Electrons in materials can behave in strikingly different ways than their free counterparts. Especially at cold temperatures, interactions between electrons and atoms in a material make the whole system act more like it’s composed of free particles that have different masses and possibly different electric charge and spin from electrons. These are known as quasiparticles, and their properties give rise to all sorts of interesting phenomena, from superconductivity to bizarre magnetic behavior to emulation of high-energy particle physics. My latest piece for Nautilus has the story:

Many materials exhibit quasiparticle behavior that’s perfectly common but seems weird from our everyday world of classical physics. Some materials have quasiparticles that act like they have negative mass, and which are produced by the absence of electrons in its usual places. Those are known as “holes”, and rather than think of them as negative charges with negative mass, physicists treat them as positive charges with positive mass (since the physical effect is the same). Many semiconductors—ubiquitous in modern electronics—carry current primarily via holes. [Read more….]