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 S20: Graphene Electronic Phenomena |
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Sponsoring Units: DCMP Chair: Mu Wang Room: Room 212 |
Thursday, March 9, 2023 8:00AM - 8:12AM |
S20.00001: Controllably Straining Graphene Ribbons via Electrostatic In-Plane Actuation Megan Eisele, Maëlle A Kapfer, Bjarke S Jessen, Nathan R Finney, Cory R Dean Bending monolayer ribbons of two-dimensional materials in-plane has previously demonstrated moiré patterns with highly tunable wavelengths and low disorder. Previously, in-plane bending was achieved by pushing monolayer ribbons with an atomic force microscope (AFM) tip, with samples showing uniform twist angle variations and strain gradients. The AFM bending method, however, does not allow for dynamic control of ribbon deflection, which follows a simple cantilever bending model. Actuation of graphene ribbons on an hBN substrate via an in-plane electrostatic force provides a comparable bending mechanism to mechanical manipulation but has the added benefit of in-situ control over the graphene deflection. Electrostatic actuation of the graphene further expands the range of twist angles and strain values that can be achieved with a single device. Additionally, this demonstration of graphene actuation on hBN is promising for the creation of highly programmable devices and paves the way for the development of novel, 2D materials-based MEMS. |
Thursday, March 9, 2023 8:12AM - 8:24AM |
S20.00002: Topological Domain Walls in Graphene Nanoribbons with Carrier Doping Takuto Kawakami, Gen Tamaki, Mikito Koshino We present a theory for the magnetic ground states in doped zigzag graphene nanoribbons (ZGNRs) and clarify the topological origin of their domain wall structure. It is theoretically known that non-interacting ZGNRs have edge states with flat dispersion relation and the electron-electron interaction induces a magnetic order [1,2]. Here we examine the effect of carrier dope on the magnetic structure in terms of the Hartree-Fock mean-field approach. In the low carrier density regime, we observe that magnetic domains with alternating magnetic order is spontaneously formed consistently with Ref. [3]. We analytically demonstrate that the domain-wall bound states are topologically protected by the winding number defined in an effective continuum model. In increasing the doped carrier densities, the distance between the periodically aligned domain walls becomes smaller, and magnetic domain structure crosses over to the spin and charge density wave. We also find that the electronic spectrum as a function of carrier density exhibits a fractal pattern like the Hofstadter butterfly, due to competition of the periodic magnetic structure and atomic lattice. |
Thursday, March 9, 2023 8:24AM - 8:36AM |
S20.00003: Transport anisotropy of one-dimensional graphene superlattice induced by periodic ferroelectric domains Tianlin Li, Hanying Chen, Kun Wang, Yifei Hao, Le Zhang, Qiuchen Wu, Takashi Taniguchi, Kenji Watanabe, Xia Hong We investigate the transport anisotropy in one-dimensional (1D) graphene superlattice (GSL) induced by prepatterned periodic domains in a ferroelectric bottom gate. We work with 50 nm single crystalline ferroelectric Pb(Zr,Ti)O3 (PZT) films deposited on (La,Sr)MnO3 buffered SrTiO3 substrates. Periodic polarization up (Pup) and down (Pdown) stripe domains are patterned on PZT using conductive atomic force microscopy. The domain periodicity varies from 200 nm to 266 nm. We then transfer hBN-graphene stacks onto the pre-patterned domains and fabricate them into top-gated FET devices. The difference in carrier density between the two polarization regions reaches around 3×1013 cm-2 at 2 K due to the pyroelectric effect. For the 1D GSL with current perpendicular to the stripe domains, the hBN top gate induces extra Dirac points in R(Vg), with the position further splitting in magnetic field. We also investigate how the magnetoresistance and quantum Hall effects of the GSL vary with the current direction with respect to the stripe domain orientation. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S20.00004: Engineering and Probing graphene-based 1D channels Nishat Sultana, Robert W Rienstra, Akhil Chauhan, Takashi Taniguchi, Kenji Watanabe, Nikolai Zhitenev, Joseph A Stroscio, Fereshte Ghahari Interaction effects might play an important role in transport properties of a clean ballistic 1D channel. The study of electronic properties of confined electrons in 1D nanostructures is a less explored area in layered materials research mostly due to technical difficulties related to disorder and lack of control on the confinement potentials. In this talk I will describe techniques to achieve electrostatic control over sub-50nm length scales with contaminant free interfaces thus creating clean and tunable nano constrictions in vdW heterostructures. I will also discuss transport measurements of these narrow channels both at zero and high magnetic fields where the interplay between confinement and interaction effects can lead to novel transport regimes. |
Thursday, March 9, 2023 8:48AM - 9:00AM |
