Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session E40: Properties of Bilayer Graphene |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Jing Li, Pennsylvania State Univ Room: LACC 501C |
Tuesday, March 6, 2018 8:00AM - 8:12AM |
E40.00001: Helical Network Model of the Twisted Graphene Bilayer Dmitry Efimkin, Allan MacDonald
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Tuesday, March 6, 2018 8:12AM - 8:24AM |
E40.00002: Quantum Transport in Gapped Bilayer Graphene in the Presence of Long-Range Disorder Christopher Hipp, Jens Bardarson, Enrico Rossi In this work, we study the electron transport of gapped bilayer graphene in the presence of the long-range disorder due to charge impurities. For each disorder realization we obtain the spatial carrier density profile of the ground state using a generalization of the Thomas-Fermi theory and then the conductance via a fully quantum mechanical approach. By considering several disorder realizations we obtain disorder-averaged results. We find that the disorder-induced carrier density inhomogeneties strongly affect the nature of the electronic transport. In addition, we find that the quantum mechanical treatment of the scattering problem leads to results that in some cases are qualitatively different from the results obtained via a semiclassical approach. |
Tuesday, March 6, 2018 8:24AM - 8:36AM |
E40.00003: Andreev reflection in bilayer graphene: Crossover from retro-reflection to specular reflection Abhiram Soori, Manas Sahu, Anindya Das, Subroto Mukerjee Andreev reflection in graphene is special since it can be of two types- retro or specular. Bilayer graphene (BLG) is a better candidate to observe the crossover from retro to specular since charge density fluctuations across the sample are much lower. We propose a scheme to observe the features of specular Andreev reflection in normal metal (NM)-superconductor (SC) junction on BLG more clearly. Our scheme involves applying a magnetic field to the NM side of the NM-SC junction on BLG. We calculate conductance as a function of chemical potential and bias within the superconducting gap. From the conductance spectrum, we identify the regions of specular- and retro- type Andreev reflection. |
Tuesday, March 6, 2018 8:36AM - 8:48AM |
E40.00004: Interlayer exciton spectral dynamics and photoemission in twisted bilayer graphene Hiral Patel, Kyle Vogt, Lujie Huang, Jiwoong Park, Matt Graham Upon resonant two-photon excitation of twisted bilayer graphene (tBLG), we observe weak light emission that is spectrally tunable with the stacking angle. This signal is best ascribed to photoluminescence from thermalized bright and dark strongly-bound interlayer exciton states. The spectral fine-structure and long-lived exciton kinetics are further obtained from individual tBLG domains through two-photon photoluminescence excitation spectra and intraband transient absorption spectra on single tBLG grains. Spectral peaks in both two-photon photoluminescence and transient spectrum of intraband exciton transition independently quantify show the interlayer exciton states have binding energies ranging from ~0.4-0.75 eV, as a function of the stacking angle from 8o to 17o. This suggests that photoluminescence collected from the tBLG domain is enabled by the quasi-stable interlayer excitons that coexist alongside graphene continuum states. Theoretical simulations suggest this stable coexistence results from a vanishing exciton-continuum coupling strength resulting from the rehybridization of two degenerate van-Hove singularity-like transitions predicted in the tight-binding model for tBLG. |
Tuesday, March 6, 2018 8:48AM - 9:00AM |
E40.00005: ABSTRACT WITHDRAWN
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Tuesday, March 6, 2018 9:00AM - 9:12AM |
E40.00006: Plasmonic Effects in Twisted Bilayer Graphene Sai Sunku, GuangXin Ni, Bor-Yuan Jiang, Hyobin Yoo, Alexander McLeod, Aaron Sternbach, Philip Kim, Michael Fogler, Dimitri Basov Twisted bilayer graphene, consisting of two monolayer graphene sheets rotated relative to each other, has a unique electronic band structure distinguished by the appearance of van Hove singularities and sensitive dependence on the twist angle. When compared to bernal-stacked bilayer graphene, the presence of van Hove singularities is expected to strongly modify the dispersion of surface plasmon polaritons leading to additional damping pathways and collective excitonic modes called interband plasmons. In this work, we use scattering scanning near-field optical microscopy to launch and image surface plasmon polaritons and shed new light on twisted bilayer graphene. |
Tuesday, March 6, 2018 9:12AM - 9:24AM |
