Washington State University student discovers crystal’s light-sensitivity

An accidental discovery at a Washington State University research lab could have large implications for how we store digital information in the future.

WSU doctoral student Marianne Tarun and other researchers in the physics department have recently published their findings regarding a phenomenon known as persistent photoconductivity in the journal Physical Review Letters. Their research stemmed from an accidental discovery Tarun made about a year ago.

Tarun said she was studying how imperfections in crystals and other semiconductor materials affect electrical conductivity. Then one day, a type of crystal known as strontium titanate was left out in the lab and exposed to the room’s light.

Tarun analyzed the crystal’s conductivity later and found it had increased 400-fold. Furthermore, the heightened levels of conductivity occurred at room temperature and lasted several days after the light was turned off. That’s known as persistent photoconductivity, she said.

She said scientists have studied this phenomenon on other materials, but none have reached this level of conductivity.

Thinking the crystal may have been contaminated, she ran experiments on it. Tarun said she exposed it to different colors of light – including red, blue and green light – all of which yielded no results. However, Tarun said when she exposed it to violet light, the same color of light emanating from the fluorescent lights in the lab, the conductivity “dramatically” increased.

“I never thought room light would have an effect on my sample,” she said.

She said exposure to light excited the electrons, causing them to move and create electrical conductivity.

Matthew McCluskey, a physics professor working with Tarun, said there’s potential to use this type of conductivity to store digital information, and lots of it. He said memory in computers is currently stored in the silicon – another crystal – on the surface of microchips. A crystal like strontium titanate that can hold high levels of current for extended periods of time at room temperature opens up new possibilities.