S20.00005: Effects of electron-electron interactions on nontrivial flat bands in graphene nanoribbon networks Gen Tamaki, Yuji Hamamoto, Takuto Kawakami, Yoshitada Morikawa, Mikito Koshino We theoretically study the ground state of graphene nanoribbon networks (GNR networks), which are periodically arranged networks of graphene nanoribbon junctions, when electron-electron interactions are present. The GNR network exhibits a variety of band structures depending on the junction structure, with a two-electron localized junction structure exhibiting an hourglass-shaped band composed of flat bands and graphene-like bands [1]. We have calculated the ground state for this structure using the Hatree-Fock approach. As a result, several ordered structures including spin/charge/orbital ordered states are found in the strong electron-electron interaction regime. Depending on the order structure, the flat band can be dispersed, form a gap, or transform into a tilted Dirac cone. |
Thursday, March 9, 2023 9:00AM - 9:12AM |
S20.00006: Polarization Charge around Impurities in Strained and Tilted 2D Dirac materials Mohamed M Elsayed, Sang Wook Kim, Juan M Vanegas, Valeri N Kotov We demonstrate that uniaxial strain, as well as the cone tilt naturally present in certain 2D Dirac materials, introduces quasiparticle anisotropy that has a profound effect on the polarization charge induced by external impurities (both Coulomb and short-range). For example, the charge distribution induced by a Coulomb impurity exhibits an unconventional power law tail along with a strain-dependent admixture of angular harmonics. Analytical results were obtained in the continuum limit via perturbation theory valid for weak (subcritical) potentials, and supported by numerical lattice simulations based on density-functional theory. The presence of distributed charge is in sharp contrast to the response in pristine graphene, where the polarization charge is fully localized at the impurity position. Thus measurements of the charge response reflecting this novel behavior may be used to extract information about the mechanical and electronic properties of a sample. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S20.00007: Electrical transport in graphene-based systems with tunable Coulomb interaction Xueshi Gao, Xin Li, Kenji Watanabe, Takashi Taniguchi, Xiaoshan Xu, Chun Ning Lau Coulomb interaction is one of the key mechanisms in low-dimensional physics, which gives abundant phase diagrams with broken-symmetry states. Such broken-symmetry states have been reported in SrTiO3 supported monolayer graphene. However, it is yet to be achieved to tune Coulomb interaction continuously in low-dimensional system, and to explore the phase diagram in more complicated systems. Here, we experimentally study graphene-based systems on ferroelectric Y-doped HfO2 substrate. In this talk, I will present our latest discoveries on the electronic properties in graphene systems with tunable Coulomb interaction. |
Thursday, March 9, 2023 9:24AM - 9:36AM Author not Attending |
S20.00008: Electron-Hole Bound State in Graphene Partha Sarathi Banerjee, Rahul Marathe, Sankalpa Ghosh The dispersion for monolayer graphene shows a gap-less spectrum. Such monolayer graphene can be gated by a charged Carbon Nanotube(CNT) placed at a distance from the graphene sheet and create both potential barriers and wells for the charge carriers in monolayer graphene. If two oppositely charged CNTs are placed at some distance, a potential well and a barrier are formed for an electron. In such systems, the barrier for a hole acts as a well for an electron and vice versa. We analytically study the formation of the electron-hole bound state in such systems and their consequences for many-body physics. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S20.00009: Ab initio calculations of low-energy quasiparticle lifetimes in bilayer graphene Catalin D Spataru, Francois Leonard Motivated by recent experimental results [1], we calculate from first-principles the lifetime of low-energy (within 200 meV from the Fermi energy) quasiparticles in bilayer graphene. We take into account the scattering rate arising from electron-electron interactions within the GW-approximation for the electron self-energy and consider several p-type doping levels ranging from 0 to about 3x10^12 holes/cm^2. In the undoped case we find that the average inverse lifetime scales linearly with quasiparticle energy away from the charge neutrality point, with values in good agreement with experiments. In the doped case, the dependence of the inverse lifetime on quasiparticle energy acquires a non-linear component due to the opening of an additional decay channel mediated by acoustic plasmons. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S20.00010: Electron tunneling for Rashba model in graphene over a square potential barrier Paula Fekete, Godfrey Gumbs, Andrii Iurov, Liubov Zhemchuzhna, Danhong Huang, Travis Rogowski, Dipendra Dahal We have calculated the transmission coefficient and the tunneling conductance across a square potential barrier for both graphene and a dice lattice in the presence of linearly polarized off-resonant dressing field. The linearly-polarized, external electromagnetic field induces anisotropy into the energy dispersion of tunneling electrons so that the cross section of a Dirac cone becomes elliptical. The wave vector, the spinor vector, and the group-velocity vector are no longer aligned to each other. The normal direction to a barrier layer in the tunneling system could be misaligned with the major axis of the ellipse, exhibiting an asymmetric Klein paradox for an off-normal-direction tunneling. The resulting tunneling current in this system is calculated by using a transmission coefficient and a longitudinal group velocity for different types of α-T3 materials and misalignment angles. