Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session T39: Invited Session: Collective Phenomena in Two-Dimensional Atomic Crystals and Their Heterostructures |
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Sponsoring Units: DCMP Chair: Philip Kim, Columbia University Room: Mile High Ballroom 2A-3A |
Thursday, March 6, 2014 11:15AM - 11:51AM |
T39.00001: Graphene, other 2D atomic crystals and their heterostructures Invited Speaker: Kostya S. Novoselov Probably the most important ``property'' of graphene is that it has opened a floodgate of experiments on many other 2D atomic crystals: BN, NbSe$_{2}$, TaS$_{2}$, MoS$_{2}$, \textit{etc}. One can use similar strategies to those applied to graphene and obtain new materials by mechanical or liquid phase exfoliation of layered materials or CVD growth. An alternative strategy to create new 2D crystals is to start with an existing one (like graphene) and use it as an atomic scaffolding to modify it by chemical means (graphane and fluorographene are good examples). The resulting pool of 2D crystals is huge, and they cover a massive range of properties: from the most insulating to the most conductive, from the strongest to the softest. If 2D materials provide a large range of different properties, sandwich structures made up of 2, 3, 4 \textellipsis different layers of such materials can offer even greater scope. Since these 2D-based heterostructures can be tailored with atomic precision and individual layers of very different character can be combined together, - the properties of these structures can be tuned to study novel physical phenomena (Coulomb drag, Hostadter butterfly, metal-insulator transition, etc) or to fit an enormous range of possible applications, with the functionality of heterostructure stacks is ``embedded'' in their design (tunnelling or hot-electron transistors, photovoltaic devices). Of particular interest are the tunnelling structures. Being able to control the thickness with atomic precision and having a variety of different material in disposal allows us to modify both the height and the width of the tunnelling barrier in the wide range. The use of graphene as electrodes and utilising insulating (BN) or semiconducting (MoS$_{2}$, WS$_{2})$ materials as the tunnelling barrier led to the creation of tunnelling transistors and tunnelling photovoltaic devices and the observation of the resonance tunnelling associated with momentum conservation. We will also consider tunnelling in magnetic field and phonon-assisted tunnelling. [Preview Abstract] |
Thursday, March 6, 2014 11:51AM - 12:27PM |
T39.00002: Quantum transport in graphene/hBN heterostructures Invited Speaker: Pablo Jarillo-Herrero Graphene/hBN heterostructures constitute a new two-dimensional system where the electronic properties of the 2D system depend sensitively on the relative angle of rotation between the two constituent lattices. For large angles of rotation, the low energy electronic structure of graphene remains largely unperturbed, leading to ultra-high mobility pristine graphene samples, and where a novel realization of the quantum spin Hall effect will be discussed [1]. For very low angles of rotation, the electronic spectrum of graphene gets modified significantly, with the appearance of set of low energy superlattice Dirac points. Beyond this effect, we have observed an insulating state (at zero magnetic field) which can be described by the carriers acquiring a finite mass, which is correlated with the angle of rotation [2]. The large moire superlattice in such graphene/hBN system results also in the observation of the Hofstadter butterfly in nearly rotationally-aligned graphene/hBN devices [2]. \\[4pt] [1] A. F. Young, J. D. Sanchez-Yamagishi, B. Hunt, S. H. Choi, K. Watanabe, T. Taniguchi, R. C. Ashoori, P. Jarillo-Herrero, Tunable symmetry breaking and helical edge transport in a graphene quantum spin Hall state, arXiv:1307.5104, Nature (in press) \\[0pt] [2] B. Hunt, J. D. Sanchez-Yamagishi, A. F. Young, M. Yankowitz, B. J. LeRoy, K. Watanabe, T. Taniguchi, P. Moon, M. Koshino, P. Jarillo-Herrero, R. C. Ashoori, Massive Dirac fermions and Hofstadter butterfly in a van der Waals heterostructure, Science 340, 1427 (2013) [Preview Abstract] |
Thursday, March 6, 2014 12:27PM - 1:03PM |
T39.00003: Near-field imaging of plasmons, polaritons, and guided waves in ultrathin crystals Invited Speaker: Michael Fogler |
Thursday, March 6, 2014 1:03PM - 1:39PM |
T39.00004: Isakson Prize: Optical properties, many-body interactions, and accessing the valley degree of freedom in transition metal dichalogenides at monolayer thickness Invited Speaker: Tony Heinz . [Preview Abstract] |
Thursday, March 6, 2014 1:39PM - 2:15PM |
T39.00005: Optoelectronics of supported and suspended 2D semiconductors Invited Speaker: Kirill Bolotin Two-dimensional semiconductors, materials such monolayer molybdenum disulfide (MoS$_{2})$ are characterized by strong spin-orbit and electron-electron interactions. However, both electronic and optoelectronic properties of these materials are dominated by disorder-related scattering. In this talk, we investigate approaches to reduce scattering and explore physical phenomena arising in intrinsic 2D semiconductors. First, we discuss fabrication of pristine suspended monolayer MoS$_{2}$ and use photocurrent spectroscopy measurements to study excitons in this material. We observe band-edge and van Hove singularity excitons and estimate their binding energies. Furthermore, we study dissociation of these excitons and uncover the mechanism of their contribution to photoresponse of MoS$_{2}$. Second, we study strain-induced modification of bandstructures of 2D semiconductors. With increasing strain, we find large and controllable band gap reduction of both single- and bi-layer MoS$_{2}$. We also detect experimental signatures consistent with strain-induced transition from direct to indirect band gap in monolayer MoS$_{2}$. Finally, we fabricate heterostructures of dissimilar 2D semiconductors and study their photoresponse. For closely spaced 2D semiconductors we detect charge transfer, while for separation larger than 10nm we observe Forster-like energy transfer between excitations in different layers. [Preview Abstract] |
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