IPS Meeting 2017 - Institute of Physics Singapore

Prof. Michael S. Fuhrer ARC Centre of Excellence in Future Low Energy Electronics Technologies, School of Physics and Astronomy, Monash University	Plenary 1: Topological Electronics
	Wednesday, 22 February, 9:15am
	Energy consumption in the information and communications technology (ICT) sector already accounts for about 5\% of global electrical energy consumption, and is doubling every decade. There is an identified need for a new computing technology with vastly lower energy consumed per operation, but no clear technological solution at present. The discovery in the last decade of topological phases of matter offers a new route to low-energy computation devices. Topological insulators differ from conventional insulators in that the former are guaranteed to have conducting states on their boundaries i.e. edges in two dimensions (2D), or surfaces in three dimensions (3D). These conducting states are generically protected from backscattering and cannot be localized, and, in the case of edge modes of 2D topological insulators, may even conduct current without dissipation. Topological transistors, in which electric or magnetic fields tune a material from conventional insulator to topological insulator, may require less energy for switching than their conventional counterparts, field effect transistors in which an insulator (semiconductor) is tuned to conduction by adding charge. I will discuss how topological insulators arise from basic physical considerations, give some examples of real topological materials being studied today, and give an outlook on what is needed to realise topological electronics.

Nanyang Asst. Prof. Justin Song School of Mathematical and Physical Sciences, Nanyang Technological University	Plenary 2: Anomalous opto-electronics in topological semimetals
	Wednesdat, 22 February, 10:00am
	The “twisting” of electron wavefunctions in crystals, as encoded by Bloch band Berry curvature or band topology, yield anomalous electronic properties that characterize topological materials. In the presence of electron interactions, a rich array of topological phases and behaviors are expected to manifest. I will detail how the combined action of Berry curvature and band topology can dramatically enrich the range of opto-electronic properties found in topological materials. One striking example are a new class of collective excitations – Berry plasmons - that manifest in anomalous Hall metals. Berry plasmons manifest as chiral propagating plasmonic modes, which are confined to system boundaries, and appear even in the absence of magnetic field or topological edge states. A second example are collective modes of Fermi-arc carriers in time reversal broken Weyl semimetals. These chiral fermi arc plasmons possess dispersion relations that are open, featuring hyperbolic constant frequency contours. As a result, a large range of surface plasmon wave vectors can be supported at a given frequency, with corresponding group velocity vectors directed along a few specific collimated directions. Both Berry plasmons and Fermi-arc plasmons can be probed via nanophotonic methods, and are parts of an increasingly rich new tool box to manipulate light in topological matter.

Prof.
Stephen Pennycook
Department of Materials Science & Engineering,
National University of Singapore

Plenary 3: Materials under the microscope: the atomic origin of functionality

Thursday, 23 February, 9:00am

The aberration-corrected scanning transmission electron microscope (STEM) provides real space imaging and spectroscopy with single atom sensitivity. Coupled with first-principles theory, we can now unravel what controls the functionality of surfaces and interfaces, the key to the design of new materials with improved properties. For example, in Nb@C catalysts, we find that single atoms are the active sites, not the numerous nanocrystals that are also present [1]. In BiFeO₃ films grown on La_0.5Sr_0.5MnO_3-x the precise interface termination determines ferroelectric properties [2], and in CdTe solar cells, grain boundaries, long supposed detrimental to properties, are actually found to be beneficial [3]. We can understand the origin of colossal ionic conductivity in strained yttria-stabilized zirconia [4], and the formation of flexible metallic nanowires by electron beam sculpting [5]. In the future we may even be able to determine materials structure and bonding at atomic resolution in three dimensions [6].

