Seminars

I. Chair Professor Doctor Rolf Binder
“Nonlinearities and exceptional points in non-Hermitian systems”

Rolf Binder: The aim of this Seminar is to highlight the importance of nonlinear physics in combination with non-Hermitian effects in semiconductors. Many physical systems, including semiconductors, exhibit nonlinear responses to external excitations. A ubiquitous example is the Kerr optical nonlinearity, in which the optical response function depends quadratically on the amplitude of the driving light field. Microscopically, this can be due to various mechanisms, for example Pauli blocking (sometimes called phase-space blocking) or Coulombic interactions between excitons. Interesting phenomena associated with nonlinearities include bifurcations and nonequilibrium phase transitions. Separate from the topic of nonlinearities is the topic of (non-trivial) non-Hermitian effects, which includes the study of so-called exceptional points. While nonlinear optical response and non-Hermitian effects are each active areas of intense research, their combination remains a relatively unexplored frontier. In this seminar, we present state-of-the-art examples of both topics as well as phenomena that result from the combination of the two. The introductory talk Includes a brief discussion of the physical foundation of optical nonlinearities as well as the basics of bifurcation theory, with emphasis on catastrophe theory, and exceptional points.

Rolf Binder, University of Arizona Tucson

Tsuneya  Yoshida, Kyoto University

Tilmann Kuhn, Universität Münster

Denis  Golež, Jozef Stefan Institute

Konstantinos Makris, University of Crete

II. Chair Professor Steven L. Johnson
“Linear and Nonlinear X-ray Probes of Ultrafast Material Dynamics”

Steve Johnson: X-ray probes offer unique opportunities to study the structure and other properties of materials, with advantages stemming from the short wavelength and high energies of x-ray photons.  In this seminar we will review applications of x-ray scattering to the study of materials, with a particular emphasis on what can be learned in the case of materials that are not in equilibrium.  These techniques range from extensions of linear x-ray scattering to the ultrafast time-resolved regime, to new methods of nonlinear spectroscopy that are possible only with the intense x-rays produced at free electron laser sources.

Seminar

Steve L. Johnson, ETH Zurich

Mariano Trigo, SLAC & Stanford University

Daria Gorelova, Brandenburgische Technische Universität Cottbus–Senftenberg

III. Chair Professor Doctor Michael A. Rübhausen
“A Hitchhiker’s guide to Revealing Competing Ordering Phenomena via Time-Resolved Light–Matter Interactions”

Michael Rübhausen: Spontaneous symmetry breaking and the associated emergence of a Mexican-hat potential lie at the heart of many exotic states of matter, including – but not limited to – superconductivity, ferroaxial order, and charge-density waves. Competing ordering phenomena can be investigated in a particularly powerful way using time-resolved light–matter interactions. Most important examples of collective excitations are Higgs, Leggett, and Bardasis-Schrieffer modes in superconductors or exotic ferroaxial amplitudons in charge-density wave systems. Closely related is the hybridization with other degrees of freedom such as phonons and the emergence of gaps in the single particle excitation channel. 

The goal of this focused seminar and tutorial is to bridge the fundamental physics of the Mexican-hat potential and its time-resolved dynamics with cutting-edge time-resolved spectroscopic techniques. It is designed for both experts and students, offering tutorial-style talks and insights into current research developments.

Seminar

Michael Rübhausen, Universität Hamburg

Francesco Barantani, Universität Luxemburg

Jim Freericks, Georgetown University

Tomke Glier, Universität Hamburg

Patrick Klein, Universität Hamburg

Dirk Manske, Max-Planck-Institut für Struktur und Dynamik der Materie

Naoto Tsuji, Tokyo University

IV. Chair Professor Doctor Hans Christian Schneider
“Altermagnets: Optical Response of Altermagnetic Materials”

Christian Schneider:While altermagnets are often envisaged as promising materials for novel functionalities in spin-dependent electron transport, this seminar explores effects which can be induced and/or probed by optical fields in altermagnetic materials on different time scales.

This seminar will cover the basics of light-matter interaction and its relation to the fundamental altermagnetic symmetries in real space and k-space. It will discuss experimental signatures of altermagnets that can be uncovered by optical techniques. Contributions will further address the electronic and magnetization dynamics of altermagnets that can be driven by ultrashort optical pulses, and highlight how the intrinsic altermagnetic carrier dynamics are different from those found in ferromagnets and antiferromagnets.

Seminar

Hans Christian Schneider, Technische Universität Kaiserslautern

Benjamin Stadtmüller, Universität Augsburg

Julen Ibañez Azpiroz, Centro de Fisika des Materiales

Sangeeta Sharma, Freie Universität Berlin