Abstracts zum Symposium “IRIS 2018”


Welcome Adresses

Jürgen P. Rabe (Direktor IRIS Adlershof, Humboldt-Universität zu Berlin)
Peter A. Frensch (Vizepräsident für Forschung, Humboldt-Universität zu Berlin)

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Sub 100 meV electron energy loss spectroscopy in the scanning transmission electron microscope - from phonons to core losses in real and momentum space

Quentin Ramasse (SuperSTEM Laboratory and University of Leeds, U.K.)

The properties of materials are increasingly controlled and tuned through defects engineering taking place quite literally at the atomic level, where one of the most powerful means of characterization arguably lies within a combination of low voltage scanning transmission electron microscopy, energy loss spectroscopy and ab initio calculations. Recent instrumentation advances have pushed the spatial resolution of these instruments below 1Å, while providing energy resolution for spectroscopy of <10meV. This contribution will highlight a number of applications of these techniques, including a recently-developed methodology for recoding momentum-resolved energy loss spectra at nm resolution.

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Nanoscale 3-D X-ray tomography and spectromicroscopy

Gerd Schneider (Helmholtz-Zentrum Berlin für Materialien und Energie & Humboldt-Universität zu Berlin)

In the nano-age, humans manufacture complex structures atom by atom to design e.g. their specific functionality.  Therefore, new tools for the analysis of these structures have to be developed. The HZB microscopy group develops novel methods for X-ray imaging to make use out of the unique interactions of X-rays with matter. For this, X-ray optics for the 10-nm scale characterization of the nanostructure, chemical nature, and composition of materials with high energy resolution are engineered and fabricated. The HZB full-field TXM at the BESSY II U41 undulator beamline allows high spectral resolution of E/ΔE=5000 and 10 nm spatial resolution. With this instrument spatially-resolved NEXAFS studies for material sciences can be performed due to the high energy resolution. Additionally, nano-tomography of cryogenic samples had demonstrated its high potential for life sciences.

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Multi-scale characterization in materials science – travelling in space and time

Michael Rauscher, Tobias Volkenandt (Carl Zeiss Microscopy GmbH, Oberkochen)

For the large spectrum of engineering materials from battery electrodes to fiber composites to metal alloys, there exist features from the nanometer scale up to mm and larger which play unique and distinct roles in determining the functionality of that material or device. Central to understanding these multiscale features are a variety of experimental characterization methods, of which microscopy plays a key role. In this talk we will introduce recent advances in microscopy techniques by means of selected case studies.

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Coffee break


2D or not 2D? Metal-free nanomaterials beyond graphene

Michael J. Bojdys (Humboldt-Universität zu Berlin)

There is a lack of crystalline, metal-free 2D-materials “beyond graphene (BEG)” for the construction of electronic devices. Such BEG-materials are highly desirable, because to-date no useful narrow bandgap semiconductors exist that would bridge the gap between wide bandgap transition metal dichalcogenides (TMD) that rely on critical raw materials (CRMs) and metallic graphene. To tackle this fundamental design-problem, we are drawing on our previous, successful synthesis of low-bandgap semiconducting 2D polymers obtained via “on-template” and “on-catalyst” synthesis (e.g. Angew. Chem. Int. Ed. 2014, 53, 7450 and Adv. Mater. 2017, 29, 1703399).

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Quantum dots as a new class of hybrid materials for optoelectronic applications

Armin Wedel (Fraunhofer IAP Potsdam)

Quantum dots (QDs) can provide unique properties such as size-dependent bandgap tunability, narrow emission spectrum, and low-cost solution-based processing. Through these unique advantages, hybrid organic/inorganic QD light-emitting diodes (QD-LEDs) have attracted considerable attention in display and lighting industry. Currently, a major future task in the device development is to substitute Cd-containing QDs with less toxic materials such as InP-based III-V semiconductor. One of the most challenging works in fabricating multilayer QD-LEDs using colloidal QD solution are the combination with charge transport materials.

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Dynamic properties of metal-halide perovskites relevant for optoelectronic devices

Eva Unger (Helmholtz-Zentrum Berlin für Materialien und Energie & Humboldt-Universität zu Berlin)

Metal-halide perovskite semiconductors are an intriguing class of new semiconducting materials for energy conversion technology. Their low enthalpy of formation provides many possibilities to process these materials from solution but chemical reactions induced by light, heat, atmospheric molecules and ion migration cause dynamic and transient phenomena on various different time scales that need to be understood to reliably predict the potential of this emerging material class. This talk will highlight transient phenomena in metal-halide perovskite materials and devices from current-voltage hysteresis to photo-induced phase-segregation and degradation.

