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 A20: Graphene Devices |
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Sponsoring Units: DCMP Chair: KM RUBI, Los Alamos National Laboratory Room: Room 212 |
Monday, March 6, 2023 8:00AM - 8:12AM |
A20.00001: Mechanically reconfigurable electron confinement in vdW heterostructures via sliding gates Andrew Barabas, Ian Sequeira, yuhui yang, Aaron H Barajas Aguilar, Takashi Taniguchi, Kenji Watanabe, Javier D Sanchez-Yamagishi Van der Waals (vdW) heterostructures are very sensitive to their layer structure and orientation, and the low friction between layers allows devices to be reconfigured to modify layer orientation and overlap, which strongly affects their physical properties. We have discovered that microscale gold features deposited on vdW materials can also slide with very low friction. Deposited gold allows for near arbitrary patterning, enabling electrical contact and a strong mechanical grip to move smaller vdW flakes. This greatly expands the scope of possible vdW heterostructure manipulation experiments. |
Monday, March 6, 2023 8:12AM - 8:24AM |
A20.00002: Suppressing remote optical phonon scattering in graphene below room temperature with touch-printed oxide Ga2O3 Matt G Gebert, Semonti Bhattacharyya, Michael Fuhrer We demonstrate a large-area passivation layer for graphene by mechanical transfer of ultrathin amorphous Ga2O3 synthesized on the surface of liquid Ga metal. Temperature-dependent electrical measurements of millimetre-scale passivated and bare CVD graphene on SiO2/Si indicate that the passivated graphene maintains its high field effect mobility, desirable for applications. Electrical transport is often substrate-limited in graphene, resulting from the scattering of graphene electrons by charged impurities and remote optical phonons in the substrate. Surprisingly, the temperature-dependent resistivity is reduced in our passivated graphene over a range of temperatures below 230 K, due to the interplay of screening of the remote optical phonon modes of the SiO2 by the high-dielectric-constant of Ga2O3, and the relatively high characteristic phonon frequencies of Ga2O3. Raman spectroscopy and electrical measurements indicate that Ga2O3 passivation also protects graphene from further processing such as plasma-enhanced atomic layer deposition of Al2O3. |
Monday, March 6, 2023 8:24AM - 8:36AM |
A20.00003: Investigation of Interfacial Charge Transfer in M+/graphene system Sajedeh Pourianejad, Tina Brower-Thomas Interactions and charge transfer between graphene and engineered environment have a critical role in the electronic and optical properties of graphene due to the potential to locally dope or modify the graphene band structure. Metal adatoms on graphene have drawn great attention because of their ability to affect structural/ electronic properties either by creating defects on the graphene lattice or opening a band gap. Incorporating metal atoms such as Hg into single or few-layer graphene is a promising candidate for inducing diverse unique optoelectronic devices. Confocal Raman spectroscopy and X-Ray Photoelectron Spectroscopy (XPS) measurements were used to study doping, strain configuration, and chemical modification of graphene. In addition, Kelvin probe force microscopy (KPFM) was used to investigate the contact potential difference (CPD) and local charge-related phenomena on M+ decorated graphene. Charge mobility was measured by conductive force microscopy (c-AFM). Finally, we speculate two phenomena by stabilizing metal atoms on graphene. First, tunning Fermi level due to charge transfer between M+ and graphene which is induced by lattice defects graphene. And second, opening a band gap by creating a new topological state induced by spin-orbit coupling (SOC). |
Monday, March 6, 2023 8:36AM - 8:48AM |
