Speaker: Yoav Banin
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Speaker: Rupert Oulton
Affiliation: Imperial College London
Abstract Details: Semiconductor diode lasers have overcome numerous technological limitations in the 50 years since their first demonstration to become faster, brighter and smaller; however, scaling their size beyond the diffraction limit of light is a more recent achievement, with still uncertain consequences. A number of demonstrations from around the world, now show the capability of metal-based lasers to create and sustain coherent light well below the diffraction limit, by generating and amplifying surface waves on metal surfaces, known as Surface Plasmon Polaritons. This seminar introduces the motivations and construction of 'plasmonic' lasers and discusses their limitations and potential applications. In particular, such laser devices could be the most efficient and compact method of delivering optical energy to the nanoscale. There are two benefits: firstly, the efficiently generated (focused) coherent laser field can be extremely intense; and secondly, vacuum fluctuations within the laser cavity are considerably stronger than in free space. Consequently, plasmonic lasers have the unique ability to drastically enhance both coherent and incoherent light-matter interactions, bringing fundamentally new capabilities to photonic technologies. While there is a great deal of research ahead for plasmonic lasers systems, this work highlights the feasibility of nano-scale light sources and the potential to do laser science at the nanoscale.
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Speaker: Alessandra Lanzara
Affiliation: UC Berkeley and Berkeley Lab
Abstract Details: Recent developments of table top laser sources have changed the way we study and control material properties, previously achieved through chemical substitutions or with static perturbations such as pressure, electric and magnetic fields. In this talk I will present few examples of how the emerging tool of time and angle resolved photoemission spectroscopy is changing the way we study the properties of a variety of 2D materials and how this tool will allow measurements of devices under working conditions; access to hidden states of matter, as well as design of new photo functional materials. The case of unconventional superconductors and graphene will be discussed in details illustrating the power of this unique time-resolved spectroscopy.
About the Speaker: Alessandra Lanzara
Physics Department, University of California, Berkeley, USAÂ Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley USA
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Speaker: Gregory R Stewart
Affiliation: University of Florida
Abstract Details: In the study of the new iron based superconductors, there are not many global correlations. For example, the early statement that Tc is a maximum (in the 1111 materials) when the As-Fe-As bond angle is the 'regular' tetrahedron value of 109.47 degrees has not been born out in, e. g., the 111 LiFeAs. However, one correlation pointed out by Bud'ko, Ni and Canfield (Phys. Rev. B 79, 220516 (2009)) based on samples of the 122 iron based superconductors has since (Kim et al., J. Phys.: Conds. Mat. 23, 222201 (2011)) been confirmed in both the 111 and the 11 iron based superconductors. This correlation concerns the discontinuity, DC, at the superconducting transition temperature and its dependence on Tc. More recent data, and a comparison of this iron based superconductor behavior with BCS superconductors, will be given. This correlation keeps on being borne out and serves as a.) a metric for sample quality; b.) a test whether a newly discovered iron-containing superconductor is of the same class of superconductor as the other known iron based superconductors and c.) a challenge to theorists to explain this behavior.
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Speaker: Marcin Mucha Kruczynski
Affiliation: Bath University
Abstract Details: Because of its atomic thickness and elastic properties, electronic structure of graphene can be significantly modified with external perturbations. In this talk, I will discuss some theoretical models constructed to capture changes in the band and Landau level structure in (mono- and bilayer) graphene due to strain, external electric field and presence of a substrate. In particular, I will talk about strain-induced changes in the topology of the low-energy band structure of bilayer graphene and signatures of pseudo-magnetic field in electronic transport through strained graphene ribbons. I will also discuss formation of minibands in graphene on incommensurate hexagonal substrates (e.g. h-BN) and some peculiarities of the band structure of bilayer graphene in strong perpendicular electric fields.
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Speaker: Feng-Chuan Chuang
Abstract Details: We use first-principles electronic structure calculations to predict a new class of two-dimensional (2D) topological insulators (TIs) in binary compositions of group III elements (B, Al, Ga, In, and Tl) and bismuth (Bi) in a buckled honeycomb structure. We identify band inversions in pristine GaBi, InBi, and TlBi bilayers, with gaps as large as 560 meV, making these materials suitable for room-temperature applications. Furthermore, we demonstrate the possibility of strain engineering in that the topological phase transition in BBi and AlBi could be driven at ∼6.6% strain. The buckled structure allows the formation of two different topological edge states in the zigzag and armchair edges. More importantly, isolated Dirac-cone edge states are predicted for armchair edges with the Dirac point lying in the middle of the 2D bulk gap. A room-temperature bulk band gap and an isolated Dirac cone allow these states to reach the long-sought topological spin-transport regime. Our findings suggest that the buckled honeycomb structure is a versatile platform for hosting nontrivial topological states and spin-polarized Dirac fermions with the flexibility of chemical and mechanical tunability.
