Contributions to the Yearbook of the Max Planck Society

Whether or not crystal structures are mirror symmetric determines how their electrons behave. Researchers at the MPSD, working with an international team, have shown that, surprisingly, the electrons of the Kagome superconductor CsV₃Sb₅ display a chiral behaviour, despite their achiral crystal structure. An emergent electronic order breaks the mirror symmetry – a newly discovered phenomenon – and this order can be switched by magnetic fields. Such a switchable chirality could play an important role for future technologies.

In recent years, it has become possible to create short and strong laser pulses with many photons that interact with materials on extremely fast time scales and change the materials’ behavior. By contrast, in the adjacent research field of quantum optics, the quantum fluctuations of light take center stage, with only few virtual photons bubbling in and out of existence in the vacuum. At the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg we are now bridging these two fields and exploring the potential of both classical and quantum light to create designer materials with tailor-made properties that could enable new energy-saving and quantum-technology applications.

Just how has nature optimized certain biological structures to optimally transduce chemistry into living systems? In the area of barrier-crossing, which takes around 100 femtoseconds, there is a proposal that nature has optimized form and function to exploit quantum effects by environmental engineering to extend coherences - even electronic coherences - on the timescale relevant to electronic motions sensitive to the environment fluctuations. In enzymatic processes lasting microseconds and above, stochastic thermally driven motions need to steer the chemistry to drive biological functions.

Superconductors at very low temperatures show the remarkable property of being able to conduct electrical current without any resistance. However, the use of these materials in everyday life applications is severely limited by the need for cooling to at least minus 70 degrees Celsius. In carbon-based molecules, irradiation with intense mid-infrared laser light has now enabled to induce a short-lived transient superconducting state at higher temperatures. The knowledge gained might help in the development of materials that become superconducting at significantly higher temperatures.

The properties of matter, e.g., the conductivity, can be tailored with light. This can be done with a lot of photons that are part of a laser beam, or in certain cases only a few photons are enough. In the theory department of the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, researchers use both extreme cases to investigate novel states of matter: a laser allows theoretically generating hitherto unobserved states of matter and via a few photons chemical reactions can be altered.

Many processes in the chemistry of life take place on ultrashort length and time scales. Their observation thus lies beyond the capabilities of optical microscopes. The investigation of such processes using novel electron sources in many cases presents a cost-saving alternative to X-ray studies using synchrotron radiation sources and free-electron lasers. Also the development of methods for the preparation of liquid samples is essential for the study of many organic materials.

Superconductors carry an electric current without resistance only at low temperatures. Now, for the first time, scientists have turned a ceramic crystal into a superconductor even at room temperature, using an ultrashort mid-infrared flash of light. The superconducting state survived only for a couple of picoseconds (millionth of a microsecond), and the researchers found that this light-induced state is based on certain distortions of the material’s crystal lattice. These findings may aid the quest for higher temperature superconductors and pave the way for novel applications.