Electrons in an ultra-clean gallium arsenide film behave like a crowd at a crossroads, where the tilt of the magnetic field sets the direction. At zero tilt, they form a compressible liquid of composite fermions, particles made of an electron and a pair of vortices. This state has no energy gap, so it is easy to destroy.
When the field is tilted to about 72°, a soft state appears with a tiny gap of about 30 millikelvins. The resistance drops to nearly zero. As the tilt increases to 75.3°, the gap closes and then reopens, but now as a rigid state. Its gap grows rapidly and reaches a plateau. Near the rigid state, a daughter state appears at filling 19/13.
The experiment showed that the tilt acts as a switch: it splits the Fermi contour, the boundary of occupied electron states, into two disconnected parts. This turns a single-component system into a two-component one and opens the way to two different quantum states. Today this is fundamental knowledge, but it could help in creating topological qubits for quantum computers.
The energy gap of the robust state at filling 3/2 grows so sharply with field that it saturates within just 0.8 T, which is comparable to the field change when tilting the sample by a couple of degrees.