Low-frequency fluctuations in solids:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mfrac><mml:mrow><mml:mn>1</mml:mn></mml:mrow><mml:mrow><mml:mi>f</mml:mi></mml:mrow></mml:mfrac></mml:math>noise
An astonishing variety of systems show properties that fluctuate with approximately $\frac{1}{f}$-shaped spectral densities. In this review we deal with selected topics regardin...