27 September 2021

9:00 - 10:00: Exploring and extending modern particle physics

Bernd Riederer and Fabian Zierler

The main purpose of modern particle physics is to understand the building blocks of our universe on a fundamental level. Up to this day everything we know so far is best described by a quantum field theory (QFT) commonly known as the Standard Model of Particle Physics (SM). Although the SM has been extremely successful, there is still evidence that it is not yet complete. The most convincing arguments for physics beyond the SM (BSM) come from astrophysics, such as a missing explanation for e.g. dark matter. To improve our current knowledge it is therefore necessary to fully understand the implications of the SM as well as systematically search for BSM physics.
In this talk we will give an overview on the various topics that are currently under investigation, by the PhD students in theoretical particle physics, to tackle this problem. These topics cover areas such as finite temperature QCD, the origin and behaviour of dark matter as well as SM- and BSM-Higgs-physics. To cover such a broad spectrum of physics several tools are used ranging from pen-and-paper physics to calculate phenomenological consequences from fundamental theories, up to Monte-Carlo simulations of QFTs on a discretized spacetime.

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10:00 - 10:35: Comparing the enhancement of local and non-local spin-orbit coupling by strong electronic correlations on the honeycomb lattice

Markus Richter

Topological insulators are currently under active research, due to their exotic properties. These materials are insulating in the bulk, but have conducting edge states, which are protected by symmetry. A fundamental role in topological insulators is mostly played by spin-orbit coupling (SOC), as it may cause a non-trivial gap-opening and hence a topological phase. Even though the topological classification is a method that in principle requires band-theory only, correlations caused by coulomb interactions are not unimportant. The question I want to answer here is how SOC is effected by these correlations. In this talk I will first give a brief introduction on topological insulators and how we can define an effective SOC when correlations are present. Following I will present our work on comparing the effect of local interactions on two different models with similar lattice structure (honeycomb lattice) and non-trivial topology driven by SOC. Therefore we take the one-band Kane-Mele-Hubbard model and a model motivated by Bismuthene, which can be viewed as it's two-band equivalent. The main  difference  between  the  two  models concerning SOC is, that in the one-band case the SOC is a purely non-local term, whereas in the two-band case it is purely local. However we find an enhancement of the effective SOC in both cases, the enhancement for non-local SOC is much weaker then for the local one.

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10:45 - 11:20: Absolute Characterization of High Numerical Aperture Microscope Objectives utilizing a Dipole Scatterer

Jörg Eismann

Undoubtably, microscopy is a technique that is of utmost importance to the scientific community. As a result, many people work on the development and fabrication of its key component - the microscope objective. During these processes, a characterization of the microscope objectives is a crucial and essential step. Typically, such measurements are comparative in nature, requiring a calibrated device acting as a benchmark. Consequently, the quality of these elements and their calibration sets an upper limit for the measurement accuracy. In this work, we propose and implement a novel technique for an absolute characterization of high numerical aperture microscope objectives. To circumvent the need for an aberration-less or well-known optical element, our reference wave is created by an object smaller than the wavelength, i.e., a nanoparticle. The emission of such a nanoscale emitter can be calculated analytically and allows us to utilize the scattered light as a nearly-perfect reference wave.

11:20 - 11:55: Sub-picosecond transient absorption of PbS nanocrystals on gold

Dario Grimaldi

We investigate the optical dynamics of PbS nanocrystal layers on a gold thin film by microscopy-based ultrafast pump-probe spectroscopy. The experimental approach enables to precisely probe with femtosecond resolution the transient absorption of nanocrystal films with specific thicknesses in the range from a few to 100 nm, as independently verified by atomic force microscopy. In stark contrast to individual nanocrystal and gold films, the combined system shows a sub-picosecond dynamics that depends on film thickness and probe wavelength. On basis of the observed parameter dependencies we discuss the models for the underlying charge dynamics in our semiconductor/metal system. While of interest for fundamental reasons, the thorough understanding of such effects is of importance for nanocrystal-based electrical and optoelectrical devices.