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S20.00011: Topologically-Induced Gapping in Graphene Benjamin Katz, Vincent H Crespi, Paul E Lammert Disclinated sp2 carbon surfaces show a clear pattern in their density of states (DOS) with the separation of these disclinations. This arises from the effect of the topology of the π-bonding network on phase matching around these disclinations, and can produce a striking scaling behavior of the DOS to a level of fine detail within an energy window determined by the areal density of the disclinations. Motivated by the presumed existence of a low-energy continuum description of the system, which should give a scaling of DOS that varies inversely with the separation of disclinations, we look for this scaling and find it exists in families grouped by their separation in distance in the bond network, much like the (n-m) mod 3 rule for carbon nanotubes. These groupings (and their associated spacings mod 3) predict whether a specific structure has a gapped DOS at the Fermi energy, and the size of the gaps in the gapped structures are of the order predicted by a low-energy continuum model description. Notably, this behavior (including the scaling of the DOS) persists down to separations where the disclinations are not significantly distant from each other, and a continuum model would not be anticipated to work well. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S20.00012: Transient Hole Doping in Epitaxial Graphene Albert F Rigosi, Swapnil M Mhatre, Ngoc Thanh Mai Tran, Heather M Hill, Dipanjan Saha, Angela R Hight Walker, Chi-Te Liang, Randolph E Elmquist, David B Newell This work reports the dynamics of transient hole doping in epitaxial graphene devices by using nitric acid as an adsorbent. The timescales associated with corresponding desorption processes are extracted from the data. The understanding of reversible hole doping without gating is of crucial importance to those fabricating devices with a particular functionality. Measurements of the electrical and optical properties of several devices post-exposure were performed with transport temperatures between 300 K and 1.5 K. Ambient conditions are applied to non-transport measurements to replicate the most likely laboratory conditions for handling devices using this doping method. The relevant timescales from transport measurements are compared with results from Raman spectroscopy measurements. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S20.00013: Inhomogenous local electronic structure in overdoped graphene Raymond E Blackwell, Abhay N Pasupathy, Kazuhiro Fujita, Zengyi Du, Asish K Kundu, Ilya K Drozdov, Zebin Wu, Dante M Kennes, Takuya Okugawa Over the last two decades, graphene has emerged as a platform to study a myriad of many-body interactions. For example, upon sufficiently high levels of doping the van Hove singularity (vHS) has been shown to evolve such that it has extended character instead of pointlike character in pristine graphene. Here, we investigate the effects of ytterbium intercalation on the electronic structure in a single layer of graphene using spectroscopic imaging scanning tunneling spectroscopy (SI-STM) and angle-resolved photoemission spectroscopy (ARPES). Our results demonstrate that ytterbium atoms behave as both chemical and substitutional dopants. Moreover, while the global electronic structure characterized via ARPES appears to be homogenous, SI-STM reveals substantial inhomogeneity in the local electronic structure. In particular, the energies of the vHS and Dirac cone vary considerably as a function of position. Our results suggest that the band structure of graphene undergoes significant renormalization caused by the ytterbium dopants. |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S20.00014: Desorption timescales on epitaxial graphene via Fermi level shifting and Reststrahlen monitoring Albert F Rigosi, Swapnil M Mhatre, Ngoc Thanh Mai Tran, Cristiane N Santos, Adam Biacchi, Mathew L Kelley, Heather M Hill, Dipanjan Saha, Chi-Te Liang, Randolph E Elmquist, David B Newell, Benoit Hackens, Christina A Hacker We report experimental results related to the transience of hole doping in epitaxial graphene-based devices when nitric acid is used as an adsorbent. The desorption processes are monitored under vacuum conditions by electrical and spectroscopic means to extract the relevant timescales from the corresponding data. The measurements are mostly performed at room temperature, with some electrical transport data collected at 1.5 K. The relevant timescales from transport measurements are compared with the results obtained from X-ray photoelecton spectroscopy and Fourier transform infrared spectroscopy measurements, with the latter performed at ambient conditions and accompanied by calculations of the spectra in the Reststrahlen band. This approach can elucidate the reversible nature of hole doping while also providing a suitable alternative for large-scale device doping that need not rely on standard metallic gating. |
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