Magnetic impurities in superconductors
Superconductors are special materials that carry electricity without energy loss. However, even the smallest magnetic impurities can interfere with this property, creating local disruptions. At the quantum level, tiny disruptions called YSR (Yu-Shiba-Rusinov) excitations happen when magnetic atoms interact with a superconductor. These excitations are like small signals showing how the magnetic properties of the atoms disturb the smooth, coordinated flow of electrons in a superconductor. By studying these signals, scientists can better understand the delicate balance between magnetism and superconductivity. “Understanding these interactions is essential for designing better superconducting materials”, the researchers explain.
New experimental approach
To study these interactions, the team designed a unique experimental platform. They placed magnetic molecules (manganese phthalocyanine, or MnPc) on an ultrathin layer of lead, a superconducting material. When lead is made extremely thin, it remains superconducting even in strong magnetic fields, provided the field is applied parallel to its surface. The experiments were possible because of the unique infrastructure that exists in the STILL labs. There, using a powerful microscope at temperatures close to absolute zero, the researchers studied YSR excitations while applying magnetic fields up to 4 Tesla.
The team found two different types of YSR excitations. The first type followed simple patterns that matched well with the current theories, meaning scientists already understood how these interactions worked. However, the second type was more complicated, involving multiple magnetic centers in the molecule interacting at once. This complexity did not fit neatly with existing theories, leaving gaps in our understanding and sparking new questions about how high-spin magnetic systems—those with stronger magnetic properties—affect superconductors and behave at the quantum level. “I am very pleased with these awesome results, as they give insight into the fundamentals of the applications of tomorrow”, researcher Niels van Mullekom says.
Scanning Probe Microscopy
Niels van Mullkom is PhD candidate in the Scanning Probe Microscopy group, which is led by Professor Alex Khajetoorians. The research group is part of IMM. Their research focuses on understanding new phases of matter, understanding how molecular interactions lead to macroscopic properties and studying structural, electronic, and magnetic properties of surfaces. In their approach to tackle these challenges in physics and chemistry, they make use of state-of-the-art methods in scanning probe microscopy (SPM).