Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L54: 2D Heterostructures -- TransportFocus
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Sponsoring Units: DCMP Chair: Jianhao Chen, Peking University Room: BCEC 254A |
Wednesday, March 6, 2019 11:15AM - 11:27AM |
L54.00001: Perfectly gate-tunable graphene-WSe2 van der Waal’s heterostructure at the Schottky-Mott limit Samuel LaGasse, Prathamesh Dhakras, Takashi Taniguchi, Kenji Watanabe, Ji Ung Lee Recently, the Schottky-Mott (SM) limit has been studied through measurements on many metal-semiconductor junctions with various metals [1]. Here, we probe the SM limit using a single, gate-tunable, hexagonal boron nitride encapsulated graphene-WSe2-graphene heterostructure. One-dimensional edge contacts are made to the graphene and buried split-gates are used to separately tune the electrical properties each graphene-WSe2 junction. By making one graphene-WSe2 junction Ohmic, we perform electrical measurements of the Schottky barrier (SB) formed in the other junction. Electrical measurements of the SB show striking agreement with the ideal-diode equation, with over thirteen decades of drain current modulation via the gate voltage. Arrhenius activation energy measurements reveal one-to-one electrical control of the SB height by the gate voltage. These measurements indicate a stark absence of Fermi-level pinning at the graphene-WSe2 interface, resulting in a tunable SM limited heterojunction. Our findings are of broad significance, enabling fundamental studies of the SM limit and the ability to make superior electrical contact to two-dimensional materials. |
Wednesday, March 6, 2019 11:27AM - 11:39AM |
L54.00002: Naturally formed contacts between assorted metals and 2D TMD materials Ruhi Thorat, Thushan Wickramasinghe, Gregory Jensen, Maryam Bizhani, Eric A Stinaff Novel technologies built on the properties of two dimensional transition metal dichalcogenides (TMD) require the ability to pattern, process, and contact the material in a scalable manner. However, reproducibly making quality contact to 2D materials remains a significant challenge. We have developed a technique which uses bulk transition metal contacts which act as nucleation sites and a source of material for the growth of 2D TMDs. The bulk metal remains after growth, establishing a naturally formed electrical contact with the TMD material. In the original manifestation of this technique, the contact material was limited to the transition metal of the subsequently grown TMD, however, it has been reported that various elemental metal contacts exhibit reduced Schottky barriers. We will present results from a modification of our growth process which allows for different metal contacts to be produced. A comparison between various metal contacts such as Ti-MoS2 and Mo-MoS2 will be presented and transport measurements will be discussed. This modification to our technique opens up the possibility of producing more complex device architectures with tailored contact properties. |
Wednesday, March 6, 2019 11:39AM - 11:51AM |
L54.00003: Direct reversible writing of nanoscale doping patterns in van der Waals heterostructures Wu Shi, Salman Kahn, Lili Jiang, Sheng-yu Wang, Hsin-Zon Tsai, Dillon Wong, Takashi Taniguchi, Kenji Watanabe, Feng Wang, Michael F Crommie, Alex Zettl Spatially controlled modification of charge density is essential to explore exotic physics and enable new device applications. Conventionally, this has been achieved using lithographically defined local gates or by employing molecular self-assemblies on surfaces. However, these methods face limitations in applications necessitating spatial re-writability and complex circuit designs. Recent progress has demonstrated alternative ways to induce rewritable doping patterns in van der Waals (vdW) heterostructures without complex processing masks or resist by optical illumination or applying an STM tip voltage pulse. In this work we introduce a more flexible electron beam doping technique to induce controllable and erasable doping effect in (vdW) heterostructures. With this new doping technique, we can accumulate high carrier density and reversibly write complex doping patterns with nanoscale spatial resolution while preserving the high quality of the vdW heterostructures. The technique can be an ideal approach to study a variety of superlattice physics in vdW heterostructures and to create on-demand circuits for device applications. |
Wednesday, March 6, 2019 11:51AM - 12:03PM |
L54.00004: Effect of Remote Surface Optical Phonon Scattering in Ferroelectric-Gated Single- and Bi-layer Graphene Hanying Chen, Zhiyong Xiao, Anil K Rajapitamahuni, Yifei Hao, Kenji Watanabe, Takashi Taniguchi, Xia Hong We investigate the effect of the remote surface optical (RSO) phonon scattering on the transport properties of single and bi-layer graphene gated by ferroelectric Ba0.6Sr0.4TiO3 (BSTO) thin films. Graphene flakes were exfoliated on epitaxial 100-300 nm BSTO thin films grown on Nb-doped SrTiO3 substrates. Single and bi-layer samples were then identified via optical microscopy and characterized by atomic force microscopy and Raman spectra. Selected flakes were fabricated into field effect transistor (FET) devices via e-beam lithography. At low temperature, these ferroelectric-gated FETs (FeFET) exhibit resistivity hysteresis induced by ferroelectric switching, which evolves to anti-hysteresis at ~40 K. The graphene FETs exhibit high field effect mobility up to µFE~19,000 cm2/Vs and quantum Hall at 10 K, from which we deduced a dielectric constant of ~60 for BSTO. We examined the temperature dependence of the resistivity, which reveals dominant RSO phonon scattering from the interface with BSTO. We also discuss the effect of capping these samples with a top h-BN layer. Our study facilities the development of high-performance FeFETs based on graphene. |
Wednesday, March 6, 2019 12:03PM - 12:15PM |
