Goutam Sheet

Normally, electric current is the same in both directions, like water in a straight pipe. But at the boundary between a normal metal and a superconductor, this rule breaks down. Two waves on water, going around a wide obstacle from different sides, can arrive with different delays and meet ‘out of step’.

A metal needle descends onto a piece of superconductor. All of this happens inside a refrigerator that cools the sample to 30 thousandths of a degree above absolute zero — a hundred times colder than outer space. A weak current is passed through the needle, and by how electrons travel through the tiny contact point, physicists read what is happening inside the material.