Physics colloquium in the summer semester 2021

Date: Tuesdays 16.15 (video conference)

Responsible persons: Prof. Nahid Talebi, Prof. Jan Benedikt

Zoom access link

 

 

 

The colloquium will be held as a video conference:
ZOOM Meeting ID: 623 3676 8390
Passcode: 317082

  • 04.05.2021: Prof. Dr. Claudia Draxl (Humboldt-Universität zu Berlin)

    From physics today to publishing and research of tomorrow

    Prof. Claudia DraxlThe growth of data from simulations and experiments is expanding beyond a level that is addressable by established scientific methods. The so-called “4 V challenge” of Big Data –Volume (the amount of data), Variety (the heterogeneity of form and meaning of data), Velocity (the rate at which data may change or new data arrive), and Veracity (uncertainty of quality) – is clearly becoming eminent also in the sciences. Controlling our data, sets the stage for explorations and discoveries. Novel artificial-intelligence tools can find patterns and correlations in data that cannot be obtained from individual calculations / experiments and not even from high-throughput studies. Prerequisites for the ultimate success of data-centric research are a change of our publication culture as well as a FAIR (Finable, Accessible, Interoperable, Re-useable) infrastructure, hosting data from sample synthesis, experiment, as well as theory and computations. I will review the concepts and recent progress of data-driven materials science, addressing the FAIR guiding principles, the importance of Open Data, issues of data quality, and examples of how to turn data into knowledge.

    Inviting person: Prof. Caruso

  • 11.05.2021: Prof. Dr Fabrizio Carbone (École Polytechnique Fédérale de Lausanne)

    Light-Induced phase transitions in strongly correlated systems

    Prof. Fabrizio CarboneUltrashort light pulses offer the possibility to create coherent excitations in solids which evolution can alter the path taken by the material across a phase transition. This can lead to the discovery of exotic out of equilibrium states of matter, and it can provide a unique way to disentangle the different degrees of freedom involved in a phase transition. In this seminar, we will review some recent results obtained by means of ultrafast spectroscopies in strongly correlated systems with a focus on high-temperature superconductors and the prototypical transition metal oxides magnetite and VO2.

    Inviting person: Prof. Talebi

  • 18.05.2021: Prof. Dr. Achim von Keudell (Ruhr-University Bochum)


    Transient atmospheric plasmas – mastering the nonequilibrium

    Prof. Dr. Achim von keudellNon equilibrium atmospheric plasmas form the unique basis for a multitude of applications ranging from thin films, surface modification, plasma chemistry to plasma medicine. In all these cases atmospheric pressure plasmas exhibit an intimate coupling to the bounding surfaces that trigger surface and conversion processes. The complexity of these processes makes a detailed understanding very challenging. Prominent examples are the combination of plasmas and catalysis and of plasmas and electrolysis. Plasmas provide either excited species to change the conversion reaction paths or they alter and may regenerate catalytic surfaces. The analysis requires detailed diagnostics of plasma excitation and surface processes at the plasma-solid or the plasma-liquid-solid interfaces. Three examples are being presented: (i) the conversion of CO2 and of volatile organic compounds is studied in atmospheric pressure plasmas revealing a strong non equilibrium with respect to excitation temperatures and plasma dynamics; (ii) the conversion of water by plasma excitation using nanosecond high voltage pulses that trigger extremely high density plasmas that are governed by field effects at the interfaces and by tunneling in between adjacent water molecules during plasma propagation; (iii) the plasma induced triggering of enzyme driven species conversion in biocatalysis. The work is supported by the SFB 1316 “Transient atmospheric pressure plasmas – from plasmas to liquids to solids”

    Inviting person: Prof. Benedikt

  • 08.06.2021: Prof. Dr. Wolfgang Schleich (University Ulm)

    Quantum carpets: A tool to observe decoherence

    Prof. Wolfgang SchleichQuantum carpets [1] - the spatio-temporal de Broglie density profiles- woven by an atom or an electron in the near-field region of a diffraction grating bring to light [2], in real time, the decoherence of each individual component of the interference term of the Wigner function characteristic of Schrödinger cats. The proposed experiments [2] are feasible with present-day technology.

    Quantum carpets









    References:
    [1] M. Berry, I. Marzoli, and W. Schleich, Quantum Carpets, Carpets of Light, Physics World 14, 39-44 (2001)
    [2] P. Kazemi, S. Chaturvedi, I. Marzoli, R.F. O’Connell, and W.P. Schleich, Quantum carpets - a tool to observe decoherence, New J. Phys. 15, 013052 (2013)

    Inviting person: Prof. Talebi

  • 15.06.2021: Dr. James McIver (Max Planck Institute for the Structure and Dynamics of Matter)
    Ultrafast optoelectronic probes of 2D materials

     Optoelectronic probes offer new opportunities for investigating quantum phenomena in 2D materials on ultrafast timescales and at terahertz frequencies. In this talk, I will report on our observation of a light-induced anomalous Hall effect in monolayer graphene driven by an intense femtosecond pulse of circularly polarized light [1]. We probed electrical transport using an ultrafast device architecture based on photoconductive switches. The dependence of the anomalous Hall effect on a gate potential used to tune the equilibrium Fermi level revealed multiple features that reflect a Floquet-engineered topological band structure [2], similar to the band structure originally proposed by Haldane [3]. This included an approximately 60 meV wide conductance plateau centered at the Dirac point, where a gap of equal magnitude was predicted to open. We found that when the Fermi level was tuned within this plateau, the estimated anomalous Hall conductance saturated around 1.8 ± 0.4 e^2/h.As an extended outlook, I will share our progress on using ultrafast optoelectronic circuits to perform near-field terahertz spectroscopy on graphene heterostructures, which could be used to investigate a wide range of topological and strongly correlated phenomena in 2D materials that often fall on the terahertz energy scale.

