We often learn that electricity arises from the movement of electrons through a metal. Each electron carries a discrete, quantized charge. However, this simple picture becomes more complex because electrons naturally repel one another. When a single electron moves, it can disturb the surrounding cloud of neighboring electrons.
When these disturbances are relatively small, electrons no longer move individually but instead behave collectively, forming groups known as electron quasiparticles. Despite this grouping, electrical current is still carried by discrete charges. However, these charges are no longer isolated “free” electrons but are manifestations of collective electron motion. This behavior is described by Fermi liquid theory, which has served as the standard framework for understanding metals for more than sixty years.
Surprisingly, many newly discovered materials, referred to as “strange metals,” do not conform to this traditional model. In these materials, electrical conduction is not carried by discrete electron-like charges. Using a technique called shot noise measurement, researchers have observed that electrons in strange metals blur into a continuous, featureless quantum fluid.
This raises a profound question: if individual electrons are not carrying the current, what is? Fermi liquid theory represents one of the major achievements of condensed matter physics, which is the branch of physics devoted to the study of solid materials. The discovery of strange metals challenges a cornerstone of our understanding. Developing a new theory to explain electrical transport in these unusual materials could lead to transformative insights across physics and materials science.
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