In a crystal made of europium, zinc, and phosphorus, electric current behaves like a car on a bumpy road. Electrons don't run freely but drag magnetic clouds, polarons, behind them. At room temperature, these clouds are scattered, but when cooled, they merge into a continuous mass, causing the current to slow down dramatically.
Measurements at terahertz frequencies (trillions of oscillations per second) showed that the material's resistance changes more than with direct current. At a frequency of 1.5 terahertz, the resistance increased almost twofold compared to zero frequency. It's as if the road became increasingly bumpy specifically for fast oscillations.
Such behavior opens the way to devices where a magnetic field controls current at ultrahigh frequencies. For example, for creating switches in future terahertz electronics, which work faster than today's.
The crystal's resistance changes three times more at terahertz frequencies than with ordinary direct current.
In Arthur C. Clarke's novel "The City and the Stars," computers use crystals with unusual properties for ultra-fast calculations — similar to how magnetic polarons might control current in new devices.