Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V40: 2D materials: properties and devices |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Yunqiu Kelly Luo, Ohio State University Room: LACC 501C |
Thursday, March 8, 2018 2:30PM - 2:42PM |
V40.00001: Tunable Excitons in Bilayer Graphene Long Ju, Lei Wang, Ting Cao, Takashi Taniguchi, Kenji Watanabe, Steven Louie, Farhan Rana, Jiwoong Park, James Hone, Feng Wang, Paul McEuen Electrons in monolayer graphene are described by the massless Dirac equation and feature a pseudo spinor. More interestingly, bilayer graphene hosts an electrically tunable bandgap thus allows continuous tuning of the electron mass and the pseudospin. Similar to electron spin, the pseudospin manifests itself as an angular momentum and magnetic moment---both are key in determining the properties of graphene. In this talk, I will discuss our efforts on probing novel tunable exciton physics in gapped bilayer graphene. We observed unusual optical selection rules and extremely large magnetic moments of excitons. These observations are direct signatures of pseudospin effects which can be traced to the Berry curvature microscopically. I will also discuss the connection of these excitons to the valley degree of freedom and the their potential for valleytronic applications. |
Thursday, March 8, 2018 2:42PM - 2:54PM |
V40.00002: Abstract Withdrawn
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Thursday, March 8, 2018 2:54PM - 3:06PM |
V40.00003: Focused Deposition of Individual Ion-trapped Graphene Nanoplatelets in Ultra-high Vacuum Joyce Coppock, Ian McAdams, Jacob Murphy, Bruce Kane A charged nanoparticle that is confined and cooled in an ion trap can, in principle, be expelled from the trap and directed onto a substrate with high accuracy using an electrostatic lens. This technique may be applied to create new types of structures (by depositing a 2D material onto a reactive surface in high vacuum, for example) or to allow characterization of previously trapped particles using conventional microscopy techniques. In this talk, we present a method of depositing an ion-trapped graphene nanoplatelet onto a conducting indium tin oxide (ITO) substrate in ultrahigh vacuum (UHV), using an Einzel lens to focus the platelet’s trajectory. The substrate can be removed from the system for further study of the platelet. We demonstrate detection of deposited platelets by a charge sensor and discuss progress in locating the deposited platelets via image analysis. Finally, we discuss possibilities for depositing 2D materials to create strained or corrugated structures. |
Thursday, March 8, 2018 3:06PM - 3:18PM |
V40.00004: Performance Enhancement of Many-Layer-Graphene based Memristors by Fermi Energy Lowering Xiaochen Zhu, Haoming Jin, Ang Li, Todd Schumann, Arthur Hebard The search for high-performance non-volatile memory structures remains essential for the research and development of resistive random access memory (RRAM) technology. In addition to the extensive exploration of novel materials, the optimization of electrode/interface properties also serves as a primary objective. In this work, we study the resistive switching properties of many-layer-graphene (MLG) /Nb:SrTiO3 (NSTO) interfaces. We find that straightforward bromine intercalation leads to improvements of on/off ratios by more than a factor of 100 and a greater stability, which we attribute to higher Schottky barriers associated with the bromination-induced Fermi energy lowering in MLG. Considering the rapid growth in the discovery and understanding of two-dimensional (2D) material systems, our findings here suggest that, for NSTO and other interface-type RRAM devices, the integration of 2D materials via van der Waals bonding opens new opportunities for the design of novel and emerging RRAM devices with versatile and superior functionalities. |
Thursday, March 8, 2018 3:18PM - 3:30PM |
V40.00005: Graphene acousticelectric latch Ching-Ping Lee, Yu-Peng Hong, Man-Ting Shen, Chiu-Chun Tang, Dah-Chin Ling, Yung-Fu Chen, Cheng-Chung Chi, Jeng-Chung Chen We implement a logic latch by using a graphene-based acousticelectric transducer. We operate two pairs of inter-digital transducers to launch surface acoustic waves (SAWs) on a piezoelectric LiNbO3 substrate and exploit graphene, an intrinsic two-dimensional gas, as channel material to sustain acousticelectric current Iae induced by SAWs. By corporately tuning the amplitude of two SAWs, we can manipulate the propagation direction of Iae so the magnitude and the sign of Iae can be manipulated. We define the Iae zero crossing as Iaeoff, and then demonstrate that Iae can be switched with a ratio Iaeon / Iaeoff ~ 104 at a rate up to few tens kHz. Our device with the newly-developed sensing scheme provides a means to convert incoming acoustic waves modulated by digitized data sequence onto electric signals with frequency band suitable for digital audio modulation. Consequently, it can perform an effective latch operating and, potentially, may open a route for the future development of various logic devices based on two-dimensional materials. |
