Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session M3: Invited Session: Novel Quantum Phases in Artificial Lattices and Networks |
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Sponsoring Units: DCMP Chair: Steven Louie, University of California, Berkeley Room: Ballroom III |
Wednesday, March 20, 2013 8:00AM - 8:36AM |
M3.00001: Mott-Hubbard Physics in a Patterned GaAs Heterostructure with Honeycomb Topology Invited Speaker: Vittorio Pellegrini This talk considers efforts directed towards the design and exploration of novel collective electron states in artificial lattice structures that are realized in semiconductor heterostructures by nanofabrication methods. These studies reveal striking interplays between electron interactions and geometrical constraints (topology). We focus on the honeycomb topology, or ``artificial graphene'' (AG) [1,2], that supports Dirac fermions. Dirac fermions and the emergence of quantum phases, such as spin liquids and topologically protected states, can be studied by highly demanding inelastic light scattering methods and by electrical transport at low temperatures [3,4]. In particular, we probed the excitation spectrum of electrons in the honeycomb lattice in a magnetic field identifying collective modes that emerged from the Coulomb interaction [4], as predicted by the Mott-Hubbard model [5]. These observations allow us to determine the Hubbard gap and suggest the existence of a Coulomb-driven ground state [4]. Studies of electrons confined to artificial lattices should provide key perspectives on strong electron correlation in condensed matter science. \\[4pt] [1] M. Gibertini et al. Phys. Rev. B RC 79, 241406 (2009)\\[0pt] [2] C.H. Park and S.G. Louie, Nano Lett. 9, 1793 (2009).\\[0pt] [3] G. De Simoni et al. Appl. Phys. Lett. 97, 132113 (2010)\\[0pt] [4] A. Singha et al. Science 332, 1176 (2011)\\[0pt] [5] J. Hubbard. Proc. R. Soc. Lond. A 281, 401 (1964) [Preview Abstract] |
Wednesday, March 20, 2013 8:36AM - 9:12AM |
M3.00002: Dirac Fermions in a Nanopatterned Two-Dimensional Electron Gas Invited Speaker: Cheol-Hwan Park If a lateral periodic potential with triangular (or honeycomb) lattice symmetry is applied to a conventional two-dimensional electron gas (2DEG), the charge carriers behave like massless Dirac ferions [1,2]. A very interesting and useful point of these newly-generated massless Dirac fermions is that, unlike the case of graphene, their properties can be tuned through the external periodic potential. In this presentation, I will review the electronic properties of those newly-generated massless Dirac fermions in an artificial 2DEG superlattice system and will discuss how the elecctronic structure of those massless Dirac fermions changes depending on the external periodic potential [3]. \\[4pt] [1] C.-H. Park and S. G. Louie, Nano Lett. 9, 1793 (2009).\\[0pt] [2] M. Gibertini et al., Phys. Rev. B 79, 241406 (2009).\\[0pt] [3] C.-H. Park et al., in preparation. [Preview Abstract] |
Wednesday, March 20, 2013 9:12AM - 9:48AM |
M3.00003: Designer Dirac Fermions, Topological Phases, and Gauge Fields in Molecular Graphene Invited Speaker: Hari C. Manoharan The observation of massless Dirac fermions in monolayer graphene has propelled a new area of science and technology seeking to harness charge carriers that behave relativistically within solid-state materials. Using low-temperature scanning tunneling microscopy and spectroscopy, we show the emergence of Dirac fermions in a fully tunable condensed-matter system---molecular graphene---assembled via atomic manipulation of a conventional two-dimensional electron system in a surface state. We embed, image, and tune the symmetries underlying the two-dimensional Dirac equation into these electrons by sculpting the surface potential with manipulated molecules. By distorting the effective electron hopping parameters into a Kekul\'e pattern, we find that these natively massless Dirac particles can be endowed with a tunable mass engendered by the associated scalar gauge field, in analogy to the Higgs field. With altered symmetry and texturing of the assembled lattices, the Dirac fermions can be dressed with gauge electric or magnetic fields such that the carriers believe they are in real fields and condense into the corresponding ground state, as confirmed by tunneling spectroscopy. Using these techniques we ultimately fabricate a quantum Hall state without breaking time-reversal symmetry, in which electrons quantize in a gauge magnetic field ramped to 60 Tesla with zero applied laboratory field. We show that these and other chiral states now possible to realize have direct analogues in topological insulators, and can be used to guide or confine charge in nontrivial ways [1]. \break\break [1] Kenjiro K. Gomes, Warren Mar, Wonhee Ko, Francisco Guinea, and Hari C. Manoharan, ``Designer Dirac Fermions and Topological Phases in Molecular Graphene,'' Nature \textbf{483}, 306--310 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 9:48AM - 10:24AM |
M3.00004: Electron-electron interactions in artificial graphene Invited Speaker: Esa Rasanen Recent advances in the creation and modulation of graphenelike systems are introducing a science of ``designer Dirac materials.'' In its original definition, artificial graphene is a man-made nanostructure that consists of identical potential wells (quantum dots) arranged in an adjustable honeycomb lattice in the two-dimensional electron gas. As our ability to control the quality of artificial graphene samples improves, so grows the need for an accurate theory of its electronic properties, including the effects of electron-electron interactions. Here we determine those effects on the band structure and on the emergence of Dirac points, and discuss future investigations and challenges in this field. [Preview Abstract] |
Wednesday, March 20, 2013 10:24AM - 11:00AM |
M3.00005: Quantum Simulation with Circuit QED Invited Speaker: Andrew Houck Superconducting circuits and circuit quantum electrodynamics provide an excellent toolbox for non-equilibrium quantum simulation. In circuit QED, the strong interaction of light with a single qubit can lead to strong qubit-mediated photon-photon interactions. Recent theoretical proposals have predicted phase transitions in arrays of these cavities, demonstrating that complex matter-like phenomena can emerge with such interacting photons. Due to inevitable photon dissipation and the ease of adding photons through driving, these systems are fundamentally open and a useful tool for studying non-equilibrium physics. I will discuss recent experimental and theoretical progress towards realization of these non-equilibrium quantum simulators. I will focus on a localization-delocalization crossover in a pair of coupled cavities, and discuss preliminary measurements of large cavity arrays. I will discuss a variety of available measurements in these systems, including transport, photon number statistics, and a scanned local quantum probe. [Preview Abstract] |
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