E40.00007: Designer bandstructures in bilayer graphene by superlattice patterning Yutao Li, Carlos Forsythe, Cory Dean With a locally tunable band gap on the order of 100meV, bilayer graphene is a simple yet promising 2D material with various potential applications in nanoelectronics. The electronic structure of bilayer graphene can be engineered by a superlattice, producing novel effects including Brilliouin zone folding, additional Dirac fermions and Hofstader’s butterfly. Here we present our magneto-transport data from bilayer graphene devices with electrostatically-defined superlattices whose wavelength can be as small as 35nm. In addition, we compare these data with our previous data on monolayer graphene superlattices and predictions from various theoretical models. Based on these results, we also discuss the feasibility of creating graphene antidot lattices using bilayer graphene dielectric superlattices. Previous theoretical studies have shown that such lattices are capable of inducing localized electronic states with a long spin-coherence time and therefore a candidate for carbon-based qubits for quantum computing. |
Tuesday, March 6, 2018 9:24AM - 9:36AM |
E40.00008: One Dimensional Modulation of Electronic States in Bilayer Graphene Siqi Wang, Mervin Zhao, King Yan Fong, Yuan Wang, Xiang Zhang Recent advances in van der Waals assemblies have enabled high quality and performance of two-dimensional materials devices, demonstrating emergent condensed matter phenomena. The electronic states of these materials can be manipulated by imposing artificially designed potentials through an external electric field. We fabricated a one-dimensional periodic top-gate on h-BN encapsulated bilayer graphene by state-of-the-art electron beam lithography. Through combination of the grating-like top-gate potential and local graphite back-gate, the imposed electric potential strength can be well controlled and modulate the electronic properties of bilayer graphene. We observed signatures of superlattice modulation on both the first and secondary charge neutral points in the longitudinal resistance measurement at zero magnetic field. The change of modulation pattern with weak magnetic field is also studied. Our modulated bilayer graphene may hold promise for the realization of electron distributed Bragg reflector (DBR) in the future application of electron optics. |
Tuesday, March 6, 2018 9:36AM - 9:48AM |
E40.00009: Valley-symmetric quantized conductance in bilayer graphene constrictions Hyunwoo Lee, Geon-Hyoung Park, Kenji Watanabe, Takashi Taniguchi, Hu-Jong Lee Electrical transport across top-gated short constrictions of bilayer graphene is investigated. Realizing a quasi-one-dimensional (quasi-1D) channel along a physically tailored graphene layer turns out to be extremely challenging due to scattering by the edge disorder and charged puddles. In this study, to obtain the ballistic quasi-1D channel by minimizing the edge scattering in bilayer graphene, we prepared short constrictions of bilayer graphene encapsulated between a pair of crystalline hexagonal boron nitride (hBN) flakes. At high charge carrier densities, lateral confinement of charge carriers in the short constriction (~200 nm wide and ~50 nm long) of hBN-encapsulated bilayer graphene leads to the formation of quasi-1D channels, showing the quantized conductance in steps of ~4e2/h for varying the Fermi wavelength. This signifies that both spin and valley degeneracies are preserved for the carrier transport through the short constriction. We study the evolution of quantized conductance with varying parameters such as magnetic field, temperature, and bias voltage. |
Tuesday, March 6, 2018 9:48AM - 10:00AM |
E40.00010: Strain engineering of bilayer graphene with spatially corrugated domain Sheng-Chin Ho, Yu-Chiang Heish, Thi Hai Yen Vu, Shun-Tsung Lo, Tse-Ming Chen Nanostructural engineering pave an crucial routes to realize artificial band structures, superlattices and spectrum [1,2,3]. Graphene, which is one of the most attractive materials, can be spatially deformed to induce a strain gauge field, which opens a novel topic named “straintronics” [4]. Here, we develop a method to locally engineer the bilayer graphene in a corrugated pattern such that we can simultaneously investigate and compare the flat and corrugated regions in the same bilayer graphene device. Unconventional negative magnetoresistance (MR) is observed in corrugated region when an in-plane magnetic field is applied. Such negative MR is further studied as a function of temperature and carrier density. |
Tuesday, March 6, 2018 10:00AM - 10:12AM |