Thursday, March 8, 2018 3:30PM - 3:42PM |
V40.00006: Transport Properties of CVD Graphene Cooled with a Biased Gate Voltage U. Kushan Wijewardena, Rasanga Samaraweera, Annika Kriisa, Binuka Gunawardana, Tharanga Nanayakkara, C. Rasadi Munasinghe, Ramesh Mani Electron and hole transport in graphene continues to be a topic of theoretical and experimental interest[1-2]. In this experimental work, we examine electron/hole transport in a graphene Hall bar device, where the graphene was prepared using standard chemical vapor deposition on copper foils. This study aims to find the effect of cooling a graphene specimen under a gate bias on the transport characteristics. Thus, we present results from the measurements carried out in a closed cycle refrigerator out over a broad temperature range (295K – 15K), with a focus on the effect of the gate bias voltage on the charge neutrality point. Further we study the behavior of the Hall effect under different gate voltages around the charge neutrality point. |
Thursday, March 8, 2018 3:42PM - 3:54PM |
V40.00007: Attosecond Carrier Dynamics and Electronic Structure Measurements in Quasi-2D Layered Materials Calley Eads, Dmytro Bandak, Mahesh Neupane, Dennis Nordlund, Oliver Monti Two-dimensional layered materials may demonstrate strong quantum confinement effects not only in a single layer but perhaps already in quasi-2D layered crystals. Understanding such effects using electron dynamics would enable tailoring of electronic structure and interfaces of two-dimensional layered materials. Interrogating carrier dynamics on the relevant sub-fs to few-fs time-scales has however been challenging thus far. Here, we use attosecond spectroscopy to investigate quantum confinement effects for the carrier dynamics of SnS2, MoS2 and K-doped MoS2. We demonstrate a layer decoupling mechanism due to strongly anisotropic screening, which leads to two-dimensional character manifest already in layered bulk crystals. |
Thursday, March 8, 2018 3:54PM - 4:06PM |
V40.00008: Material Realistic Description of Coulomb Engineered Two-dimensional Materials Christina Steinke, Malte Rösner, Dmitry Ryndyk, Tim Wehling Heterojunctions are building blocks of various applications in modern optoelectronics. Common heterojunctions rely on interfaces of different materials in order to gain the desired spatial band-gap modulations. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V40.00009: Very high mobilities for holes in strained germanium quantum wells Nico Hendrickx, Amir Sammak, LaReine Yeoh, Diego Sabbagh, Menno Veldhorst, Giordano Scappucci After being supplanted by silicon 50 years ago, germanium is currently making a comeback. Strained germanium quantum wells have superior properties, including very high mobilities for holes and strong spin-orbit coupling, making it a promising candidate material for spin quantum computation. Furthermore, germanium is compatible with industrial silicon technology, such that many concepts can be borrowed to realize advanced devices. |
Thursday, March 8, 2018 4:18PM - 4:30PM |
V40.00010: Structured Two-dimensional Electron Gas Channel for Single-band THz Detector Kiana Montazeri, Pouya Dianat, Zhihuan Wang, Bahram Nabet We have demonstrated that a structured plasmonic channel, with high ratio of the carrier concentration of the stripes can provide the momentum change in the incident photons, in turn, these photons can be coupled to the surface plasmons in the two-dimensional channel of confined electron gas formed at the hetero-interface of a GaAs/AlGaAs HEMT device. The propagation of the plasma wave along the channel generates a voltage difference between the drain and the source of the device that can be electrically measured. Based on the hydrodynamic model of this short channel HEMT device, this voltage is proportional to the quality factor of the resonator and generates resonant peaks at the harmonics of the input excitation, making it a promising candidate for single-band detection. These devices can be used in THz detectors, since the resonant frequency of the plasmons in the channel lies within the range of THz. Terahertz is the frontier range in electronics and optoelectronics for applications in various areas such as radio astronomy, wireless communications, biotechnology, medicine, etc. In HEMT devices, the two dimensional electron gas with the infrequent collisions with impurities and lattice vibrations provides a high quality factor resonant cavity for plasma waves to generate. |
Thursday, March 8, 2018 4:30PM - 4:42PM |
