The particle that is its own enemy
In 1937, the brilliant and reclusive Italian physicist Ettore Majorana proposed a strange new class of particle: a fermion that acts as its own antiparticle. Unlike an electron, which is annihilated in a burst of energy when it meets its antimatter twin, the positron, a Majorana fermion would be its own doppelgänger. For decades this remained a theoretical curiosity. Particle accelerators searched for them without success. Then, in 2012, a team at the Kavli Institute of Nanoscience at Delft University of Technology (TU Delft) announced they had found the signature of Majorana particles not as free-roaming entities, but as quasiparticles (emergent phenomena) at the ends of a tiny, specially constructed wire.
The experiment, led by Professor Leo Kouwenhoven, did not find a fundamental particle. Instead, it created the specific conditions under which the collective behavior of electrons mimics the properties of a Majorana fermion. The team fabricated a device from an indium antimonide (InSb) semiconductor nanowire. InSb is a material with strong spin-orbit coupling, a property required for the experiment. The nanowire was connected to a normal electrical contact (gold) at one end and a superconductor (niobium titanium nitride) at the other. When the device was cooled to cryogenic temperatures just above absolute zero and subjected to a magnetic field of around 100 millitesla, the team observed a peculiar electrical signal.