PhD defence: Local Noise Measurements to Probe Correlated, Disordered and Doped Materials

PLEASE NOTE: The candidate gives a layman's talk, therefore the livestream will start fifteen minutes earlier.

Many of the most remarkable properties of materials do not come from individual atoms or electrons, but from the way large numbers of them work together. This phenomenon, known as emergence, lies at the heart of modern condensed matter physics. Superconductivity (the ability of certain materials to conduct electricity without resistance) is one of the most striking examples. Despite decades of research, many questions remain about how superconductivity arises in complex quantum materials and how it is affected by disorder, impurities, and electronic interactions.

In this thesis, I explore these questions by looking at materials on the scale of individual atoms using a technique called scanning tunneling microscopy (STM). STM allows us to map the electronic landscape of a material with atomic precision. But instead of only measuring the average electrical current, this work focuses on something that is usually considered undesirable in experiments: electrical noise. These tiny fluctuations in the current contain hidden information about how electrons move, interact, and organise themselves.

To access this information, I developed an extremely sensitive measurement system capable of detecting extremely small electronic signals at very low temperatures. Using this approach, I investigated high-temperature superconductors, disordered superconducting materials, and doped semiconductors. The measurements reveal how electrons can begin to form pairs before superconductivity fully develops, how microscopic defects influence superconducting behaviour, and how individual impurities can rapidly switch between different charge states.