    [1] J.W. McIver et al. Nature Physics 16, 38 (2020)

    [2] T. Oka & H. Aoki. Phys. Rev. B 79, 081406 (2009)

    [3] F.D.M. Haldane, Phys. Rev. Lett. 61, 2015 (1988)


    Inviting person: Prof. Bauer

  • 22.06.2021: Prof. Dr. Günther Hasinger (Director of Science, ESA)

    The present and future of ESA's science program

    Exploring the Universe: Synergies and Strategies of the ESA Science Programme
    Science is THE underpinning theme of ESA. As the motor of the spiral of inspiration, innovation, infor-mation exchange and interaction with the Agency’s stakeholders, science is a key unifying theme of the Agency’s activities. Basic science drives innovation and therefore technological advances, lead¬ing to progress and economic development. It drives inspiration and thus the fascination and educa¬tion of new generations of scientists and engineers. It drives information exchange and communica¬tion with the general public that in the end as taxpayers fund the Agency. And it drives the interaction among scientists, with international partners and with stakeholders, ultimately leading to new pro¬jects and the next turn of the spiral. Starting from recent discoveries in astrophysics and space science I give a comprehensive summary of the ESA Science Programme. In particular I will give examples of important synergies between different ESA Science missions. I will also present the new strategic development plan Voyage 2050.

    Inviting person: Prof. Wimmer-Schweingruber

  • 29.06.2021, shifted starting time: 17:15 (!)
    Prof. Dr. Mark J. Kushner  (University of Michigan)

    Prof. Mark Kushner, University of MichiganPlasma 2020 – The US National Academies Decadal Assessment of Plasma Physics: Overview and Future Research Opportunities

    The Board on Physics and Astronomy of the United States (US) National Academies conducts every-10-year assessments of the major fields of physics. The purpose of the decadal assessments is to provide an overview of the progress made in the field over the past decade and to highlight research opportunities in the coming decade. The Plasma 2020 Decadal Assessment of plasma physics, Plasma Science: Enabling Technology, Sustainability, Security, and Exploration, was released in draft form in May 2020 and in final form in April 2021. The report broadly addresses the field of plasma physics, with chapters focused on foundational processes, laser-plasma interactions, high energy density systems, low temperature plasmas, magnetically confined fusion and space plasmas. The Plasma 2020 report, in addition to being a science document of interest to the international community, is also a policy document which responds to the charge of the sponsoring US federal agencies for recommendations on how plasma science should be configured and funded in the US. These agencies are the National Science Foundation, Department of Energy and Department of Defense. As a result, the F&R (findings and recommendations) of the report are US focused, while also hopefully being of interest to the international community by being adaptable to their particular administrative structures.
    In this presentation, an overview of the Plasma 2020 Decadal Assessment will be provided. The Decadal Assessment process will be briefly described, followed by highlights of the accomplishments, science opportunities and F&R across the field. More emphasis and detail will be provided for findings for low temperature plasmas.
    A (free) pdf copy of the Plasma 2020 Decadal Assessment can be downloaded here.

    Inviting persons: Prof. Benedikt, Prof. Kersten

  • 06.07.2021: Prof. Dr. Astrid Veronig, University of Graz (Head of Kanzelhöhe Observatory for Solar and Environmental Research)

    Solar and stellar mass ejections: detection and characterization through coronal dimmings

    Coronal mass ejections (CMEs) are magnetized clouds of plasma that are sporadically ejected by the star’s outer atmosphere and traverse interplanetary space with speeds of thousands of kilometers per second. Solar CMEs are the main source of strong space weather disturbances at Earth, due to the interaction of their magnetic fields and shock waves with the Earth’ magnetosphere. In addition, fast CMEs are often associated with radiation outbursts in the form of flares and high-energetic particle streams inducing further interactions with our planet. Stellar CMEs are supposed to have an even stronger impact on the exoplanets the star is hosting and may even pose a hazard to their habitability. While CMEs ejected by our Sun are regularly imaged by white-light coronagraphs that efficiently block the million-times brighter direct Sunlight, for stars this is not possible. Different approaches have been followed in the past to infer signatures of stellar CMEs, but so far, only few candidates for stellar CME detections are reported. Here we present a new approach, based on the sudden decrease in extreme-ultraviolet and X-ray emission caused by the mass loss during a CME, so-called coronal dimmings. We discuss the first dimming detections associated with flares on late-type stars, indicative for stellar CMEs, and relate them to the dimming-CME observations on the Sun.

    Inviting person: Prof. Heber