Bulletin of the American Physical Society
20th Annual Meeting of the APS Northwest Section
Volume 64, Number 9
Thursday–Saturday, May 16–18, 2019; Western Washington University, Bellingham, Washington
Session C2: Condensed Matter I |
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Chair: Armin Rahmani, Western Washington University Room: Viking Union 567 |
Friday, May 17, 2019 1:30PM - 2:00PM |
C2.00001: Time- and Angle-Resolved Photoemission of Quantum Materials Invited Speaker: Fabio Boschini The phase diagram of copper-oxides hosts intertwined phases as disparate as high-temperature superconductivity, charge order and the pseudogap. In the last decade the development of time-resolved techniques has offered a novel perspective for investigating dynamical properties of quantum phases. In this regard, we recently demonstrated that time-resolved photoemission spectroscopy can disentangle the dynamics of phase fluctuations and charge excitation, establishing the dominant role of phase coherence in the emergence of high-temperature superconductivity in Bi-based cuprates [1]. We employed this same dynamical approach to reveal unambiguously the relation of the pseudogap and short-range antiferromagnetic correlations in optimally-doped NCCO electron-doped cuprate [2], providing clear evidence of the role of short-range correlations in defining the Fermi surface topology. Finally, I will propose a way to redefine the paradigms of the TR-APRES analysis accessing the mode-projected electron-phonon matrix element in graphite in an ultrafast fashion [3]. \\ \\In Collaboration With: Marta Zonno, MengXing Na, Elia Razzoli, Ryan P. Day, Matteo Michiardi, Sergey Zhdanovich, Arthur K. Mills, Giorgio Levy, David J. Jones, Andrea Damascelli; University of British Columbia - Quantum Matter Institute, Eduardo H. da Silva Neto; UC Davis, Claudio Giannetti; Universita Cattolica, Brescia [1] Boschini et al., Nat. Mat. 17, 416 (2018) [2] Boschini*, Zonno* et al., arXiv:1812.07583 (2018) [3] Na*, Mills*, Boschini et al., arXiv:1902.05572 (2019) [Preview Abstract] |
Friday, May 17, 2019 2:00PM - 2:12PM |
C2.00002: Two Leg Ladder of Interacting Majorana Fermions Ethan Cohen, Armin Rahmani Majorana fermions possess a multitude of fascinating qualities. They are their own antiparticle and obey non-abelian exchange statistics, which places them at the forefront of topological quantum computing research. The phases of matter emerging from interacting Majorana fermions are also of considerable interest because the Majorana fermions are the real counterparts of interacting complex electrons. A phase diagram specific to the interacting Majorana fermion system is necessary for understanding their low energy behavior. In this talk, we analyze a two-leg ladder of Majorana fermions and calculate energy gaps and entanglement entropy using the density matrix renormalization group method. [Preview Abstract] |
Friday, May 17, 2019 2:12PM - 2:24PM |
C2.00003: Adsorption of Naptho-Spiropyran On A Graphene Substrate Lucas Browning, Andreas Riemann Spiropyran~is a photochromic molecule that has been studied extensively for its applications in high density optical storage, optical switching, image processing and display.~Spiropyran~is a three-dimensional molecular switch which can be converted to Merocyanine, a planar~isomer~of~Spiropyran~where the central C-O bond has been broken.~ We are specifically studying the two isomers~Naphtho-spiropyran~and~Naphtho-merocyanine adsorbed on a graphene substrate using computational chemistry methods~with a combination of DFT and molecular mechanics. DFT is used to find the charge distribution and configuration while molecular mechanics is used to find the binding energy and adsorption geometry.~ With computational chemistry methods we found adsorption energies and inter-molecular adsorption geometries for the~Spiropyran~molecule on graphite. A similar approach is carried out for~various~Merocyanine isomers.~ [Preview Abstract] |
Friday, May 17, 2019 2:24PM - 2:36PM |
C2.00004: Thermal Expansion of Single-Crystalline H$_2$O and D$_2$O Ice John J. Neumeier, David T. W. Buckingham, Yi-Kuo Yu Thermal expansion of single-crystalline H$_2$O and D$_2$O ice I$h$ with relative resolution of one part in one billion is reported. The measurements were conducted using a thermal expansion cell constructed entirely from fused silica (amorphous quartz), which has an extremely small thermal expansion coefficient. Single crystals were grown using a zone-refining method in a chest freezer purchased from Costco. The crystal growth and measurement methods will be discussed. The measurements reveal a large transition in the thermal expansion coefficient at 101~K in H$_2$O, which moves to 125~K in D$_2$O. It is one of the largest-known isotope effects. Rotational oscillatory modes that couple poorly to phonons appear to be responsible. These types of vibrations are classical in nature, and often called lattice solitons or "intrinsic localized modes". [Preview Abstract] |
Friday, May 17, 2019 2:36PM - 2:48PM |
C2.00005: The optical signatures of amorphous TiO$_{\mathrm{2}}$ thin films Patrick Berry, Okan Agirseven, James Haggerty, David Rivella, Ryan Lance, Janet Tate Reflection and transmission spectra of amorphous thin films of TiO$_{\mathrm{2}}$ reveal significant differences that are related to the oxygen pressure during sputter deposition. The onset of strong absorption, which is related to the semiconductor band gap, is at lower energy in amorphous films deposited at lower oxygen partial pressure than for films deposited at higher oxygen partial pressure. In addition, the lower pO$_{\mathrm{2}}$ films have significantly stronger absorption in the near infrared, which may be caused by free-carrier absorption. Upon rapid annealing at 400ûC, these amorphous films crystallize into one of three polymorphs of TiO$_{\mathrm{2}}$, rutile, brookite, and anatase, and the resulting polymorph is strongly correlated with the oxygen deposition pressure. The signature of the strong absorption onset is retained in the crystalline films. The low-energy absorption decreases in all films as the oxygen content increases upon annealing, but rutile remains slightly absorptive, while absorption disappears in anatase. Optical absorption spectroscopy is therefore a viable means of distinguishing amorphous precursor films from one another and for predicting the crystalline polymorph that results from annealing. [Preview Abstract] |
Friday, May 17, 2019 2:48PM - 3:00PM |
C2.00006: Simulating Strongly Correlated Fermions and Spins with an Optimally Controlled Superconducting Device Matthew Scoggins, Armin Rahmani Numerical solutions to complex many-body models are severely limited by classical computational power. Using controllable quantum devices may help with the simulation of these models. One approach, known as the variational quantum algorithm, is based on tailoring evolution to prepare the a priori unknown ground states of model Hamiltonians. In this work, we address the challenge of finding patterns in optimal variational protocols, where an optimal protocol minimizes the total time it takes to get from the ground state of one device to the ground state of another target device. Using a classical computer, we simulate the evolution of superconducting `gmon' qubits and use Monte-Carlo (MC) simulations to find this optimal protocol for finite systems sizes. The MC method finds optimal protocols that are roughly bang-bang, as predicted by theory. We compare the MC method with an adiabatic method and show that it reaches the ground state in shorter times. Further research will identify patterns in these protocols that can be extrapolated to larger system sizes in order to inform efficient large-scale simulations on the quantum device. [Preview Abstract] |
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