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13:30 - 14:05: Enhancing and evaluating an analytical model to improve the prediction of solar storm arrivals

Jürgen Hinterreiter

The Sun continously emits particles, the so-called solar wind, and is therefore shaping the heliosphere. Furthermore, our host star ejects clouds of plasma and magnetic field, named coronal mass ejections (CMEs), out in the interplanetary space. CMEs, when directed towards the bodies in the solar system, affect the planetary atmospheres and can lead to strong disturbances. The influence on Earth and the solar system by such phenomena is called Space Weather and is of increasing importance not only for space missions but also for our modern technology on Earth. Over the past years several models were developed to improve the forecast of CMEs. Analytical models such as ELEvoHI (ELlipse Evolution model based on Heliospheric Imager observations) or numerical ones like EUHFORIA (EUropean Heliospheric FORecasting Information Asset). To obtain more accurate Space Weather predictions, we first assess the performance of EUHFORIA, by comparing the modeled speeds with in-situ measurments. We consider only the times of undisturbed (no CMEs) ambient solar wind and apply statistical measures to quantify the model performance. We then make use of ELEvoHI to estimate the arrival times and arrival speeds of CMEs. ELEvoHI obtains the kinematics of CMEs using heliospheric imagers and accounts for the drag force between the CME and the ambient solar wind. When studying the same CME from two different viewpoints, we find that the model may provide quite different results, most probably due to the rigid elliptical CME front assumed. As a consequence, we updated ELEvoHI in such a way that each point of the CME front is able to adjust to the ambient solar wind conditions and find better results regarding the arrival time for the deformed front in comparison to the elliptical front.

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14:05 - 14:40: Understanding Phonon-Related Properties in Metal-Organic Frameworks for Controlling Their Mechanical and Thermal Characteristics

Tomas Kamencek

Metal-organic frameworks (MOFs) are an emerging materials class which, due to their exceptionally large (nano-)porosity, can be used for numerous applications such as gas separation/capture or encapsulation and release of drugs. Functional devices based on these hybrid materials are becoming increasingly important, calling for a precise knowledge of the materials’ mechanical, thermal, electronic, optical, etc. properties. Despite their current popularity and number of possible applications, the physical properties of MOFs – especially those ones which are intimately related to phonons –are either relatively unknown, or at least a fundamental understanding of the role of the different building blocks and their assembly is largely missing. Thus, understanding how the specific building blocks affect the phonons of a MOFs is crucially important to be able to design the related properties. Therefore, we studied the influences of different constituents on the (an)harmonic phonon properties of a variety of MOFs by means of atomistic ab initio simulations.[1] As a starting point, we systematically varied the constituents in isoreticular MOFs (IRMOFs) to separately explore their influence on the phonon dispersion. Here we identified several trends, which can be understood based on classical arguments. Additionally, the acoustic bands (closely connected to the elastic tensor of a crystal) typically show the most notable dependence on the chemical composition of the MOFs. Thus, in a second step, we focused on the elastic properties in MOF-74 as an instructive (non-cubic) representative of this class of materials. [2] Here, we investigated the influence of (i) the metal ions, (ii) the organic inkers, and (iii) water as an adsorbate on the anisotropic mechanical properties (Young’s modulus, linear compressibility, Poisson’s ratio). The derived mechanical properties were comprehensively analyzed to find trends among the systems based on the structural variation connected to deformation mechanisms at a microscopic scale. Building on those results, in a last step, also a typical anharmonic property, the thermal expansion of MOF-74, was investigated. [3] This was achieved by means of a combined experimental and theoretical approach using powder x-ray diffraction and a theoretical treatment within the Grüneisen theory of thermal expansion. Here, we found significant anharmonicities in the interactions of linkers and nodes, suggesting that these are relevant screws to turn to manipulate anharmonic properties. The presented insights form the basis for a future design of materials with tailor-made vibrational, elastic, and anharmonic properties.

[1] Kamencek, T.; Bedoya-Martínez, N.; Zojer, E. Understanding phonon properties in isoreticular metal-organic frameworks from first principles. Phys. Rev. Mater. 2019, 3, 116003, doi:10.1103/PhysRevMaterials.3.116003.
[2] Kamencek, T.; Zojer, E. Understanding the Anisotropic Elastic Properties of Metal-Organic Frameworks: The Instructive Example of MOF-74. J. Phys. Chem. C. 2021, accepted.
[3] Kamencek, T.; Resel, R.; Falcaro, P.; Zojer, E. A combined experimental and theoretical approach to unravel the microscopic origin of the anisotropic thermal expansion in MOF-74. 2021, in preparation.

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Top view of the rhombohedral crystal structure of MOF-74. The black lines denote the edges of the primitive unit cell. Atomic color coding: H…white, C…grey, O…red, Zn…purple.

14:50 - 15:25: Development of nanoporous gold-enzyme hybrid electrodes for application in biosensing and biocatalysis

Elisabeth Hengge

Nanoporous metals, prepared by electrochemical controlled etching, exhibit a free-standing porous structure, large surface-to-volume ratio and high electric conductivity which makes them very interesting materials for (bio-)chemical sensing and (bio-)catalysis. A common approach in the field of biosensing is the immobilization of enzymes to an electrode substrate enabling direct electron transfer from the electrode to the enzymes.

