Bulletin of the American Physical Society
Mid-Atlantic Section 2022 Meeting
Volume 67, Number 20
Friday–Sunday, December 2–4, 2022; University Park, PA, Pennsylvania State University
Session C02: Quantum Materials and Nanostructures I |
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Chair: Wilson Yanez, Pennsylvania State University Room: Pennsylvania State University Osmond 104 |
Saturday, December 3, 2022 9:00AM - 9:35AM |
C02.00001: Conserved quantities from entanglement, and timelike entanglement entropy Invited Speaker: Biao Lian In the first part, we show that the subregion entanglement Hamiltonians of excited eigenstates of a many-body system are linear combinations of subregionally (quasi)local approximate conserved quantities, which can be obtained by diagonalizing an entanglement Hamiltonian superdensity matrix (EHSM). For free fermions, EHSM gives a finite number of conserved quantities. In the second part, we generalize the entanglement entropy to timelike subregions, and give the formula for free fermions. For 1D lattice free fermions, the zero-temperature entanglement entropy in a discrete set of times in a time-direction interval stabilizes to the Cardy formula of chiral fermions when the time separation is below a critical value t0, and t0 is given by 2pi divided by the fermion bandwidth. We conjecture the time t0 is an upper bound for consecutive local observations to retrieve information from a quantum state. |
Saturday, December 3, 2022 9:35AM - 10:10AM |
C02.00002: Dirac Theory of Higher-Order Topology Invited Speaker: Bitan Roy The higher-order topological phases manifest a refined bulk-boundary correspondence ensuring gapless modes residing on lower-dimensional boundaries, such as corners and hinges, that remains operative across all the members of the topological family, namely insulators, superconductors and semimetals. In this talk, I will show that a hierarchy of topological phases can be constructed by combining crystallographic symmetry with the abstract mathematical representation theory of anticommuting Dirac matrices. Namely, an nth order topological phase with n>1 can be realized from its conventional or first-order counterpart (n=1) in the presence of n-number of suitable discrete symmetry breaking Wilson-Dirac masses. The resulting higher-order topological phase then supports gapless modes on boundaries, characterized by the codimension n. I will then pedagogically demonstrate its jurisdiction on a large variety of systems realized on a wide variety of material platforms. In particular, I will discuss a systematic construction of higher-order topological insulators, superconductors, Dirac and Weyl semimetals on regular crystals, amorphous networks, self-similar fractal lattices as well as periodically driven Floquet materials. The stability of higher-order topological phases against random charge impurities that are inevitably present in quantum materials will be briefly discussed as well. I will close this talk by pointing out the novel role of bulk crystal defects, such as dislocations and grain boundaries, as the smoking gun probe of higher-order topology. |
Saturday, December 3, 2022 10:10AM - 10:22AM |
C02.00003: Structural ground state exploration of Lennard-Jones-Gauss clusters from genetic algorithms. Nathaniel Wesnak, Soumya Bhat, Aldo H Romero Generally, structures described by pair potentials tend to be compact and isotropic, as in the case of the Lennard-Jones potential. However, introducing a term that produces competing length scales within the interatomic potential can lead to structures with alternative characteristics. This paper searches for and analyzes the low-energy structures for the Lennard-Jones-Gauss double well potential, a classical force-field that is relatively accurate for transition metals. In some areas of the explored parameter space, we find compact atomic structures similar to those found in the Lennard-Jones potential, however we also find regions where the low energy structure is caged or possesses a nontrivial, anisotropic point symmetry group. Metallic clusters with these characteristics possess good catalytic and optical properties, and could also be used to form quasicrystals. We explore the parameter phase space for the lowest energy structures for atomic clusters with 20 to 70 atoms within a selected range of the two parameters describing the potential. We also report some results with a finer parameter grid exploration for the region in which more diverse structures are found. For this, we report results for sizes of structures between 20 to 50 atoms. Cluster stability is also explored by investigating the appearance of imaginary vibrational modes on the low energy configurations, which can give information on if the structure can realistically exist. Parameter regions where caged structures correspond to the lowest energy configurations can be of great interest for materials and supra-chemistry design. |
Saturday, December 3, 2022 10:22AM - 10:46AM |
C02.00004: Charge to spin conversion in the Weyl semimetal NbAs Wilson J Yanez, Yongxi Ou, Yu-Sheng Huang, Supriya Ghosh, Emma K Steinebronn, Andre Mkhoyan, Nitin Samarth
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Saturday, December 3, 2022 10:46AM - 10:58AM |
C02.00005: Green synthesis of various nanoparticle species using spent coffee grounds Brian Yust, Niny Rao, Evan Schwarzmann Nanotechnology and nanoparticles (NPs) have become a common part of our modern society with uses ranging from medicine and biotechnology to cosmetics, synthetic lubricants, and food safety products. Among these technologies, one emerging NP synthesis method is to utilize food waste products, such as spent coffee grounds (SCGs), adding value and a secondary use for materials which would otherwise have been discarded. SCG synthesis is considered a green synthesis technique which avoids unnecessary exposure to toxic chemicals and reduces harmful waste by replacing caustic precursors with food-derived active compounds. This is in contrast to the many other bottom-up synthesis methods including traditional wet-chemical synthesis, thermal decomposition, hydrothermal, sol-gel, and microemulsion, that utilize hazardous or toxic chemicals and often also produce hazardous or toxic chemical waste. Further, after these syntheses, chemical residues may remain on the surface of these NPs which can affect their biocompatibility, water solubility, end-use function or other attributes. Thus in this study, we seek to expand the understanding and applicability of SCG syntheses of various NP species using SCG extract as the reducing, nucleating, or capping agent in a wet-chemical synthesis. We analyze the impacts of SCGs acquired by hot brew, cold brew, and espresso techniques. Of particular interest are the total antioxidant activity and total caffeoylquinic acid of extracts obtained from SCGs as they play a major role in reduction and nucleation of metal ions during synthesis. Potential new avenues for NP synthesis will also be discussed. |
Saturday, December 3, 2022 10:58AM - 11:10AM |
C02.00006: Exploring the universal nucleation behaviour and anomalies in sheared supercooled liquids Amrita Goswami One of the most ubiquitous and technologically important phenomena in nature is the nucleation of homogeneous flowing systems. Homogeneous nucleation is notoriously challenging to study using computational methods, since it is usually a stochastic rare event according to the spatio-temporal resolution of molecular dynamics (MD) simulations. Imposing a constant shear rate, which is a non-equilibrium effect, adds to the complexity of the problem. |
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