12 March 2026
A new momentum microscope at Forschungszentrum Jülich makes electrons and their properties in solids visible. The instrument, developed entirely in Jülich, provides unprecedentedly insights into materials - and works significantly more effective than previous systems.
Electrons are tiny and constantly in motion. How they behave in a crystal lattice determines key material properties: electrical conductivity, magnetism, or novel quantum effects. Anyone aiming to develop the information technologies of tomorrow must understand what electrons do.
At Forschungszentrum Jülich, a new tool is now available for this purpose: a momentum microscope that was fully developed and built on site. "Internationally, we are currently seeing rapidly growing interest in this method," explains Dr. Christian Tusche from Forschungszentrum Jülich.
A pioneer of momentum microscopy
Dr. Christian Tusche already played a key role in advancing momentum microscopy during his time at the Max Planck Institute of Microstructure Physics in Halle. Since moving to Jülich in 2015, he has continued to drive its development forward. His work has been recognized with several awards, including the Kai Siegbahn Prize in 2018 and the Innovation Award on Synchrotron Radiation in 2016.
In recent years, numerous instruments have been commissioned at synchrotron facilities and X-ray laser around the world. Most recently, he published a review article on the method in the journal Applied Physics Letters.
"The new device we built together with the Mechanical Workshop is a real innovation. There is currently nothing like it available from any specialist company," says Dr. Tusche.
From large facilities to a UV laser
Until now, momentum microscopes typically required large-scale research facilities as radiation sources, such as electron accelerators or X-ray lasers. The Jülich system, by contrast, operates with a powerful tabletop UV laser.
This is made possible by a newly developed electron-optics design that is far more efficient than previous systems while delivering even sharper images of electron states.
From the photoelectric effect to the complete picture
Momentum microscopy is based on the photoelectric effect: when light strikes a material, electrons are emitted while retaining their momentum and often also their spin direction. From this information, it is possible to reconstruct the quantum state in which they previously existed. On this basis, photoemission spectroscopy and microscopy have become established techniques in solid-state physics.
"However, these methods reach their limits when it comes to capturing spin and momentum over wider energy ranges," explains Dr. Tusche. Momentum microscopy combines both approaches in a single instrument. "With just one or a few measurements, you can obtain the complete picture."
A map of electron motion
A momentum microscope not only shows where electrons are located, but also how they move. The measurements provide a kind of map of electron movement - with information on momentum, spin, orbitals, and spatial and temporal changes in a single experiment.
A simple analogy helps illustrate the concept: while a conventional microscope shows where people are standing in a marketplace, a momentum microscope reveals where they are heading and how fast they are moving - and in the case of electrons, also their spin orientation.
Electronic fingerprint
One of the key results is the so-called Fermi surface. It describes the momentum distribution of electrons and is crucial for determining the fundamental physical properties of a material.
Researchers use it like a fingerprint: the Fermi surface reveals whether the material is a metal or a semiconductor, or a quantum material with exotic effects such as superconductivity or complex magnetism.
A key to new discoveries
In the short time since its inception, momentum microscopy has already enabled numerous breakthroughs. Among other things, Christian Tusche's team succeeded in producing a two-dimensional semimetal that only conducts electrons with a specific spin direction - a promising approach for spintronics. In addition, the researchers observed a new effect for controlling the orbital angular momentum of electrons, which opens up prospects for future 'orbitronics'.
One device for many materials
The new Jülich microscope is suitable for a wide range of modern materials, including metals, ferromagnets, oxides, organic thin films, and topological quantum materials. Its electron lenses can be virtually shifted using variable electrical voltages. This allows researchers to zoom in on specific parts of the momentum images.
The use of a laser to excite the electrons in the sample also enables time-resolved experiments to be carried out, allowing ultra-fast processes to be investigated - for example, during the switching process of electronic devices.
A new window into the quantum world
And expectations go even further: "above all, we hope to encounter unknown effects that have not yet been seen," says Christian Tusche.
The Jülich momentum microscope is currently still in testing phase. A gold crystal serves as a reference for calibration. Soon, however, other materials will follow - opening up a new window into the quantum world.
Original publication
Momentum microscopy and its applications featured Open Access
Ying-Jiun Chen, Carsten Wiemann, Wei-Sheng Chiu, Christoph Schlueter, Claus M. Schneider, Christian Tusche
Appl. Phys. Lett. (2026), DOI: 10.1063/5.0304110