The aim of this interdisciplinary project between the Institutes of Biotechnology and Biochemical Engineering and the Institute of Materials Physics was to establish nanoporous gold (npAu) as a carrier for the enzyme P450 BM3zbasic2 [1] and to explore possible application of this new enzyme electrode. Thereby, the positively charged binding module “zBasic2” was fused to the enzymes which is a novel approach for immobilization on metallic surfaces since it enables electrostatic binding to the electrode surface.

In the first part of the presentation, the surface modification of the nanoporous gold will be discussed which turned out to be essential for the immobilization process.  For this purpose, self-assembled monolayers (SAMs), which are a well-known concept for planar electrodes, have been chosen. However, from literature, very little is known on the assembling process and the final ordering on porous substrate. In this work, in-situ resistometry was established as a method to monitor the adsorption and desorption process and thereby estimate the surface coverage [2]. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to investigate the controllability of the surface charge of the SAMs, revealing that a significant higher fraction of molecules can be controlled compared to planar electrodes [3].

In the second part, selected results on the successful immobilization of P450 BM3Zbasic2 on the SAMs modified npAu will be presented. On average, a surface coverage of 0.6 mg/m2 (equivalent to approx. 2 monolayers) and a remaining enzyme activity of 30% was determined using standard methods from biotechnology. The immobilization process was monitored by UV/VIS spectroscopy as well as electrochemical impedance spectroscopy (EIS) and analyzed by means of electrical equivalent circuit providing in-situ information on the binding process. Successful binding of the enzymes was additionally verified with SEM and FTIR-spectroscopy. EIS was further used to investigate the influence of the surface charge of the SAMs on the immobilization kinetics exploiting the electrochemical controllability of the SAMs.

This work is financially supported by the Lead Project Porous Materials @ Work (LP-03).


[1] D. Valikhani, J. M. Bolivar, A. Dennig, B. Nidetzky, Biotechnol. Bioeng., 2018, 115, 2416-2425.
[2] E. Hengge, E.-M. Steyskal, R. Bachler, A. Dennig, B. Nidetzky, R. Würschum, Beilstein J.
      Nanotechnol., 2019, 10, 2275-2279.

[3] E. Hengge, M. Hirber, P. Brunner, E.-M. Steyskal, B. Nidetzky, R. Würschum, Phys. Chem.
      Chem. Phys., 2021, 23, 14457-14464.

15:25 - 16:00: Physical Insight Into Surface Polymorph Formation for Organic/Inorganic Interfaces

Andreas Jeindl

The ongoing miniaturization in nanotechnology raises the need to understand (and control) the formation of surface polymorphs at a molecular level. Due to the intricate interaction mechanisms, complex physics and high configurational complexity at play, this understanding is still at the very beginning.

In this talk, I will first briefly introduce our in-house-developed structure search algorithm [1] that combines coarse graining, density functional theory and Bayesian learning, to exhaustively predict surface polymorphs.

Then, I will showcase the application of this algorithm to predict and understand the formation of surprisingly diverse surface monolayers for a homologous series of acenequinones on Ag(111). [2] The theoretically predicted structures excellently fit experimental observations within our methodological uncertainties. By performing a detailed analysis of all interaction mechanisms at play, I will further show you how we are able to identify three important driving forces governing the motif formation.

As a last point, the talk will introduce you to our first steps towards predicting electronic interface properties, specifically the role of polymorphism on the work function change, which a monolayer of molecules induces upon adsorption on the surface.[3] By exhaustively predicting the work function changes for millions of polymorph candidates, we can evaluate the work function uncertainties for kinetically trapped as well as thermodynamically stable phases.

[1] Hörmann, Jeindl, et al., Comp. Phys. Comm. 244, 2019
[2] Jeindl, Domke et al., ACS Nano 14, 4, 6723-6734, 2021
[3] Jeindl, Hörmann et al., arxiv.org:2107.00560, 2021


Tommaso Mazzocchi:
Electric field-driven Mott transition: the role of phonons in strongly correlated systems out of equilibrium

Michael Stadlhofer:
Ultrafast Molecular Dynamics in Suprafluid Helium Droplets

Lukas Legenstein:
Devoloping Structure-to-Property Relationships for Thermal Transport in Organic Semiconductors

Alexandra Serebrennikova:
Transport of Volatile Organic Molecules through Paper

Alexander Eber:
VIS/UV Dual Comb Spectroscopy for environmental sensing

Florian Koller:
First results on production of magnetosheath jets during SIRs and CMEs

Johannes Bütow:
SuperPixels - Towards novel integrated photonic sensors with advanced functionality in nano-metrology and imaging