Magnetic confinement fusion research is developing the scientific and technical basis for realizing a fusion power plant based on the confinement of a burning high temperature fusion plasma. Confinement and stability properties of magnetically confined plasmas are increasingly well understood and the actual confinement values achieved, when extrapolated to a fusion power plant, are close to the required values. Only recently, the European fusion experiment JET achieved a world record of the fusion energy produced. The international project ITER is aiming at a burning fusion plasma with 500 MW of fusion power. While the design of ITER is based on the tokamak concept, stellarators promise a more economic fusion power plant. However, to overcome fundamental disadvantages their design needs an elaborate optimization procedure. The Wendelstein 7-X device in Greifswald is a first-of-a-kind stellarator based on such an optimized design. It went into operation in 2015 and on its way to a 30 minutes high power plasma already demonstrated many of its special characteristics.

The presentation will discuss status and prospects of magnetic confinement fusion R&D, put the Wendelstein 7-X project into a broader perspective and also briefly address the recent milestones achieved by inertial confinement fusion experiments.

Phase transitions are heterogenous phenomena that we experience every day. If we watch a pot boil as we heat it, we see gas bubbles form in specific places and they grow in size as the water gets hotter and over a certain range the water can coexist in both liquid and gas phases. Over the last few decades, we have shown that there is an alternative route to driving phase transitions, not with heat, but with light. By using ultra-short pulses of light, we can drive phase transitions on femtosecond timescales and in some cases access phases that are not accessible to heat alone. The question we seek to address is, do these type of non-equilibrium phase transitions follow the same pathway as our boiling water? Are they heterogenous? or does some other mechanism come into play?

This question has been difficult to answer, because while we have probes that can produce static images with exceptional spatial resolution, or capture dynamics with exquisit temporal resolution, we have not had probes that can do both at the same time! In this talk, I will show how using coherent X-rays from an X-ray Free Electron Laser can achieve both simultaneously, and I will present our first works on imaging ultrafast, light-driven phase transitions at the nanoscale.  

In oxide materials science, the „nothing” is mighty: The key to shaping the physical functionalities of oxide quantum materials and heterostructures lies in the tunability of their oxygen sublattice and, in particular, their defect structure. Initiating or suppressing oxygen migration or redox reactions is an effective means to create targeted oxide phases and unique material properties in confined systems. But what mechanisms govern oxygen-driven redox mechanisms in ultrathin oxide films and at oxide interfaces, and how can they ultimately be controlled at the nanometer scale? We will elucidate how the control of metastable phases and reversible phase transitions leads to an unprecedented versatility to tune electronic conductivity, ferro(i)magnetic and ferroelectric properties at will - uncovered by the compelling capabilities of photon-based electron spectroscopy techniques to explore quantum materials.

Living matter is highly dynamic and organizes in complex patterns and spatial structures. Cells and tissues are driven far from thermodynamic equilibrium by a supply of chemical energy via metabolic processes. I will discuss how active processes drive cells away from thermodynamic equilibrium and I will present general concepts from irreversible thermodynamics that capture the physics of active processes. Fluid flows generated by material contraction driven by active mechanical stresses provide a general mechanism for cell polarity establishment. Phase separated droplets form small compartments in cells that organize biochemistry. Such biological condensates motivate the physical study of chemically active droplets that exhibit nonequilibrium states and that can imitate cell like behaviors such as spontaneous division. Active droplets can also serve as simple physical models of protocells that operate away from equilibrium. Finally, at larger scales, many cells organize collectively during the morphogenesis of organisms. These examples show that living matter is a form of active matter governed by nonequilibrium physics. To advance our understanding of principles that underlie the emergence of complex biological structures far form thermodynamic equilibrium will remain a challenge for future research.

Two-dimensional (2D) materials are atomically thin crystals characterized by strong in-plane chemical bonds and weak van der Waals (vdW) coupling between adjacent layers. This allows easy access to the crystals by exfoliation techniques such as the precedent “scotch-tape” tape methods. The weak coupling between the layers enables the combination of such 2D materials with other materials nearly without limitations e.g. towards wearables, flexible and bendable opto-/electronics and energy conversion applications. Atomically thin semiconducting transition metal dichalcogenides such as MoSe2 or WSe2 excel due to their strong exciton dominated light-matter interaction. Excitons are Coulomb-coupled electron-hole pairs and hence composite-bosons. The vdW nature allows the realization of precisely tailored 2D systems that can be engineered by stacking, precise twisting or by selectively inducing defects. In-situ control can be realized by external stimuli such as electric fields and charge doping in field effect structures.

Those VdW stacks can have properties individual layers or conventional 3D solids do not reveal: (i) twist-angle dependent moiré superstructure with periodic potential profiles and the formation of minibands [1] and (ii) momentum dependent hybridization of electronic state resulting in the competition between interlayer (IX) and intralayer (X) excitons [2,3]. In particular, we will discuss the low-temperature emission properties of dense interlayer exciton ensembles in MoSe2/WSe2 hetero-bilayers featuring several criticalities [4] and drastically reduced dipolar blueshift together with extended spatial coherence [5]. These findings are in agreement with the occurrence of a coherent many-body state of IX [5]. Moreover, we demonstrate that studying collective charge excitations between moiré-minibands in twisted WSe2 bilayers by means of resonant inelastic light scattering spectroscopy provide unique experimental access to the modulated bands in twisted bilayers structures [6].

[1] T. Deilmann et al., J. Phys.: Condens. Matter 32 333002 (2020).

[2] J. Kiemle et al., Phys. Rev. B 101, 121404(R) (2020).

[3] F. Sigger et al., Appl. Phys. Lett. 121, 071102 (2022).

[4] L. Sigl et al., Physical Review Research 2, 042044(R) (2020).

[5] M. Troue et al., Phys. Rev. Lett. 131, 036902 (2023).

[6] N. Saigal et al., in preparation.