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Lunch break


Hyperbolic tilings in soft matter physics

Myfanwy Evans (Technische Universität Berlin)

Two-dimensional surfaces provide a natural way to study three-dimensional structure, think of bucky-balls on a sphere and carbon nano-tubes on a cylinder. Taking the lead from self-assembly processes in biology, two-dimensional hyperbolic minimal surfaces can be used as a scaffold for more complicated spatial geometry. This talk will introduce the idea of using hyperbolic tilings as a precursor to tangled three-dimensional nets and weavings, followed by an interesting case of hyperbolic self assembly in star terpolymer simulations.

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Irreversible Markov chains in statistical physics

Werner Krauth (Ecole Normale Superieure Paris & MPI für Physik komplexer Systeme)

Virtually all current Monte Carlo algorithms are rooted in the detailed-balance condition, that implements reversible stochastic dynamics. But there is much  more to Monte Carlo than detailed balance and the Metropolis/Heatbath paradigm. Indeed, irreversible Markov chains can be conceived very generally for cases ranging from hard-sphere models (in 1D,  they are related to the TASEP) to long-range-interacting particle systems. In the new irreversible sampling framework, thermodynamic equilibrium is often reached on much faster timescales than with reversible algorithms (finite probability flows persist up to infinite times), the system potential is factorized, the Metropolis acceptance is replaced by a consensus rule, and the system energy is never computed.

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Elements of a topological quantum computer

Felix von Oppen (Freie Universität Berlin)

Quantum computers need to maintain quantum coherence of quantum bits over long times, requiring near-perfect decoupling from the environment. Topological quantum computation provides a remarkable and promising route towards this goal. In its hardware incarnation, quantum information is encoded in qubits built on (nonabelian) anyonicexcitations of topological phases and quantum information processing relies on nontrivial behavior of these anyonsunder exchange (braiding). There is currently growing optimism in both academia and industry that the simplest such topological qubit – based on Majoranabound states – can be realized and perhaps even be developed into a topological quantum computer. This talk will describe essential elements of such a topological quantum computer, covering the range from Majorana-based qubits to the implementation of a universal set of quantum gates. The hardware approach can be further enhanced to realize fault-tolerant quantum computation by adding topological quantum error correction, a software-based approach to topological quantum computation which can be seamlessly matched with the topological hardware.

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Poster Session


Nonreciprocal quantum optical devices based on chiral interaction of confined light with spin-polarized atoms

Arno Rauschenbeutel (Humboldt-Universität zu Berlin & Technische Universität Wien)

The confinement of light in nanophotonic structures results in an inherent link between the light’s local polarization and its propagation direction. Remarkably, this leads to chiral, i.e., propagation-direction-dependent effects in the emission and absorption of light by quantum emitters. We employed this effect to demonstrate an integrated optical isolator as well as an integrated optical circulator which operate at the single-photon level and which exhibit low loss. These are the first two examples of a new class of nonreciprocal nanophotonic devices which exploit the chiral interaction of quantum emitters with transversally confined photons.

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Quantum state tomography in low dimensional semiconductor opto-electronic devices

Ulrike Woggon (Technische Universität Berlin)

Quantum state tomography (QST) is a technique to reconstruct the full quantum state from the statistical measurement of the field fluctuations. Combination of QST with a pump-probe setup allows us to directly manipulate the quantum state  on a sub-picosecond timescale. QST is applied to InGaAs quantum dot-semiconductor optical amplifiers (QD-SOA) to retrieve the Wigner function and the photon statistics for a coherent state interacting with QDs with high time-resolution and in the few-emitter limit. We can reconstruct the second order autocorrelation function with higher precision and time resolution compared with classical Hanbury Brown-Twiss experiments.

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Single photon counting in optical quantum technologies

Andreas Bülter, Michael Wahl (PicoQuant GmbH, Berlin)

Photon coincidence detection, coincidence correlation and coincidence counting are fundamental methods in optical quantum technologies. Typical examples are Hanbury-Brown-Twiss setups to study single photon sources, quantum communication and quantum key distribution (QKD), the study of entanglement using Hong-Ou Mandel (HOM) setups or Bell state measurements. For all these applications single photon counting is an ideal tool, since this method records absolute signal arrival times on several detection channels in parallel. The presentation will review the basics of single photon counting and their technical realisation and will give some typical application examples.

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Gerdans Cafe

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