a nonlinear red-shift of the optical band gap while increasing the Cd concentration. Moreover, we show that the thin films have an average transmittance of 0.8 over a wide range of the electromagnetic spectrum. We find that most of our samples were conductive with a sheet resistance as low as 19.8 Ω for a composition of Zn0.25Cd0.75O. The use of alloyed metal oxides as building blocks for organic solar cells with photonic crystal structures will also be discussed. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P33.00011: Hysteresis response of 2D electron nematics in the presence of material disorder Sayan Basak, Erica Carlson, Karin Andrea Dahmen Electron nematic phases, which break the rotational symmetry of the host crystal while retaining liquidity, have been observed in a variety of systems, including strontium ruthenates, iron superconductors, cuprate superconductors, the (111) surface of bismuth, and high fractional Landau levels. Depending upon interactions with the lattice, the nematic may either be in the XY or the Ising universality class. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P33.00012: Supersonic propagation of atomic motion by phasons in fresnoite Michael Manley, Paul J Stonaha, Douglas L Abernathy, Songxue Chi, Raffi Sahul, Raphael Hermann, John D Budai Our recent inelastic neutron scattering measurements reveal that waves of atomic motion propagate at surprisingly high speeds of up to 4.3 times the speed of sound in the form of phasons in the piezoelectric mineral fresnoite (Ba2TiSi2O8). Phasons are quasiparticles that exist because of an incommensurate modulation (or ‘wrinkles’) in the flexible framework structure of fresnoite. They are associated with atomic rearrangements that change the phase of waves describing the incommensurate modulation. Phasons are usually overdamped and move diffusively, and are thus much slower than phonons (vibrations involving the translation of atoms, rather than rearrangements). However, the phasons in fresnoite are found not to be overdamped owing to a characteristic rotation of the phasons away from the driving soft phonon, yielding the supersonic propagation. These supersonic phasons enhance thermal conductivity and channel lattice energy at speeds well beyond the limits of phonons. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P33.00013: Effects of substitutional defects on the thermal-physical properties of Gd2Zr2O7 pyrochlores Fengai Zhao, Xian-Ming Bai, Haiyan Xiao, Xiaotao Zu Rare-earth pyrochlores, particularly Gd2Zr2O7, have been proposed as promising candidates for the next-generation thermal barrier coatings (TBCs) due to their good structural stability, low thermal conductivities at high temperatures. In this work, systematic studies of the incorporation of Yb3+, Nd3+, La3+, Ti4+, Hf4+, Ce4+ into cation sites in Gd2Zr2O7 has been investigated by density functional theory (DFT) calculations to explore the underlying mechanisms for modifying its thermal-physical properties. Among these doped cations, incorporation of oversized Ce4+ at the Zr-site leads to significantly smaller Young’s modulus, better ductility, smaller Debye temperature, and lower thermal conductivity. In particular, the thermal conductivity of Ce-doped Gd2Zr2O7 decreases as large as 21 % with the complete Ce substitution based on the Clarke’s model. The incorporation of oversized Ce cations weakens the interatomic bonds, which is the main factor for the improved thermal-physical properties of Gd2Zr2-yCeyO7 pyrochlores. The results provide theoretical predictions of the behavior and performance of pyrochlores at high temperatures and may promote experimental investigation in the future. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P33.00014: Investigations on the Electronic and Optical Properties of Double Perovskites Ba2BiSbO6 Bishnu Prasad Belbase, Shalika Ram Bhandari, Gopi Chandra Kaphle, Madhav Prasad Ghimire, Dinesh Kumar Yadav Recent research on double perovskites with large spin-orbit coupling (SOC) assisted materials are of great interest due to their novel properties. Materials with band gap in the visible range are found suitable for opto-electronic devices. Depending on the types of gaps (indirect or direct), materials can be used for photo detectors or optoelectronic emitters. Using first principle density functional (DF) approach, we study the electronic and optical properties of newly synthesized Ba2BiSbO6. Within generalized gradient approximation without SOC, an indirect band gap of 1.85 eV was observed which reduces to 1.72 eV when SOC is taken into account. Significant changes due to SOC has been found at Gamma point in the band structure where band splitting of ~1.3 eV has been observed just above the fermi level with possible indication from indirect to direct band gap semiconductor. Strong hybridization between Bi-6p, Sb-5p and O-2p states observed on the electronic density of states. Optical study shows interband electron transition with energy larger than the bandgap of the material. This suggests Ba2BiSbO6 as a candidate material for photodetectors (absorbers). |
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