Fachbereichs-Kolloquium im SS 2021
(letzte Änderung 16.07.2021, 08:00)
22.04.2021
Jarek kaspar
University of Washington, Seattle, USA
Einladender: Andronic | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
First results from the
Fermilab Muon g-2 experimentThe Muon g-2 experiment searches for signs of new particles and forces by precisely measuring the magnetic moment of the muon and comparing it to similarly exact theoretical predictions. A previous experiment performed two decades ago at Brookhaven National Laboratory revealed an intriguing hint of such new physics. The first result of the Fermilab Muon g-2 experiment agrees with the previous experiment and increases the tension between the experiment and the Standard Model to 4.2 sigma. This result will be presented along with description of the experimental methods and theoretical implications. Future prospects of improving the experimental and theoretical uncertainties will be discussed.
29.04.2021
GIOVANNA MORIGI
Theoretical quantum physics group, Universität des saarlandes
Einladende: Denz | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
Quantum crystals of photons and atoms
The formation of patterns in nature is often determined by the interplay of noise and interactions of different range. Numberless examples are encountered in everyday life and can be described classically. In the nano-world, where the laws of quantum physics are dominant, our understanding is still in its infancy. The dynamics of a quantum many-body system subject to interactions, dissipation and driving forces poses severe theoretical challenges. Understanding the quantum dynamics of these pattern formation processes is an important question of fundamental research and a crucial issue for quantum technological applications, where one aims at robust quantum coherent dynamics in systems of mesoscopic size. A promising and flourishing approach to tackle these questions is offered by the study of ultracold ensembles of atoms coupled to the light fields of high-finesse optical cavities. In these systems quantum structures of photons and atoms emerge from a quantum nonlinear interaction between scattering particles in the presence of noise and dissipation. The inter-atomic interactions are here mediated by multiple scattering of cavity photons and have a long-range character, which makes these systems a unique platform for shedding light into dynamics predicted in other fields of physics, ranging from nuclear physics, nonlinear dynamics, and astrophysics. In this talk I will discuss the basic physical mechanisms leading to crystalline structures of photons and atoms and will review insights gained by theoretical and experimental studies of these systems.
06.05.2021
JULIEN JAVALOYES
universitat de les illes balears, spain
Einladende: Gurevich | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
Emergence and dynamics of spatio-temporal localized structures in passively mode-locked lasers
Nonlinear optical cavities are test benches of pattern formation. In these strongly dissipative systems, self-organization occurs as the result of the interplay between the nonlinearity mediated either by gain, absorption or nonlinear refractive index of the material and the dispersive effects of the cavity. We will review our recent theoretical and experimental results regarding the emergence and the dynamics of temporal and spatio-temporal localized structures in the output of semiconductor mode-locked lasers. We will disclose new instabilities that occur in vertical external-cavity surface-emitting lasers that stem from the influence of third order dispersion. The latter induces the appearance of asymmetrical pulse satellites that destabilize the mode-locking regime, which leads to complex excitable dynamics and pulse explosions. Our work is set within the framework of time delayed dynamical systems. The latter materialize in situations where distant, point-wise, nonlinear nodes exchange information that propagates at a finite speed, which is a particularly suitable approach for the modeling of an optical pulse bouncing between the various elements composing a laser cavity. However, time delayed systems are usually considered devoid of the essential dispersive effects for pattern formation. We will show how dispersion may appear naturally in singular delayed equations, and make the link via a normal form description with the physical properties of Gires-Tournois interferometers.
20.05.2021
Lena f. kourkoutis
school of applied and engineering physis, cornell university, Ithaca (NY), USA
Einladender: Kohl | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
Cryogenic electron microscopy for probing quantum and energy materials
Electron microscopy has enabled imaging of our natural world with exceptional detail. Today, the three-dimensional structure of biomolecules can be studied down to the atomic scale and single defects present in atomically thin materials can not only be identified but also spectroscopically probed. The developments that have enabled these successes in the life sciences and the physical sciences have been recognized by the 2017 Nobel Prize in Chemistry for cryogenic electron microscopy of biomolecules and the 2020 Kavli Prize in Nanoscience for sub-Ångstrom imaging enabled by aberration correction.Despite these breakthroughs in imaging there are entire classes of materials and devices that have not been able to be explored at the relevant microscopic length scales. In this talk, I will discuss our developments of cryogenic scanning transmission electron microscopy (cryo-STEM) which have opened a new window to probing phenomena in quantum and energy materials that have not been accessible before. Focus will be on two areas, lithium metal batteries and their complex electrode/electrolyte interfaces, and charge-ordered phases which permeate the phase diagrams of strongly correlated systems such as layered transition-metal dichalcogenides, colossal magnetoresistive manganites and cuprate high-temperature superconductors. Cryo-STEM provides a real space probe to map local lattice symmetries in these charge ordered phases. Using half-doped manganites as a model system, we demonstrate the importance of lattice coupling for understanding and manipulating the character of electronic self-organization.
