Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session EE07: V: Complex Structured Materials, Including Graphene I |
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Sponsoring Units: DCMP Chair: Joshuah Heath, Dartmouth College Room: Virtual Room 7 |
Monday, March 20, 2023 10:00AM - 10:12AM |
EE07.00001: A computational study of the impact of voids on the percolation electronic conductivity of nanowire networks Guoting Cheng, Prithviraj Pachal, Devendra K Gorle, Ant Ural Understanding the impact of voids, which could be present due to the deposition process or introduced intentionally, on the electronic properties of nanowire networks is critical for applications such as transparent conductive electrodes, thin film transistors, sensing, and hardware security. Employing Monte Carlo simulations, we first compute the percolation probability in these networks as a function of nanowire density for different void sizes. Assuming a Gaussian percolation probability density function, we find that both the mean and standard deviation increase with increasing void size. We then compute the relative conductivity change as a function of nanowire density for different void sizes and find that it increases as the square root of the void area. We also study the effect of the location and aspect ratio of the void, the finite size of the network, and the junction to nanowire resistance ratio on the percolation probability and relative conductivity change of the nanowire network. Furthermore, we generate curvy nanowires using third order Bezier curves characterized by the curviness angle and aligned nanowires using an orientation characterized by the alignment angle. We then investigate the impact of voids on networks consisting of curvy and aligned nanowires. These computational results demonstrate the significant impact voids have on the electronic properties of two-dimensional networks consisting of one-dimensional nanowires. |
Monday, March 20, 2023 10:12AM - 10:24AM |
EE07.00002: Giant Polarizing Effect from Strongly Absorptive 20-nm Nano-wires: Absorptive Nano-wire Polarizers Lisa R Wang, Yifei Jin, Yifei Jin Large area (200-mm in diameter) 20-nm wide and 200-nm tall nano-wire arrays with 50-nm spacing made of strongly absorptive materials such as titanium dioxide or platinum generate a giant polarizing effect in the deep ultraviolet (DUV) wavelength band. The polarizing effect results from anisotropic absorption created by the nano-wire structure. Different from highly conductive metallic nano-wire polarizers resulting from anisotropic conduction, the absorptive nano-wire polarizers create a new category of polarizing devices that can handle extremely high temperature and high-intensity ultraviolet exposure. The innovative DUV polarizers make many important applications possible. |
Monday, March 20, 2023 10:24AM - 10:36AM |
EE07.00003: Nanoscale Mapping of Resistivity and Charge Trap Activities in Carbon Nanotube-based Nanostructures Yuhyeon Oh, Narae Shin, Jeongsu Kim, Shashank Shekhar, Myungjae Yang, Seunghun Hong We report a method for the nanoscale mapping of resistivity and charge trap activities in carbon nanotube (CNT)-based nanostructured films such as metallic single walled carbon nanotube (m-SWCNT) networks embedded in gold thin films. In this method, a conducting probe made a direct contact with CNT-based nanostructured films, and it was utilized to measure the maps of electrical currents and noises. The measured maps were analyzed to estimate the nanoscale variation of resistivity (ρ) and the density distribution of charge traps (Neff). For example, a hybrid film composed of m-SWCNT networks and gold films exhibited 300% improved conductivity and significantly reduced charge trap densities compared to that of pristine gold films. Interestingly, we found that the ρ and Neff on both CNT/gold and pristine gold regions exhibited a scaling behavior like ρ ∝ Neff0.5, indicating hopping charge conductions and noise characteristics of the hybrid films. Since our method allows one to map the resistivity and charge trap activities with a nanoscale resolution, it can be a powerful tool for a basic study of nanoscale charge transport phenomena and a practical application based on nanostructured channels. |
Monday, March 20, 2023 10:36AM - 10:48AM |
EE07.00004: Flat bands through electrically tunable superlattice in Bernal stacked bilayer graphene Xu Du, Jiacheng Sun, Fernando E Camino In 2-dimensional (2d) crystals, imposing nanometer-scale periodicity allows tuning the fundamental Bloch electron spectrum, enabling novel physics properties which are not accessible in the original crystal. A celebrated example is the Moire heterostructures where wide variety of exotic charge transport phenomena emerges. In recently years, a top-down approach for creating 2d superlattice on monolayer graphene by meaning of nanopatterning of electric gate has been studied, allowing formation of custom-design superlattice potential and study of band structure engineering. With this approach, however, electron correlation which leads to many forefront physics problems, remains to be undiscovered. Here we discuss our work on Bernal-stacked bilayer graphene modulated by gate-defined superlattice potential. We observed strong evidence of formation flat band stacks which potentially host correlated electrons. We will also discuss possible signatures of correlated insulator in these systems. The possibility to induce correlated electrons with nanopatterning defined electric gates paves the path to custom-design superlattices with arbitrary geometries and symmetries, for studying band structure engineering and strongly correlated electrons in 2d materials. |