V40.00011: The Seebeck Effect and In-plane Thermal Conductivity of a 2D Metal-organic Framework, Copper Benzenhexathiol: Potential Application to Thermoelectrc Devices Ryuichi Tsuchikawa, Neda Lotfizadeh, Nabajit Lahiri, Shuwan Liu, Mackenzie Lach, Janis Louie, Vikram Deshpande Copper benzenehexathiol (Cu-BHT) is a compound material categorized as metal-organic frameworks (MOFs), and it possesses unusually high electrical conductivity for MOFs [1]. MOFs form in a two-dimensional, thin film structure, and the thickness of our synthesized Cu-BHT film was down to sub-50nm with the lateral dimension of a few tens of microns. We measured the thermal conductivity, electrical conductivity, and Seebeck coefficient of the thin flakes of Cu-BHT. These measured quantities are relevant to the thermoelectric figure of merit, ZT, a measure of the efficiency of the energy conversion from heat to electricity. The ZT value of our Cu-BHT is relatively smaller as compared with Bi2Te3 but is still one of the highest values for MOFs [2]. Fortunately, one of the advangages of using MOFs as thermoelectric devices is that the thermal properties can be chemically modified easily. Owing to this easiness of the chemical doping, the ZT value of the Cu-BHT can be further improved by optimizing the Seebeck coefficient and electrical conductivity. |
Thursday, March 8, 2018 4:42PM - 4:54PM |
V40.00012: Current-Voltage Characteristics of Quasi-1D Monoclinic NbS3-V Devices: Signatures of the Charge Density Wave Transistions Adane Geremew, Guanxiong Liu, Bishwajit Debnath, Ece Aytan, Mathew Bloodgood, Tina Salguero, Roger Lake, Alexander Balandin A strong interest in quasi 2D and quasi 1D Van der Waals materials has led to a renewed attention to layered materials with the charge density wave (CDW) effects. The switching between CDW phases can be utilized for electronic applications. This explains the motivations behind the search for new polymorphs of materials with CDW properties near room temperature. We fabricated devices on recently discovered polymorph of niobium trisulfide, NbS3-V. The material has been prepared by the CVT method. The devices were fabricated using the shadow mask on exfoliated NbS3-V. At T=290 K, we observed two orders-of-magnitude reduction in the electrical resistance. The effect was attributed to the CDW phase transition. This conclusion is supported by ab initio calculations of the phonon dispersion, X-ray diffraction and Raman spectroscopy. M. A. Bloodgood et. al., APL - Materials (accepted 2017). |
Thursday, March 8, 2018 4:54PM - 5:06PM |
V40.00013: In-plane Elastic and thermal properties of free-standing Molybdenum Disulfide Membranes measured using Ultrafast Transient Grating Spectroscopy Taeyong Kim, Ding Ding, Jong-hyuk Yim, Young-dahl Jho, Austin Minnich Molybdenum disulfide (MoS$_{2}$), a member of transition-metal dichalcogenide (TMDC) family, is of intense interest due to its unique electronic and thermoelectric properties. However, reports of its in-plane thermal conductivity vary due to the difficulty of in-plane thermal conductivity measurements on thin films, and an experimental measurement of the in-plane sound velocity has not been reported. Here, we use transient grating spectroscopy to simultaneously measure the in-plane elastic and thermal properties of free-standing MoS$_{2}$ membranes at room temperature. We obtain a longitudinal acoustic phonon velocity of 7000 $\pm$ 40 m s$^{-1}$ and an in-plane thermal conductivity of 74 $\pm$ 21 Wm$^{-1}$K$^{-1}$. Our measurements provide useful insights into the elastic and thermal properties of MoS$_{2}$ and demonstrate the capability of transient grating spectroscopy to investigate the in-plane vibrational properties of van der Waals materials that are challenging to characterize with conventional methods. |
Thursday, March 8, 2018 5:06PM - 5:18PM |
V40.00014: Fractional Pumping and Quasi-energy Winding in Space-time Crystals Xiaotian Zhang, Peng Ye, Taylor Hughes, Ryuichi Shindou Periodically driven systems exhibit exotic topological phenomenons with no analogue at equilibrium have been discovered[1,2,3]. In some cases, the space and time translation symmetry operations can be intertwined giving rise to a so-called space-time crystal[5]. In this case, the conventional Floquet formulation can not be applied. We construct a space-time translation symmetric 1+1D system and demonstrate that this system exhibits a fractional polarization change as well as a fractional quasi-energy winding during a cyclic process. The polarization change indicates a fractional adiabatic pumped charge, while, the quasi-energy corresponds to an electric flux penetrating the space-time unit-cell. When combined, we show that the two fractions are required to be quantized to an integer value, i.e., the underlying Chern number. By utilizing a Rice-Mele model, which exhibits the Thouless pumping effect[6,7], we demonstrate our general formulation numerically. |
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