Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V56: Devices from 2D Materials: Function, Fabrication and Characterization - IIIFocus Live
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Sponsoring Units: DMP Chair: Emiliano Pallecchi, Lille University of Science and Technology |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V56.00001: Electrostatically gated quantum dots in van der Waals materials Justin Boddison-Chouinard, Alexander M Bogan, Pawel Hawrylak, Sergei Studenikin, Louis Gaudreau, Andrew Stanislaw Sachrajda, Adina A Luican-Mayer Quantum confinement and manipulation of charge carriers are critical for achieving devices practical for various quantum technologies. Atomically thin transition metal dichalcogenides (TMDCs) have attractive properties such as spin-valley locking, large spin-orbit coupling and high confinement energies which provide a promising platform for novel quantum technologies. In this talk, we present the design and fabrication of electrostatically gated quantum structures based on fully encapsulated monolayer molybdenum disulfide (MoS2) aimed at probing the confined electron states in these structures. Furthermore, we show that laterally gated quantum point contacts successfully pinch-off the current across the device with gate voltages consistent with their lithographic widths. Finally, we discuss the origins of the observed mesoscopic transport features related to the emergence of intrinsically defined quantum dots through the MoS2 channel. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V56.00002: Modulation doping in van der Waals materials: Fabrication of high quality α-RuCl3/graphene heterostructures Jackson Butler, Jesse Balgley, Yiping Wang, Kenneth Burch, Erik Henriksen 2d devices made from van der Waals materials require clean and uniform doping. However, most common techniques used to dope 2d materials either are limited in the carrier densities they can induce, or can degrade sample quality. Recently we discovered that the layered Mott insulator α-RuCl3 can strongly charge dope graphene, inducing a large population of holes of order a few 1013 cm-2 when placed in direct contact. Fortuitously, the graphene is found to maintain a high mobility, achieving the highest reported value at such large induced densities. However, due to the short-ranged nature of this charge transfer, α-RuCl3/graphene heterostructures require careful fabrication procedures to induce uniform doping across typical device scales. In this talk, we discuss particulars of α-RuCl3/graphene device fabrication essential for producing high quality, uniformly doped devices, including using Raman spectroscopy to quantify and pre-screen sample homogeneity, and methods of making low-resistance electrical contact to graphene layers within the stack without degrading sample quality. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V56.00003: Trapping of Interlayer Excitons in MoSe2-WSe2 Heterostructures Daniel N. Shanks, Michael R Koehler, David George Mandrus, Takashi Taniguchi, Kenji Watanabe, Brian J LeRoy, John Schaibley MoSe2-WSe2 heterostructures are known to host long lived spatially indirect interlayer excitons composed of bound electron and hole pairs that are located in different layers. Recently there has been significant interest in spatially controlling interlayer excitons via externally applied electric fields to demonstrate excitonic currents and trapping interlayer excitons via moiré superlattices. In this presentation, I will discuss how to use patterned graphene gates in close proximity to the heterostructure to create a spatially varying electric field within the vicinity of the interlayer exciton. The interaction between permanent dipole moment of the interlayer exciton and the electric field creates a spatial potential energy trap for the excitons, which is controlled by the geometry of the patterned graphene gate as well as the externally applied voltage. I will show that these trapped interlayer excitons can be identified through spatially resolved photoluminescence imaging and gate-dependent spectroscopy. Finally, I will discuss potential applications of the trapped interlayer excitons to quantum information science applications. |
Thursday, March 18, 2021 3:36PM - 4:12PM Live |