A20.00004: Defect-assisted resonant tunneling in graphene/carbon-doped hexagonal boron nitride junctions Yuta Seo, Yuki Tsuji, Kei Kinoshita, Momoko Onodera, Satoru Masubuchi, Rai Moriya, Yijin Zhang, Kenji Watanabe, Takashi Taniguchi, Tomoki Machida Tunneling transport is a powerful probe to study variable quantum properties in van der Waals (vdW) heterostructures. Here, we report defect-assisted resonant tunneling in graphene/carbon-doped hexagonal boron nitride (h-BN:C)/graphite vdW junctions, where carbon, a strong candidate for the origin of defect states in h-BN, was intentionally doped into the h-BN barrier by a carbon annealing process. We observed two kinds of resonant tunneling processes in the same device. One is the elastic process, where carriers tunnel directly between the defect electronic state in the h-BN:C barrier and graphene/graphite electrode layers. The other is the inelastic process accompanied by phonon scattering, where carriers tunnel between the defect electronic state and electrode layers with phonon emission and absorption. From the elastic tunneling process, we determined the energy level of the defect electronic state, which is about 100 meV above the charge neutrality point of graphene. In the inelastic tunneling process, phonons in the vdW heterostructure whose energies are 56, 80, 103, 153, 166, 187, and 201 meV mainly contributed to the tunneling. This defect-assisted resonant tunneling was reproduced in different devices and the obtained defect energy level and phonon energies can be explained by the carbon substitutional defects in the h-BN lattice. |
Monday, March 6, 2023 8:48AM - 9:00AM |
A20.00005: Signatures of hyperfine effects in isotopically purified 13C graphene Vincent Strenzke, Jana M Meyer, Isabell Grandt-Ionita, Marta Prada, Hyun-Seok Kim, Martin Heilmann, Joao Marcelo J Lopes, Lars Tiemann, Robert H Blick The hyperfine interaction (HFI) between electron spins and nuclear spins can act as an undesirable dephasive perturbation on the electronic system. At the same time, it can provide a wealth of information when used as an experimental probing technique. In graphene, nuclear effects are usually neglected due to the low natural abundance (1.1 %) of the spin carrying isotope 13C and the p-orbital character of carriers. Still, the magnitude of the HFI in graphene is subject to controversy and yet to be resolved. In this presentation, I will address interaction effects between the nuclear magnetic moments and the electronic system in isotopically purified 13C graphene. We find signatures of nuclear spin induced effects in the analysis of the weak localization phenomenon and in electron spin resonance measurements. These results show possible routes to assess hyperfine effects in van der Waals materials and to investigate the HFI in graphene in further detail. |
Monday, March 6, 2023 9:00AM - 9:12AM |
A20.00006: Magnetotransport in RuCl3- Doped Graphene Devices Dihao Sun, Ziyu Liu, Lloyd W Engel, Jiaqiang Yan, David G Mandrus, Kenji Watanabi, Takashi Taniguchi, Cory R Dean Recently it has been demonstrated that substantial charge-transfer doping may be realized in graphene by laminating to other 2D materials with a large work function mismatch such as α−RuCl3. Here we investigate the device mobility achievable through such charge transfer schemes and compare device performance with conventional electrostatic gating. Magneto-transport in the quantum Hall regime, as well as new device applications based on charge-transfer doping such as for microwave transmission, will be discussed. |
Monday, March 6, 2023 9:12AM - 9:24AM Author not Attending |
A20.00007: Acoustically-induced pseudo-gauge fields and anomalous transport phenomena in graphene Pai Zhao, Chithra H Sharma, Lev Mourokh, Vadim Kovalev, Lars Tiemann, Robert H Blick We will show that acoustically stimulated carrier transport in graphene at 4 Kelvin signals the presence of artificial gauge fields through the build-up of a transversal voltage at zero magnetic field. We fabricated a graphene Hall bar on a hybrid piezoelectric LiNbO3 on insulator substrate. A nearby interdigitated transducer (IDT) can launch a surface acoustic wave (SAW) that acoustically accelerates the carriers in the graphene layer. The propagating SAW induces an acoustic current. At zero magnetic field, we observe acoustically-induced synthetic Hall voltages, depending on the carrier type, concentration and the SAW power. The synthetic Hall voltage can modulate a conventional Hall voltage arising in a large external magnetic field. Our observation is consistent with studies of strain-induced pseudo-gauge fields. [1] We developed a model that successfully maps the mechanical deformation within the graphene, precipitated by the SAW in the substrate, to the presence of a gauge field and the observed synthetic Hall voltage. [2] |
Monday, March 6, 2023 9:24AM - 9:36AM |
