Bulletin of the American Physical Society
2017 Annual Meeting of the APS Mid-Atlantic Section
Volume 62, Number 19
Friday–Sunday, November 3–5, 2017; Newark, New Jersey
Session P2: CMP-QM: Topological Materials - III |
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Chair: Valery Kiryukhin, Rutgers University Room: 240, Campus Center, NJIT |
Sunday, November 5, 2017 2:45PM - 3:21PM |
P2.00001: Artificially Structured Semiconductors to Model Novel Quantum Phenomena Invited Speaker: Aron Pinczuk Research in this project seeks to design, create and study a class of tunable artificial potentials superimposed on two-dimensional systems in semiconductor quantum structures of high perfection. This project started about four years ago with studies of `artificial graphene' (AG) in semiconductor quantum wells in which a set of quantum dots are positioned in the pattern of a honeycomb lattice. Among major achievements are the realizations of very small period artificial lattices with honeycomb topology in wells. These milestones define a new state-of-the-art in fields of research and nano-fabrication of GaAs. In optical experiments we uncovered evidence that free electrons in these small period AG lattices support massless Dirac fermions (MDF) at the K-points in the Brillouin zones of the artificial lattices [3]. The appearance of MDF's are key features that arise from the symmetry of the honeycomb lattice. The successful modulation doped GaAs quantum wells. In our recent work the periods of the `artificial graphene' (AG) lattices extend down to a$=$40 nm [1,2]. The small periods achieved are about three times smaller than previously reported in GaAs quantum modulation of electron states by superimposed nanoscale potentials offers opportunities for creation of quantum simulators in advanced semiconductor quantum structures. [1] D. Scarabelli, S. Wang et al., J.Vac. Sci. Technol. B 33, 06FG03 (2015). [2] S. Wang, D. Scarabelli, Y. Y. Kuznetsova et al., Appl. Phys. Lett. 109, 113101 (2016). [3] S. Wang, D. Scarabelli, Lingjie Du, Yuliya Y. Kuznetsova, Loren N. Pfeiffer, Ken West, Geoff C. Gardner, Michael J. Manfra, Vittorio Pellegrini, Shalom J. Wind, and Aron Pinczuk, Nature Nanotechnology, accepted for publication. [Preview Abstract] |
Sunday, November 5, 2017 3:21PM - 3:33PM |
P2.00002: Artificial Graphene in Nano-patterned Triangular Antidot Lattices on GaAs Heterostructures Lingjie Du, Sheng Wang, Shalom Wind, Loren Pfeiffer, Ken West, Saeed Fallahi, Michael Manfra, Vittorio Pellegrini, Aron Pinczuk Artificial graphene (AG) in semiconductors have recently been realized in honeycomb quantum dot lattices superimposed on a GaAs quantum well [1], serving as quantum simulators for probing novel electron behavior. Here we report the realization of AG in nano-patterned triangular antidot lattices on the GaAs quantum well [2]. Using cutting-edge fabrication technology we created small-period triangular antidot lattices reaching periods as small as 70 nm (equivalent to 40nm in a honeycomb lattice). The electron states were explored by resonant inelastic light scattering (RILS) at low temperature. Massless Dirac Fermions (MDF) are clearly revealed in RILS spectra due to low-lying transitions between AG bands and in spectra due to combined intersubband transitions. Control of the created MDF through tuning the antidot potential will be discussed. [1] S. Wang, et al., Nature Nanotechnology accepted for publication. [2] L. Du, et al., in preparation. [Preview Abstract] |
Sunday, November 5, 2017 3:33PM - 3:45PM |
P2.00003: Nearly triple point topological phase in half-metallic GdN Jinwoong Kim, Heung-Sik Kim, David Vanderbilt Recent developments in topological semimetals open a way to realize relativistic high-energy particles inside a condensed matter system. For instance, two-fold and four-fold degenerate band crossing points in the momentum space behave as Weyl and Dirac Fermions, respectively. One of the lately studied topological particles is the triple point which is a three-fold degenerate band crossing point. By employing \emph{ab-initio} tight-binding calculations, we investigate topological phases of half-metallic GdN. The crossing points between valence and conduction bands are found to be the type-I triple points in the absence of the spin-orbit coupling. By introducing the spin-orbit coupling, the degeneracy of the triple points is lifted where the amount of splitting depends on the direction of the net magnetic moment. Upon the magnetic moment direction, it ranges from Weyl semimetal to "nearly triple point" phase. The latter phase is revealed to induce apparently equivalent surface states to that of a true triple point. Therefore, half-metallic GdN is a good platform to investigate the triple point phase with rich topological surface states manipulable via the magnetic moment. [Preview Abstract] |
Sunday, November 5, 2017 3:45PM - 3:57PM |
P2.00004: Symmorphic linked nodal rings in semiconducting layers Yuanping Chen, Yuee Xie, Heung-Sik Kim, David Vanderbilt The unique properties of topological semimetals have strongly driven efforts to seek for new topological phases and related materials. Here, we identify a critical condition for the existence of linked nodal rings (LNRs) in symmorphic crystals, and propose that three types of LNRs, can be obtained by stacking semiconducting layers. Several honeycomb structures are suggested to be topological LNR semimetals, including layered and “hidden” layered structures. Transitions between the three types of LNRs can be driven by external strains. Interesting surface states other than drumhead states are found in these topological materials. A tight-binding (TB) model and a k*p model are used to explain the relations between the topological phases and how they evolve into one another. [Preview Abstract] |
Sunday, November 5, 2017 3:57PM - 4:33PM |
P2.00005: Metal-metal bonding and phase transitions in 5d transition-metal chalcogenides Invited Speaker: Valery Kiryukhin Metal-metal bond formation tendency is highly prominent in 5d compounds. It often defines their crystallographic structures, and provides the dominant mechanism for many unusual phase transitions. Herein, we discuss the role of metal-metal dimerization and bonding in the structural and electronic phase transitions in several iridium chalcogenides, concentrating on x-ray scattering studies. We present examples of the transitions with unconventional reconstructions of the Fermi surface in metals, as well as metal-insulator transitions. Temperature induced infinite-staircase-like reentrant transitions between spin-polarized and unpolarized electronic bands, formation and destruction of type-II Dirac points in the band structure, as well as unconventional superconducting states are discussed. A brief summary of the experimental and theoretical aspects of the nature of the metal-metal bond in the presence of large spin-orbit coupling characteristic to the 5d elements is also given. [Preview Abstract] |
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