[1] Feng-Chuan Chuang, Liang-Zi Yao, Zhi-Quan Huang, Yu-Tzu Liu, Chia-Hsiu Hsu, Tanmoy Das, Hsin Lin, and Arun Bansil, Nano Lett. 14, 2505 (2014).
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Speaker: Giovanni Vignale
Abstract Details: The peculiar band structure of graphene, coupled with electron-electron interactions, is responsible for the breakdown of the Fermi liquid concept in the undoped material. Interesting many-body effects are also predicted to occur in doped graphene layers, where the Fermi liquid picture still applies with an enhanced Fermi velocity. In this talk I review some of these effects, which should be observable in optical and infrared spectroscopies, magnetic susceptibility measurement, and thermal transport measurements.   Due to the lack of Galilean invariance, both the plasmon frequency and the Drude weight in the optical conductivity are significantly enhanced relative to the conventional RPA values. The orbital magnetic susceptibility, which vanishes in the free-electron approximation, is found to be positive, i.e. paramagnetic, with a value that is completely controlled by the electron-electron interaction.  The quasiparticle lifetime is long and leads to a large electronic component of the thermal conductivity, which strongly violates the Wiedemann-Franz law. I review these theoretical predictions vis-a-vis the current state of the experiment.
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Abstract Details: Flatlands Beyond Graphene (FBG) 2014 will bring together world-leading experts in the area of 2D nanomaterials. It will focus on recent advances in controlling and characterising the properties of these materials, with a particular emphasis on electronic, photonic and spintronic applications. This conference builds on one previous meeting in this series held in Bremen in 2013 and 6 conferences of its ancestral series, Nanostructures of Transition Metal Chalcogenides (TMCN) which have run from 2007 to 2012.
The conference will give students an opportunity to meet and interact with leading scientists, combining good scientific discussions with excellent networking opportunities, and for many a first chance to present their results at an international conference. Finally, it represents an opportunity to showcase our new Research Centre, AMBER, to provide an overview of the goals and ambitions and to attract potential new PIs to Ireland. The scientific focus of the conference is the area of two-dimensional nanomaterials with significant implications for future advances in ICT and Energy.
Flatlands Beyond Graphene 2014 will primarily focus on the following topics of current interest:
Synthesis
Exfoliation
Applications single layers and stack
Composites
Spin
New materials
Doping and functionalization (chemical modification)
Thin films
Conference website: http://flatlands2014.com
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Speaker: Alexandra Carvalho
Affiliation: NUS Physics & GRC
Abstract Details: Black phosphorus has recently been brought into the limelight following the unveiling of the curious properties of its monolayer form, phosphorene. While most known 2D materials have hexagonal structures, resembling graphene, phosphorene has a curious waved-like structure that gives its properties an anisotropic 'twist'. In less than one year, the studies of black phosphorus and phosphorene have been multiplying, with exciting results. It has been shown to be a direct-gap or nearly-direct gap semiconductor both on monolayer and multi-layer form that can become an indirect-gap semiconductor, a semimetal or a metal application of uniaxial stress. Experiments in multi-layer material yield carrier mobilities of about 1000 cm2/(Vs). And recently, the isolation of the monolayer form has been announced. The list continues to grow as theoretical studies add high optical absorption, superconductivity, thermoelectricity...
In this talk, I will consider what makes phosphorene so special. As the recent developments are reviewed, we will turn to density functional theory models for further insight into the electronic and optical properties of this material.
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Speaker: Mei-Yin Chou
Affiliation: Georgia Tech, USA & Academia Sinica, TW
Abstract Details: The Dirac-Weyl Hamiltonian for massless fermions describes the low-energy quasiparticles in graphene. Going beyond the monolayer, intriguing physics has been found in few-layer graphene systems. In this talk, I will focus on our recent theoretical and computational studies of a few representative systems. In particular, the quasiparticle states in rotated bilayer graphene systems act as massless fermions with two “flavorsâ€, and interlayer coupling induces neutrino-like oscillations and anisotropic transport. In addition, a rare fractal-like “butterfly†energy spectrum arises under an external magnetic field. These two- dimensional atomic layer systems provide a unique platform to probe the rich physics involving multiple interacting massless fermions.
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