News & Events

Speaker: Jeil Jung
Affiliation: NUS Physics & Graphene Centre
Abstract Details: When atomically thin two-dimensional materials are layered they often form incommensurate non-crystalline structures manifested in moiré patterns found when examined by scanning probes. In this talk I will address theoretically on a methodology based on first principles calculations to build models that incorporate surface interactions between layered materials for general lattice mismatch or angle misalignment. When applied in a heterojunction consisting of graphene and hexagonal boron nitride, we can derive an effective moire pseudospin superlattice Hamiltonian that provides an intuitive platform to understand the role of the substrate on the electronic properties of graphene. I will use this model to obtain information of experimental interest such as the band structure and (local) density of states.
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About the Speaker:

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Speaker: Mirco Milletari
Affiliation: GRC & Department of Physics, NUS
Abstract Details: We reconsider the problem of electron correlations in the low energy theory of Graphene. We derive the low energy interacting theory directly from the lattice model and show that, unlike in previous analysis, off diagonal density-density interaction terms are also present. Using functional bosonization techniques, we show that the model with a long range Coulomb interaction and zero chemical potential can be solved in an essentially exact way. We derive the interacting Green's function, the anomalous dimension and the Fermi velocity renormalization. While some of these results have already been derived by various authors within a renormalization group approach, in our scheme the renormalized Fermi velocity turns out to be finite and independent from the high energy cut-off. Other observables like the momentum distribution function and the interacting density of states are also obtained and show typical Luttinger liquid behaviour.
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Speaker: Vincent Sacksteder
Affiliation: Sch. of Phys. & Math. Sci., NTU
Abstract Details: We obtain the spin-orbit interaction and spin-charge coupled transport equations of a two-dimensional heavy hole gas under the influence of strain and anisotropy. We predict an enhanced spin lifetime associated with a spin helix standing wave similar to the Persistent Spin Helix which exists in the two-dimensional electron gas with equal Rashba and Dresselhaus spin-orbit interactions. We also briefly discuss spin diffusion in graphene with adsorbed impurities. Collaborators: Andrei Bernevig, Quansheng Wu, Aires Ferreira, Ivan Shelykh
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Speaker: Vincent Sacksteder
Affiliation: Sch. of Phys. & Math. Sci., NTU
Abstract Details: We report on intensive numerical studies of topological conduction on the surface of 3-D TIs, including bulk effects. We highlight a bulk effect which provides a second mechanism of protection against disorder, and also bulk-induced deviations from diffusive scattering. Collaborators: Andrei Bernevig, Quansheng Wu, Aires Ferreira, Ivan Shelykh
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Speaker: Philip Phillips
Affiliation: U. Illinois at Urbana-Champaign, USA
Abstract Details: Since its discovery in 1986, high temperature superconductivity has frustrated experimentalists and theorists alike. The frustration comes from the fact that since the interactions are strong, none of the simple cartoon models based on the standard theory of metals apply. Consequently, there is no clear way of interpreting experiments. Further, as there is no agreed-upon way of solving problems in which the interactions are strong, theorists continue to make progress largely based on the strength of their personalities, that is, proof by intimidation. I will describe a new approach to the strongly correlated problem based on a mapping to a gravitational dual. I will emphasize the rudiments of this mapping focusing on the origins of this new approach and give examples of how it has been applied to the classic Mott problem and superconductivity.
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Speaker: Philip Phillips
Affiliation: U. Illinois at Urbana-Champaign, USA
Abstract Details: One of the open problems in strong correlation physics is whether or not Luttinger's theorem works for doped Mott insulators. I will begin this talk by using this theorem to count particles and show that it fails in general for the Mott state. The failure stems from the divergent self energy that underlies Mottness. When such a divergence is present, charged degrees of freedom are present that have no particle interpretation. Such degrees of freedom are well described by the unparticle construction of Howard Georgi's. I will show how a gravity dual can be used to determine the scaling dimension of the unparticle propagator. I will close by elucidating a possible superconducting instability of unparticles and demonstrate that unparticle stuff is likely to display fractional statistics in the dimensionalities of interest for strongly correlated electron matter.
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Speaker: Kazu Suenaga
Affiliation: Nanotube Research Center, AIST, Japan
Abstract Details: In the Nanotube Research Center at AIST, we have been developing the top- level facilities of electron microscopy which enables the atomic resolution analysis of low- dimensional materials. Point defects and edge structures of graphene have been intensively studied with atomic precision in the last decade [1-4]. Because the studies of atomic defects and boundaries are of general interest in the fundamental researches and becoming more and more crucial for technological applications of any nanoscale materials, the atomic scale studies can be also expanded to the other low-dimensional materials. Here I demonstrate some examples for atomic-scale imaging and spectroscopy of various low-dimensional materials with interrupted periodicities. Active 4|8 defects are most recently found to be responsible for plastic deformation of hexagonal boron-nitride (h-BN) layers [5]. Vacancies and edges with radical bonds are also successfully assigned in h-BN [6, 7]. Doping and boundary behaviors of single-layered dichalcogenides (MX2) are intensively studied because they indeed govern the phase transition behaviors between 2H and 1T phases [8, 9]. Possible nano-device assembly made of metallic and semiconducting MoS2 single layers will be also proposed. [1] A. Hashimoto et al., Nature, 430 (2004) pp.870-873 [2] K. Suenaga et al., Nature Nanotech., 2 (2007) pp.358-360 [3] Z. Liu, K. Suenaga, P. Harris and S. Iijima, Phys. Rev. Lett., 102 (2009) 015501 [4] K. Suenaga and M. Koshino, Nature 468, 1088-1090 (2010). [5] O. Cretu, YC. Lin and K. Suenaga, Nanolett., 14 (2014) pp.1064-1068 [6] C. Jin et al., Phys. Rev. Lett., 102, 195505 (2009) [7] K. Suenaga, H. Kobayashi, and M. Koshino, Phys. Rev. Lett., 108 075501 (2012). [8] YC. Lin et al., Adv. Mater. (in press) [9] YC. Lin et al., submitted. [10] The work is partially supported by JST Research Acceleration Programme.
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About the Speaker: Speakers: NUS speakers and Delegates from Italian Graphene Centre The Italian Graphene Centre under the Italian Institute of Technology (IIT – www.iit.it) is collaborating with GRC to organise the 1st NUS-Italian Graphene Centre workshop. Delegates from Italian Institute of Technology will be visiting GRC from March 16 – 18, 2014. The objective of this workshop is to meet the staff from both institutes and explore collaborations, student and postdoc exchange, etc. Click the link below for the schedule of delegates visiting the GRC, Schedule and abstracts
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