How can new developments in nanotechnology be used to create quantum effects that have not yet been discovered? Physicist Fangyuan Yang, who conducts research at the Institute of Solid State Physics and in collaboration with the center for micro- and nanostructures (ZMNS) at TU Wien, investigates many-body phenomena and has set herself ambitious goals. She has now received the prestigious ASTRA Award from the Austrian Science Fund FWF. With funding of around half a million euros, she will establish her own research group at TU Wien.
Particle, wave or quasiparticle?
Quantum physics tells us that electrons cannot be imagined simply as tiny spheres. In some situations, they behave more like waves. In Fangyuan Yang’s research, however, the situation is even more complicated. She studies materials in which electrons strongly influence one another. They can no longer be described separately; instead, they must be considered as a collective system.
In such many-body systems, so-called “quasiparticles” can emerge: collective excitations involving many electrons. One can imagine this in a similar way to a wave moving through a football stadium: Each individual person in the stadium remains on their place, but the wave is a collective excitation that moves and is located at a particular place at a particular time. Specific properties can also be assigned to a quasiparticle, even though it is not a real particle, but rather a collective effect created by the interplay of many electrons.
A moiré effect in the crystal
Fangyuan Yang observes such effects in two-dimensional material layers – for example, in the 2D material graphene. A key trick in her work is that she combines two layers. However, they are not stacked in perfect alignment; instead, they are slightly twisted relative to each other. This creates a so-called moiré effect, similar to what can be seen optically when two grids are placed on top of each other and moved relative to one another. In this way, Fangyuan Yang creates a periodic potential that can be used to control the properties of the electrons, or of the quasiparticles they give rise to.
This makes it possible to study a wide range of effects. The fractional quantum Hall effect, for which the Nobel Prize in Physics was awarded in 1998, can normally only be observed in strong magnetic fields. With carefully designed layered materials, a very similar principle is expected to become measurable even without a magnetic field. Yang also aims to study new types of quantum phase transitions and investigate the topological properties of materials.
Fangyuan Yang
Fangyuan Yang completed her doctorate at Fudan University in Shanghai, China, in 2018. She then joined the University of California, Santa Barbara, USA, as a postdoctoral researcher. In 2023, she moved to the Institute of Solid State Physics at TU Wien, where she has since been studying many-body phenomena in two-dimensional materials. The ASTRA Award will now allow her to expand her research activities, hire doctoral students, and establish her young research group on the international stage.
Contact
Fangyuan Yang, PhD
Institute for Solid State Physics
TU Wien
+43 1 58801 138 760
fangyuan.yang@tuwien.ac.at