© Lena F. Kourkoutis
10.06.2021
MARTIN OETTEL
Institut für angewandte Physik, eberhard karls Universität, tübingen
Einladender: Thiele | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
The Classical Condensed Phases of Matter: Hard Spheres and Other Simple Model Systems
In standard lectures on condensed matter physics for undergraduate students, solids at finite temperatures are introduced through a simple harmonic picture: atoms are trapped in an energetic miminum which mainly arises owing to the potential energy with their neighbors, and they perform small vibrations eventually leading to the picture of a free phonon gas. The liquid state is usually neglected altogether. Here I show that our current understanding of correlations in liquids and solids has come through the study of hard spheres (billiard balls) and that entropy is a major factor in understanding these. A successful analytic theory is classical density functional theory which for hard spheres is built on mainly geometric insights. Based on this, I discuss a novel strategy to improve classical density functional theory for other systems using methods of machine learning.
17.06.2021
JACCO H. SNOEIJER
Faculty of Science and Technology, University of twente, enschede, the netherlands
Einladender: Thiele | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
Soft Interfaces at Contact: Wetting and Instability
The contact of soft interfaces lies at the core of many natural phenomena and technologies, from wetting and coating to the growth of biological tissue. When sufficiently soft, these systems are no longer governed by their elasticity, but interfacial forces (surface tension) take over. Here we present a number of cases where surface tension dominates over bulk elasticity, fundamentally altering the physical phenomena at play. We first discuss a remarkable resemblance between the instability of soft solid cylinders and the breakup of liquid jets into small droplets. We then turn to applications of wetting, where liquid drops are placed either onto soft polymer networks or onto polymer brushes. The resulting droplet spreading dynamics exhibits features that have no counterpart on rigid surfaces, which thereby offers an interesting route for the design of adaptive coatings.
24.06.2021
SARAH HAIGH
National graphene institute, department of materials, university of manchester, uk
Einladender: Kohl | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
Nanoexploring 2D Heterostructures:
Applying atomic resolution scanning transmission electron microscopy for the investigation of novel 2D materials
and the use of 2D heterostructures to advanced electron microscopy imagingIn this talk I will demonstrate how scanning transmission electron microscopy can provide a vital tool for uncovering structure property relationships in 2D materials and their stacked heterostructures. I will illustrate the talk with recent examples of work revealing Kagome lattice domains in twisted transition metal dichalcogenide bilayers, improved superconductive performance on aging in TaS2 and unexpectedly fast ion uptake in 2D clays. In the second part of the talk I will demonstrate how the 2D heterostructure platform can be used to study gas and liquid flow and to allow atomic resolution imaging of the earliest stages of a liquid mixing induced chemical reaction.
08.07.2021
ULRICH UWER
Physikalisches Institut, Universität Heidelberg
Einladender: Andronic | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
With Beautiful Quarks to New Phenomena in Particle Physics:
Recent Results from the LHCb ExperimentMany rare decays of mesons with beauty and charm quarks (B and D-mesons) are strongly suppressed in the Standard Model and can only proceed via quantum-loops. Contributions from physics beyond the Standard Model at high mass scales could significantly alter the predicted quantum corrections and thus the decay properties of the heavy mesons. Rare beauty and charm meson decays are therefore excellent systems to search for new phenomena. They probe physics at mass scales much above the energies accessible at colliders.The LHCb experiment is a dedicated experiment to study B and D-meson decays at the LHC and exploits the unprecedented production rate of these heavy hadrons in the high-energy proton-proton collisions of the LHC. Recent LHCb results for very rare processes with high sensitivity to new physics phenomena will be discussed. An emphasis is put on so called penguin decays for which differences to the Standard Model predictions have been observed for several channels.
15.07.2021
PAUL M. NÄGER
Philosophisches SeMINAR, wwu münster
Einladende/r: Fachbereich/Fachschaft Physik | PDF |
Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21
The Mereological Problem of Entanglement
The discipline of mereology treats the question how parts and wholes relate and has its roots in ancient Greek philosophy. Especially in the 20th century its concepts have been sharpened considerably resulting in a formalism called classical mereology. From this point of view, entangled quantum systems are an anomaly since they are well-known to involve some kind of holism in the sense that the quantum state of the whole cannot be reduced to the quantum state of the parts. Are entangled systems undivided wholes? In this talk I shall argue on the basis of the quantum mechanical formalism that they are not: When two objects are entangled, there are only these objects but no whole, and the holistic entangled property is carried collectively by these objects.https://philarchive.org/rec/NGETMP
Im Anschluss an den Vortrag möchten wir noch auf die im jährlichen Turnus durch die Fachschaft Physik stattfindende
Verleihung des Lehrpreises
aufmerksam machen. Berücksichtigt wird das jeweils vorangegangene Wintersemester und das aktuelle Sommersemester!