Physics

Prof. Jens Mueller
Institute of Physics, Goethe-University Frankfurt, Germany

Electronic noise, on the one hand, is mostly considered an unwanted nuisance and is sought to be reduced or even eliminated, since it ultimately limits the accuracy of physical measurements. On the other hand, understanding the microscopic origin of the different noise sources in condensed matter systems may help to improve the signal-to noise ratio and therefore the performance of semiconductor sensors and devices. Another point of view, however, is to consider “noise as the signal”, since the frequency-dependent fluctuations are related to the autocorrelation function of the measured quantity. Therefore, fluctuation spectroscopy is a powerful tool for studying the microscopic kinetics of charge carriers in condensed matter systems. In this talk, we will discuss how resistance fluctuations, in particular 1/f- and random-telegraph noise, reveal ‘hidden’ pieces of information on the low-frequency dynamics of charge carriers in solids, not present in the mean quantity (the resistance) itself. We will give an overview of recent noise studies on a variety of different systems and phenomena ranging from switching dynamics in micro- and nano-scale semiconductor heterostructure devices (thereby enabling high-resolution nanoscale magnetic measurements) to glassy structural dynamics in molecular metals. In these materials, we will discuss in some detail the low-frequency dynamics of strongly correlated electrons, namely recent findings of nano-scale electronic phase separation and critical slowing down of the order parameter fluctuations at the Mott metal-insulator transition, a key phenomenon in modern condensed-matter physics. We will describe a phenomenological model for the ubiquitous 1/f noise and its relation to a well-defined distribution of activation energies of two-level processes. If time allows, another prominent example to be mentioned is the percolation of magnetic polarons in materials exhibiting colossal magnetoresistance.