Monday, March 20, 2023 10:48AM - 11:00AM Author not Attending |
EE07.00005: Simulation of the Cyclotron Resonance in Dual-Gated Bilayer Graphene phase diagram Matheus O Schossler, Jordan Russell, Yafis Barlas, Alexander Seidel, Erik Henriksen We present numerical simulations of the cyclotron transitions between Landau-levels (LL) in dual-gated bilayer graphene and its dependence on the external electric potential (U) at magnetic field B = 13 T. This dual gate device allows independent control over density ($ u$) and electric potential (U). Taking into account Coulomb interactions in Hartree-Fock approximation, anisotropic terms, including electron-phonon interactions, and regularization effects from the infinitely deep Fermi sea, we capture a phase transition from a canted anti-ferromagnetic phase (CAF) into a fully polarized phase (FLP) at the charge neutrality point and a critical U matching with recent experimental measurements. At neutrality, the transitions from LL -2 →1 and LL 1 → 2 are found to be in agreement with experiments at high U. At $ u=4$, when all eight states with LL indices 0 and 1 as well as both spin and valley orientations are filled, the theory fits experimental results with high precision. |
Monday, March 20, 2023 11:00AM - 11:12AM |
EE07.00006: Double and Quadruple Flat Bands tuned by Alternative magnetic Fluxes in Twisted Bilayer Graphene Congcong Le, Qiang Zhang, Fan Cui, Xianxin Wu, Ching-Kai Chiu Twisted bilayer graphene (TBG) can host the moire energy flat bands with two-fold degeneracy serving as a fruitful playground for strong correlations and topological phases. However, the number of degeneracy is not limited to two. Introducing a spatially alternative magnetic field, we report that the induced magnetic phase becomes an additional controllable parameter and leads to the emergence of four-fold degenerate flat bands. This emergence stems from the band inversion at $Gamma$ near the Fermi level as both the twisted angle and the magnetic phase vary. Using holomorphic functions, which explain the origin of the double flat bands in the conventional TBG, we can generate analytical wave functions in the magnetic TBG to show absolutely flat bands with four-fold degeneracy. In contrast, the conventional TBG has only two moire energy flat bands, and the highly degenerate flat bands in this magnetic platform might bring richer correlation physics |
Monday, March 20, 2023 11:12AM - 11:24AM |
EE07.00007: Moiré phonons and electron-phonon couplings in magic-angle twisted bilayer graphene Bo Xie, Bo Xie, Xiaoqian Liu, Ran Peng, Zhaoru sun, Jianpeng Liu In this work, we study the moiré phonon properties and electron-phonon couplings in magic-angle twisted bilayer graphene based on both ab initio deep potential molecular dynamics (DPMD) and an effective continuum model approach. We calculate the phonon dispersions and analyze the moiré phonon vibrational modes at high-symmetry points in the moiré Brillouin zone. Both of our methods predict the presence of low-frequency optical soft modes at Γ point exhibiting dipolar, quadrupolar, and octupolar-type out-of-plane vibrations. Additionally, the in-plane “phason” (or “sliding”) modes that were gapless calculated from the continuum-model approach turn out to be gapped from the DPMD calculations, which are due to the lattice commensuration effects. We also study effects of electron-phonon couplings, and find that some of the frozen soft moiré phonon may lead to peculiar charge order and gapped Dirac states. |
Monday, March 20, 2023 11:24AM - 11:36AM |
EE07.00008: Self-Similar and Neuromorphic Properties in Core-Shell Nanowire Network Systems Elijah Adams, Claudia Gomes da Rocha Human brains process sensory signals better than any modern computer, which is why we are investigating synthetic circuit networks that mimic neurobiological behavior. Our networks are composed of randomly distributed core-shell nanowires through which electrical signals can propagate. Current flows through their wire cores and can be transmitted from wire to wire through junctions. The junctions offer resistance to the passage of current, but they do not behave as static resistors; they exhibit an adaptable resistance memory (memristance) that can be used to emulate neuron synapses in nanowire networks (NWNs). |
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