V56.00004: Defect-free and water based 2D material inks for printed electronics Invited Speaker: Cinzia Casiraghi Solution processing of 2D materials [1] allows simple and low-cost techniques, such as ink-jet printing, to be used for fabrication of heterostructure-based devices of arbitrary complexity. However, the success of this technology is determined by the nature and quality of the inks used. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V56.00005: Anomalous thermopower oscillations in graphene-NW heterostructures RICHA MITRA Being sensitive to the electron-hole asymmetry, thermopower is an excellent tool for probing the behaviour of local charge puddles near the charge neutrality point in graphene heterostructures. In this work, we present anomalous thermoelectric results measured in Monolayer graphene (MLG)-NW heterostructures. Our devices consist of InAs nanowire (NW) and graphene vertical heterostructure, electrically isolated by thin (~ 10 nm) hexagonal boron nitride (hBN) layers. In contrast to conventional thermoelectric setup, where a heater is placed on one side of a sample, we use the InAs NW as a local heater placed in the middle of the graphene channel. The thermoelectric voltage across bilayer graphene (BLG) in NW-BLG devices shows a change in sign around the Dirac point as predicted by Mott's formula. In contrast, the thermoelectric voltage measured across MLG in NW-MLG devices shows anomalous large-amplitude oscillations around the Dirac point, unrelated to the Mott response estimated from the electrical conductivity data. Using this unique heating geometry, where the temperature gradient is maximum at the centre of the graphene channel, thermopower could capture the local modification in the density of states in graphene, which is manifested as oscillations in thermopower. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V56.00006: Transport Properties of Atomically Thin VI3 Michael Onyszczak, Pengjie Wang, Yanyu Jia, Guo Yu, Tai Kong, Kenji Watanabe, Takashi Taniguchi, Robert Cava, Sanfeng Wu Two-dimensional magnets with strongly correlated electronic states offer exciting opportunities to explore novel quantum phases of matter. The recently synthesized layered van der Waals magnetic insulator VI3 hosts a large charge gap with two phase transitions observed around 80K and 50K in the bulk crystals. In this talk we discuss the properties of two-dimensional VI3 flakes, mechanically exfoliated down to its atomic limit, that are fully encapsulated in hBN with graphite top and bottom gates. We will report our preliminary results obtained from transport studies. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V56.00007: Enhanced Photoluminescence and Strain-driven Localization of Charge Carriers in Multilayer MoS2 on Nanopillars Mounika Vutukuru, Hossein Ardekani, Zhuofa Chen, Kenan Gundogdu, Anna K Swan Funneling of charge carriers and excitons in TMDCs is an exciting venue to control optical quasiparticle locations and density. Application of non-uniform strain provides an energy gradient in the band structure that can achieve funneling. Here we report both exciton and electron funneling in locally strained multilayer MoS2 on nanopillars of SiO2/Si, with the MoS2 film being suspended around the pillar. Spatially resolved Photoluminescence (PL) and Raman mapping show 1.5-2% biaxial strain on the pillar, with strain extending beyond the suspended region. We observe a strong charge increase in the pillar region via Raman A1g red-shift, and a concomitant large increase in the trion contribution in the PL. The increase in radiative trion fraction and Raman A1g shift is attributed to exciton to trion conversion by the strain-funneled electron supply. The indirect material also shows an overall 6-fold increase in the PL intensity due to strain, indicative of exciton funneling, confirmed independently from direct imaging with separate excitation and collection. Our results show that strain control could be used in addition to the electric field, as part of the toolbox for quasiparticle manipulation in 2D systems. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V56.00008: Quantum Hall states in spin-orbit proximitized monolayer graphene Dongying Wang, Mohammed J Karaki, Nicholas Mazzucca, Haidong Tian, Guixin Cao, Kenji Watanabe, Takashi Taniguchi, Chun Ning Lau, Yuan-Ming Lu, Marc Bockrath Spin-orbit coupling (SOC) provides a potential route to controlling spin in devices as well as realizing topological electronic ground states [1]. Graphene/TMDs heterostructures have emerged as a suitable candidate for such devices due to the outstanding electron and spin transport properties as well as the proximity-enabled spin-orbit effects [2, 3]. In this work we use transport measurements to probe quantum Hall ground states in graphene/WSe2 heterobilayers. At low temperature in a perpendicular magnetic field B, we observe all symmetry-broken integer quantum Hall states, yielding spin and valley information. The measured thermal activation gaps at half-filled quartets show significantly different B-dependence for electron or hole doping, deviating from the isolated graphene behavior. We attribute this observation to the proximity-induced SOC, to quantitatively extract the SOC strength, we are developing a self-consistent Hartree-Fock model incorporating Ising and Rashba SOC along with Coulomb interactions. Our work provides insight into the interplay of SOC and interactions in this fascinating system. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V56.00009: Nanophotonic chiral coupling to gate-controlled excitons in monolayer WSe2 Robert Shreiner, Kai Hao, Amy Butcher, Alexander A High Atomically thin semiconductors exhibit pronounced optical responses governed by excitonic resonances, which can be modulated significantly via electrostatic doping. Moreover, their valley character gives rise to circularly polarized optical transitions. The evanescent chirality, then, of tightly confined waveguide modes enables direction-dependent coupling of nanophotonic near-fields to these electrically tunable excitons. Here, we fabricate a gate-controlled van der Waals heterostructure of encapsulated monolayer tungsten diselenide (WSe2) interfaced with a low-loss, high-index titanium dioxide waveguide. We characterize gate-modified directional coupling of exciton emission into the waveguide, which is spectrally resolved to identify peak-dependent chiral coupling efficiencies. This work broadens our understanding of exciton states in two-dimensional materials well-suited for future integration in on-chip photonic technologies. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V56.00010: Characterization of ferroelectric α-In2Se3 field-effect transistors Hanying Chen, Kenji Watanabe, Takashi Taniguchi, Xia Hong We report the study of field-effect transistors (FETs) composed of a ferroelectric van der Waals channel material, α-In2Se3, sandwiched between a SiO2 back-gate and an h-BN top-gate. We mechanically exfoliated 20-70 nm α-In2Se3 flakes and transferred them onto 300 nm SiO2/doped Si substrates, which have pre-patterned Au electrodes. The channel materials were capped by 30-40 nm h-BN, and we transferred multi-layer graphene flakes to the top of h-BN as the top gate electrode. We then characterized the source-drain current-voltage relation (ID-VD) and transfer characteristic (ID-VG) at 300 K. We have switched the channel conduction by over 2x104 using the SiO2 back-gate and 3x103 using the h-BN top gate. The transfer curve shows a clockwise hysteresis, which can be attributed to interfacial adsorbates such as water. We will also discuss the effects of the α-In2Se3 intrinsic polarization, layer thickness of the channel and gate materials, and the environmental factors on the switching characteristics of the FET devices. |
Thursday, March 18, 2021 5:24PM - 6:00PM On Demand |
V56.00011: Nano-synaptic response in graphene oxide by scanning probe microscopy Invited Speaker: Fei Hui Two-dimensional (2D) layered materials have raised most interest and are attractive for the fabrication of high-density electronic devices, due to its atomically thin layer and extraordinary properties (e.g. high mechanical strength, high electrical and thermal conductivity). Vertical resistive memory is recognized as one of the most promising electronic synapses for neuromorphic computing, enabling fast and low-power information procession and storage. However, most memristive electronic neurons and synapses in the literature are very large (area >104 µm2), resulting in low integration density and high-power consumption. In this talk, I will introduce a scalable spray-coating method to fabricate graphene oxide (GO), and the use of an enhanced conductive atomic force microscope (CAFM) setup to analyze nano-synaptic response in ultra-small areas (<50 nm2). I observed that metal/GO/metal nano-synapses exhibit potentiation and paired pulse facilitation at low current levels <1 µA, controllable excitatory post-synaptic currents, and long-term potentiation/depression. This work represents an important advancement to the nanoelectronic characterization of electro-synaptic behaviors in multiple materials, and this technique could generate useful knowledge in the field of high-density and energy-efficient artificial neural networks. |
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