[1]	X. Zhang et al.: Catalytically active single-atom niobium in graphitic layers, Nature Communications 4, 1924–1927 (2013).
[2]	Y.-M. Kim et al.: Interplay of Octahedral Tilts and Polar Order in BiFeO3 Film, Advanced Materials, 25, 2497–2504 (2013).
[3]	C. Li et al.: Grain-Boundary-Enhanced Carrier Collection in CdTe Solar Cells, Phys. Rev. Lett. 112, 156103 (2014).
[4]	T. J. Pennycook et al.: Origin of Colossal Ionic Conductivity in Oxide Multilayers: Interface Induced Sublattice Disorder, Phys. Rev. Lett. 104, 115901 (2010).
[5]	J. Lin et al.: Flexible metallic nanowires with self-adaptive contacts to semiconducting transition-metal dichalcogenide monolayers, Nature Nanotechnology, 9, 436-442 (2014).
[6]	R. Ishikawa, S.J. Pennycook, A.R. Lupini, S.D. Findlay, N. Shibata, and Y. Ikuhara: Single atom visibility in STEM optical depth sectioning, Applied Physics Letters 109, 163102 (2016).

Prof. Christos Panagopoulos School of Mathematical and Physical Sciences, Nanyang Technological University	Plenary 4: Spin orbit coupling phenomena at surfaces and interfaces
	Thursday, 23 February, 9:45am
	Recent advances in thin film growth techniques and in calculation capabilities in condensed matter physics have enabled the synthesis of atomically flat surfaces and heterostructures, and the prediction of their electronic properties. A prototype laboratory infrastructure and an integrated network of techniques enable us to study tailor-made materials architectures including magnetoelectrics, ultrathin magnets, superconductors, quantum Archimedean lattices, and atomic scale spin valves. A common thread across several architectures of interest, especially heavy metal compounds and multilayers is that the spin orbit coupling strength at surfaces and interfaces is comparable to the other relevant energy scales, and thus plays a pivotal role. Novel spin-charge phenomena emerge often robust to disorder and thermal fluctuations, with much promise for room temperature applications. I will discuss the notable progress made on Rashba interfaces, symmetry protected states, non-collinear spin textures, and techniques to generate, stabilize and manipulate them in devices. Using particle-like spin structures as a paradigm, I will demonstrate that the states induced by spin orbit coupling and inversion symmetry breaking open a broad perspective with significant impact in the practical technology of spin topology.

Prof. Mark Breese Singapore Synchrotron Light Soruce, NUS Nanoscience & Nanotechnology Initiative, and Department of Physics, National University of Singapore	Plenary 5: The Singapore Synchrotron Light Source
	Friday, 24 February, 9:00am
	Synchrotron radiation is a powerful tool for analytical purposes and for advanced fabrication, which has become indispensable in many disciplines such as the life sciences, materials science, environmental analysis, and micro/nano fabrication. Synchrotron radiation enables us to look into living organisms, man-made materials and advanced engineering components, in vivo, almost non-destructively, in situ, and with spatial and time resolution, revealing detailed structural, chemical, electronic, and magnetic properties. Our superconducting storage ring uses a 700 MeV electron energy and 4.5 Tesla magnetic field to produce synchrotron radiation with a characteristic photon energy of 1.47 keV and characteristic wavelength of 0.845 nm. We have seven Synchrotron beam lines covering the full spectrum of radiated photon energies, from infrared to X-rays of about 10 keV. This presentation will give an overview of SSLS, covering the accelerator, beam lines and range of applications.

Prof. Bryan E. Penprase YaleNUS college	Plenary 6: Chasing Cosmic Explosions: ZTF and Time-domain astrophysics
	Friday, 24 February, 9:45am
	Prof. Penprase will discuss the most luminous sources of radiation in the universe: quasars, supernovae, gamma ray bursts, and merging neutron stars, in the context of his collaboration with astrophysicists at Caltech and worldwide on the "Zwicky Transient Facility" - or ZTF. He will also give an overview of these cosmic explosions, and the technologies on earth and space used to discover and characterize these transient events. With the discovery of gravitational waves from LIGO and an emerging global telescope network, opportunities exist for entirely new types of astronomy and he will explain this new dynamic type of astrophysics that allows astronomers to “chase” these cosmic explosions before they fade away, and what new types of astrophysics they are revealing. The research on such transients has discovered new types of supernovae, new gamma-ray bursts, and gravitational lensing sources. With a global network of telescopes known as GROWTH the time-evolution of the “explosions” is revealing new information about the astrophysics of compact objects, the formation of the elements, and the last moments of stars as they collapse. The new ZTF facility is opening in summer of 2017, and the talk will review some of the capabilities of ZTF and the latest research ongoing with the GROWTH network, and plans for the new research with ZTF.