Andreev bound states

Andreev bound states are special energy levels that form inside a superconductor when it interfaces with a normal metal or other materials. At this boundary, electrons reflect as holes, creating a process called Andreev reflection. This leads to the formation of these states, which are confined near the interface and allow supercurrents to flow smoothly even through tiny gaps or obstacles. They play a crucial role in understanding superconductivity's quantum behavior, especially in nanostructures and quantum devices, by enabling current to pass without resistance at specific energies defined by these bound states.