L54.00005: Quantifying thermal boundary conductance of 2D-3D interfaces Cameron Foss, Zlatan Aksamija Heat dissipation in next-generation electronics based on two-dimensional (2D) materials is a critical issue in their development and implementation. A bottleneck for heat removal from the 2D layer into its supporting substrate is the thermal boundary conductance (TBC) of the 2D-3D interface, which is impacted by their structure and composition. Here we investigate the temperature-dependent TBC of 42 interfaces formed between a group of six 2D materials and seven crystalline and amorphous substrates. Our results show that the TBC can be varied by nearly two orders of magnitude, from 0.6 MW.m−2.K−1 (h-BN on diamond) to 40 MW.m−2.K−1 (h-BN on SiO2), for the same 2D layer by changing the substrate material. We find that amorphous materials boost the TBC due to the low-frequency Boson peak feature in their vibrational density of states (vDOS) relative to their crystalline counterparts, whose vDOS follows a Debye model at low frequency, assuming the two interfaces have the same adhesion. For crystalline substrates, we correlate constituent material properties with the calculated TBCs and find that TBC depends on a combination of the speed of sound, Debye temperature, density of the substrate, and bandwidth of the flexural branch in the 2D material. |
Wednesday, March 6, 2019 12:15PM - 12:27PM |
L54.00006: Towards the Mechanism of Protonic Transport in Graphene Oxide Vladimir Samuilov, Nikolai Poklonski Graphene oxide (GO) has been considered as a good ionic conductor and an electronic insulator simultaneously [1,2]. The mechanism of the protonic conductivity in GO has not been studied carefully yet. |
Wednesday, March 6, 2019 12:27PM - 12:39PM |
L54.00007: AC Josephson effect in a capacitively shunted graphene Josephson junction Fan Yu, Sandesh S Kalantre, Gleb Finkelstein, Francois Amet, James R Williams The AC Josephson effect is being used to detect signatures of novel modes in Josephson junctions. However, complex behavior of these junctions under RF radiation can also from trivial effects, like the presence of a large shunting capacitance. Here we study the AC Josephson effect on a junction made of graphene encapsulated in boron nitride and contacted by electrodes made of a superconducting molybdenum-rhenium alloy. In regions where chemical potential is close to the charge-neutrality point and the RF drive current is comparable with critical current, this device demonstrated a bi-stability between the first Shapiro steps, indicating the Josephson junction is in a chaotic regime. A full description of the chaotic physics observed is presented. These observations cast doubt over arguments that AC Josephson effect in the low RF drive amplitude region would offer the opportunity to observe 4-π current phase relation in topological Josephson junctions. |
Wednesday, March 6, 2019 12:39PM - 12:51PM |
L54.00008: Superconductivity in Graphene NbSe2 heterostructures Satrio Gani, Hadar Steinberg, Enrico Rossi We study van der Waals heterostructures formed by graphene and monolayer NbSe2 . We show that despite the large mismatch between the lattice constant of graphene and NbSe2 in these structures a large superconducting pairing can be induced into the graphene layer. In addition, we show how such pairing depends, both in nature and structure, on the stacking configuration. Our results are relevant also to heterostructures formed by graphene and other monolayer of transition metal dichalcogenides such NbS2, TaS2, and TaSe2, that have also been shown to be superconducting at low temperature, and suggest a way to probe the nature of the multiband superconducting gap in these systems. |
Wednesday, March 6, 2019 12:51PM - 1:03PM |
L54.00009: Superconducting contact to 2D transition-metal dichalcogenide superconductors Michael Sinko, Sergio De La Barrera, Olivia Lanes, Michael Hatridge, Benjamin Matthew Hunt Two-dimensional transition-metal dichalcogenide superconductors have unique and desirable properties for integration with conventional superconducting circuits. These properties include the ability to form atomically clean and flat interfaces with stable tunnel barriers (such as boron nitride), increased kinetic inductance due to the atomically-thin geometry, and resilience to very high in-plane magnetic fields. Integrating 2D superconductors into superconducting circuits requires a fully superconducting contact be made between the 2D material and a conventional superconductor. By means of an in situ process of etching and angled Al evaporation, we present evidence of robust superconducting edge contact to NbSe2 fully encapsulated by insulating hBN. A critical current density Jc = 7x108 A/m2 is achieved in the contacts. In a second set of samples, two contacts are connected with an Al loop to form a SQUID. A Fraunhofer pattern is observed in each of these samples, whose periodicities can be modeled by using an effective area for the SQUID loop equal to the physical loop area plus an area from the thin NbSe2 flake that is uniformly penetrated by the applied magnetic field. |
Wednesday, March 6, 2019 1:03PM - 1:15PM |
L54.00010: Magnetotransport studies in hybrid 2D/0D nanostructures Ethel Perez-Hoyos, Yunqiu (Kelly) Luo, Abhilasha Dehankar, Jinsong Xu, Roland Kawakami, Jessica Winter, Ezekiel Johnston-Halperin We present a device fabrication strategy that takes advantage of stacking techniques developed for van der Waals heterostructures to construct hybrid 2D/0D composite nanostructures, with potential application in the study of spin and charge disorder as well as magnetic-proximity effects. The structures in this study are comprised of superparamagnetic iron oxide nanoparticles (SPIONs) and monolayer graphene. The SPIONs are deposited first using a Langmuir-Blodgett technique, yielding rafts of highly ordered nanoparticles. Characterization via magnetic force microscopy (MFM) reveals magnetic order at multiple length scales and SQUID magnetometry identifies both glassy antiferromagnetic and ferromagnetic response. Single graphene monolayers are mechanically stacked on the SPION layer, and are found to maintain relatively high mobility and gate sensitivity, as indicated by quantum Hall effect (QHE) measurements. |
Wednesday, March 6, 2019 1:15PM - 1:51PM |
L54.00011: Transport measurements on 2D material devices Invited Speaker: Yu Huang Selected by Focus Topic Organizer John Schaibley |
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