Enter the Majorana Fermion

摘要

All known fundamental particles are either bosons or fermions. Fermi-ons are subject to the Pauli principle, which forbids two particles being in the same quantum state; bosons, by contrast, tend to bunch together in the same state. The same rule applies to the excitations of most solid-state systems, such as metals and semiconductors, which can be classified as fermi-onic or bosonic. However, sometimes excitations—quasiparticles—of a fundamentally different type emerge that resemble particles that hitherto have been considered only as a mathematical possibility. On page 1003 of this issue, Mourik et al. (1) report on a superconducting nanostructure that harbors such an exotic quasiparticle, a "Majorana bound state," an excitation that can best be described as half a fermion. The Majorana bound state is named after the Italian physicist Ettore Majorana, who proposed an equation describing a fermionic particle with a real-valued wave function (2).