A20.00008: Towards an on-chip terahertz acoustic wave source based on graphene devices. Aaron H Barajas Aguilar, Jasen Zion, Ian Sequeira, Andrew Barabas, Takashi Taniguchi, Kenji Watanabe, Javier Sanchez-Yamagishi In graphene devices, the electronic drift velocity can easily exceed the speed of sound in the material at moderate current biases. Under this condition, stimulated phonon emission dominates over absorption and can produce an exponential growth of the phonon population in the direction of the carrier flow. Here, we demonstrate that phonon amplification can significantly affect the electrical properties of long clean graphene devices, increasing its resistivity up to 7 times over a distance of 8 microns. These effects are observable at a wide range of carrier densities (0.5×1012 to 4×1012 cm-2) and at temperatures from 1.5 to 280 K. Due to the ease of reaching the emission condition, phonon amplification should be considered when measuring electrical transport in long graphene devices. These findings could lead to a new method of room temperature on-chip generation and detection of acoustic waves in the THz frequency range. |
Monday, March 6, 2023 9:36AM - 9:48AM |
A20.00009: Resonantly Enhanced Electromigration Forces for Adsorbates on Graphene Young Woo Choi, Marvin L Cohen We investigate the electromigration forces for weakly bonded adsorbates on graphene by using density-functional based calculations. We find that the nature of electromigration forces on an adsorbate critically depends on the energy level alignment between the adsorbate state and the Fermi level of the graphene. For a resonant adsorbate, whose frontier orbitals lie close to the Fermi level, the electromigration force is dominated by the electron wind force that is strongly enhanced along the electron flow direction, irrespective of the sign of the adsorbate charge. For a nonresonant adsorbate, the electromigration force is essentially the direct force that depends on the adsorbate charge. We also show that the magnitude of electromigration forces can be continuously tunable through electrostatic gating for resonant adsorbates. Our results provide new insight for understanding and controlling how nanoscale objects behave in or on host materials. |
Monday, March 6, 2023 9:48AM - 10:00AM |
A20.00010: Scanning tunneling potentiometry of magnetotransport in graphene Zachary J Krebs, Wyatt A Behn, Keenan J Smith, Pathak Shubham Parashar, Michael M Fogler, Victor W Brar In this work, I will show scanning tunneling potentiometry (STP) measurements of quasiparticle flow around electrostatically defined, micron-scale quantum wells in ultraclean graphene over a range of carrier densities and applied magnetic fields approaching the quantum Hall regime. These STP measurements reveal complex interference patterns that appear in the ballistic regime and reflect the underlying shape of the graphene Fermi surface. As magnetic fields are applied, we observe changes in the local potential profile that reflect the quasiclassical motion of the carriers around the quantum well. As the field is increased, our measurements reveal signatures of the carriers becoming semi-localized around the potential. We interpret our results in the context of localized states and finite conductance paths that form in the presence of disorder in quantum Hall systems. |
Monday, March 6, 2023 10:00AM - 10:12AM |
A20.00011: Probing the magnetization of monolayer graphene via microwave spectroscopy Xinyi Du, Yiwei Le, Yashika Kapoor, Erik Henriksen The magnetization of graphene and graphene-related materials has been of long-standing interest. Disorder-free monolayer graphene is theoretically predicted to have a divergent susceptibility at zero temperature and magnetic field. However, this interesting regime has been little explored. Here, we propose a new approach to measure the magnetization based on high-quality-factor microwave resonators, whose resonant frequency is sensitive to small changes in the quantum capacitance of a graphene device coupled to the resonator. In this talk, we will present details of the measurement approach, estimates of the sensitivity, and initial experimental results. |
Monday, March 6, 2023 10:12AM - 10:24AM |
