Using light to study the collective behavior of electrons Professor Tomasz Smoleński is a new member of the SNI network. Since the beginning of February 2025, he has been carrying out research as an assistant professor at the Department of Physics of the University of Basel as a successor to our former director, Professor Christian Schönenberger. Smoleński is passionate about studying the collective behavior of electrons in 2D materials. Together with his growing team, he investigates these phenomena using light, including with a view to applications in quantum technologies. The behavior of numerous electrons Quantum Opto-Electronics is the name of the group led by Tomasz Smoleński, the new assistant professor at Basel Universi- ty’s Department of Physics, who will also supervise a project at the SNI PhD School from 2026 onward. In simple terms, he and his team are investigating how large numbers of elec- trons behave in different phases and ma- terials. Smoleński compares this topic to a flock of birds moving in a complex pat- tern, unlike that of the individual bird. “The complex movement pattern arises not because each bird tracks the entire flock, but rather from simple rules — each bird merely responds to the behav- ior of its neighbors. A similar principle applies to electrons when many of them come together,” Smoleński explains. Electrons also exhibit collective be- havior that can be very complex — such as in a superconductor, which conducts electricity losslessly. However, this collec- tive behavior is often difficult to predict and calculate. Smoleński is therefore in- vestigating it using optical, noninvasive methods. Artificial materials with new properties Smoleński and his team use two-dimen- sional van der Waals heterostructures for their research. These structures consist of layers of atomically thin materials held together by weak van der Waals forces. This property enables different atomic layers to be combined in complex hetero- structures that can exhibit entirely new electronic properties. “Van der Waals heterostructures pro- vide us with an almost infinite number of new materials that offer an ideal plat- form for our investigations,” Smoleński explains. “One unique advantage of these materials is that they allow the number Network of electrons to be tuned in situ by apply- ing a voltage without having to change the material.” This tunability of their properties distinguishes the materials from others used in quantum science and is of great importance to the re- searchers. Investigations with light To study the properties of electrons in these heterostructures, Smoleński em- ploys various spectroscopic — that is, optical — methods that do not alter the material itself. In simple terms, he shines lasers onto layered structures hosting electronic phases and analyzes spectral properties of the reflected light that encode collec- tive properties of the electrons. By using a combination of optical methods, he can map the electronic states, also known as quantum phases, in terms of space, time and energy. Smoleński explains: “This 12 SNI INSight December 2025