E40.00011: Excitations of the ν = 0 state of bilayer graphene Jing Li, Zhenxi Yin, Jun Zhu The filling factor n = 0 state of bilayer graphene (BLG) exhibits a rich phase diagram driven by a displacement field D, a perpendicular magnetic field Bperp and an in-plane magnetic field Bip. In a small Bperp and in the vicinity of D = 0, experiments show that an increasing Bip drives the BLG from an insulating, presumably canted anti-ferromagnet (CAF) phase to a quantum spin Hall (QSH) phase, which is ferromagnetic in the bulk and carries metallic edge states. Systematic experimental studies of these interesting phases, however, are lacking. In high-quality, dual h-BN encapsulated and gated BLG devices, we have performed temperature-dependent conductance measurements G (T) of the CAF and the QSH states in tilted B-field up to 31T. G (T) of the CAF state continuously decreases as a function of T without an apparent activation gap. G (T) of the QSH state is non-monotonic in the range of 0.3 K < T < 50 K, where dG/dT changes sign a few times. Even at the lowest temperatures, dG/dT does not exhibit a universal sign among the several devices we measured although all exhibit G ~ 4e2/h. We discuss possible mechanisms including the dynamics of the metallic edge states and the conduction and excitations of the bulk ferromagnet. |
Tuesday, March 6, 2018 10:12AM - 10:24AM |
E40.00012: Anomalous drag and charge density order in Double Bilayer Graphene Jia Li, Takashi Taniguchi, Kenji Watanabe, James Hone, Cory Dean
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Tuesday, March 6, 2018 10:24AM - 10:36AM |
E40.00013: Electrical transport at bilayer graphene domain wall Lili Jiang, Sheng Wang, Chenhao Jin, Feng Wang Layer-stacking domain wall in bilayer graphene strongly alters its electronic properties and gives rise to fascinating new physics such as quantum valley Hall edge states. In our previous works, we demonstrated that the domain wall can be visualized by near-field infrared microscopy and we can control their movement with an AFM tip. To get a comprehensive understanding of such topological defect, we study the electrical transport at bilayer graphene domain wall in this work. |
Tuesday, March 6, 2018 10:36AM - 10:48AM |
E40.00014: Marginally self-averaging one-dimensional localization in bilayer graphene Aamir Mohammed Ali, Paritosh Karnatak, T. Phanindra Sai, T. V. Ramakrishnan, Rajdeep Sensarma, Arindam Ghosh In a disordered system, a macroscopic variable X is spatially ergodic, or self-averaging, when its relative fluctuations RX =〈(ΔX)2〉/〈X2〉 → 0 as L → ∞, where L is a linear dimension and 〈...〉 represents averaging over different realizations of disorder. For strongly localized noninteracting carriers the electrical conductance g does not self-average, but its logarithm ln g does, in a manner that is determined by the dimensionality and the scaling properties of Anderson localization for L » ξ, the localization length. In this work, we show that in the strongly insulating bilayer graphene (BLG), the relative fluctuations in ln g with chemical potential decay nearly logarithmically for channel length up to L ≈ 20ξ. This 'marginal' self-averaging along with its associated dependence of 〈ln g〉 on L, suggest that transport in strongly gapped BLG takes place via strictly one-dimensional channels, with the ξ ≈ 0.5 ± 0.1 μm much longer than that expected from the bulk bandgap. Our experiment not only reveals a nontrivial localization mechanism in BLG based on robust edge modes, but is also the first demonstration of the marginal self-averaging nature of strong localization in one dimension. |
Tuesday, March 6, 2018 10:48AM - 11:00AM |
E40.00015: In-Plane Thermal Conductivity of Misoriented Bilayer Graphene Chenyang Li, Bishwajit Debnath, Shanshan Su, Roger Lake Misorientation of two layers of bilayer graphene leaves distinct signatures in the electronic properties and the phonon modes. The effect on the thermal conductivity has received the least attention and is the least well understood. In this work, the in-plane thermal conductivity of misoriented bilayer graphene is simulated as a function of temperature and interlayer rotation angle using both density functional theory (DFT) and nonequilibrium molecular dynamics (NEMD). Both calculations give the same qualitative dependencies of the thermal conductivity on the rotation angle. Misorientation reduces the in-plane thermal conductivity at room temperature. As the temperature increases, the in-plane thermal conductivity difference between AB-BLG and misoriented bilayer graphene (m-BLG) becomes less significant. The trends are consistent with the existing experimental data.1 |
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