A20.00012: Hong-Ou-Mandel experiment in a graphene interferometer Himadri Chakraborti, Alexandre Assouline, Leo Pugliese, Lou Bernabeu, Kenji Watanabe, Takashi Taniguchi, Christian D Glattli, Norio Kumada, Patrice Roche, Francois D Parmentier, Preden Roulleau The Hong Ou Mandel experiment, a two-particle interference effect, probes the indistinguishability and the quantum statistics of particles. It relies on the exchange amplitude phase which is 0 for bosons, π for fermions and any intermediate statistical phase for anyons. However, probing the quantum statistics demands synchronized, coherent and indistinguishable excitations at the single electron-level. Graphene that shows a high degree of coherence at the single electron level is a very promising material for two-particle interference. In this study, we show that when two single electron excitations are sent on a graphene beam splitter the exchange effect leads to a two-particle interference effect that is detected in the zero-frequency current correlation. We then extend our work to the electronic Mach Zehnder where the two-particle interference is now both governed by the exchange amplitude term and the Aharonov Bohm phase. We demonstrate the possibility to encode the information into the orbital part of the two-particle wave-function and tune its phase while it is propagating enabling to compare the single particle coherence to the two-particle one. We finally perform the quantum tomography protocol. This works open the way to particles braiding or entanglement of electron flying quantum bits in graphene. |
Monday, March 6, 2023 10:24AM - 10:36AM |
A20.00013: Doping-induced resistive switching in graphene: A theoretical case study on the alpha-alumina|graphene interface Renan Da Paixao Maciel, Chin Shen Ong, Daria Belotcerkovtceva, Yaroslav O Kvashnin, Danny Thonig, Olle Eriksson First-principles calculations reported here illuminate the effects of the interfacial properties of α-Al2O3 and graphene, with emphasis on the structural and electronic properties. Various contact interfaces and different α-Al2O3 surface terminations are considered with on and slightly-off stoichiometric aluminium oxide. We show that depending on whether aluminium or oxygen is in contact with graphene, an sp3 structural deformation and spontaneous spin-polarization may occur next to the interface contact. Interestingly, some cases cause a p-type doping in the graphene band structure, depending on the initial α-Al2O3 geometry placed on graphene. The importance of leaving the surface dangling bonds of alumina saturated or not is also highlighted, and we show that it might be a control mechanism for opening a gap in graphene by the influence of the sp3 bond between oxygen and carbon atoms at the interface. We discuss the potential of utilizing this sensitivity for practical application |
Monday, March 6, 2023 10:36AM - 10:48AM |
A20.00014: Strange-Metal Behavior of Highly Disordered 2D Electron System in Epitaxial Graphene Grown on 6H-SiC Kibog Park, Jaehyeong Jo, Eunseok Hyun, Jiwan Kim, Hyunjae Park, Junhyung Kim, Gahyun Choi, So-Dam Sohn, Jan Kunc, Daejin Eom The electron transport properties of highly disordered 2D electron system in an epitaxial graphene (EG) film grown on a Si-face semi-insulating 6H-SiC substrate have been investigated as functions of temperature and magnetic field. Although the EG film was grown in confinement-controlled manners, the film morphology was noticed to be uneven, mixture of uphill and downhill step structures accompanied with point defects (vacancies), in atomic force microscopy and scanning tunneling microscopy images. This irregular morphology can make the electrons in the EG film disordered and also face randomly-distributed scattering centers in their transport through the film. In magnetotransport measurements, the negative magnetoresistance was observed for a wide range of out-of-plane magnetic field up to 9 T with weak localization signature near zero magnetic field. In temperature dependence of resistivity, the Kondo-like feature was observed with the temperature of minimum resistivity at ~120 K with no magnetic field applied. The minimum resistivity temperature was found to decrease as the magnetic field increases. Most interestingly, a broad regime of T-linear resistivity above the minimum resistivity temperature to room temperature was found to exist, which is the distinct characteristic of strange metal. The disordered aspect of electrons and the potential local magnetic moments residing in point defects are likely to arouse the intriguing electron transport properties observed experimentally. |
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