A November 14 press release from Washington State University announced the accidental discovery of a 400-fold increase in the electrical conductivity of a crystal by exposing it to light. Researchers found that the effect lasted for several days after the crystal was removed from exposure to light, and promises to drastically improve the performance of electronic devices.
WSU doctoral student Marianne Tarun made the accidental discovery when she noticed that the conductivity of a strontium titanate crystal exploded after it was left out one day. She and her colleagues initially believed the sample was contaminated, but a succession of experiments showed the effect was, indeed, from light.
“It came by accident,” said Tarun. “It’s not something we expected. That makes it very exciting to share.”
Called “persistent photoconductivity” – not to be confused with superconductivity – the researchers achieved this phenomenon at room temperature, which makes it more practical than the extremely low temperatures required for superconductivity to occur. In addition, while other researchers have created persistent photoconductivity in other materials, the recent discovery is the most impressive display of the phenomenon.
The findings appear in this month’s issue of the journal Physical Review Letters.
“The discovery of this effect at room temperature opens up new possibilities for practical devices,” said Matthew McCluskey, coauthor of the paper and chair of WSU’s physics department. “In standard computer memory, information is stored on the surface of a computer chip or hard drive. A device using persistent photoconductivity, however, could store information throughout the entire volume of a crystal.”
This methodology, called holographic memory, “could lead to huge increases in information capacity,” McCluskey added.
Oxides like Strontium titanate contain oxygen and two or more other elements, and often display an incredible variety of electronic phenomena, from the high resistance used for insulation to the ultra-low resistance observed in superconductivity.
“These diverse properties provide a fascinating playground for scientists but applications so far have been limited,” said McCluskey.
McCluskey, Tarun and physicist Farida Selim, now a researcher at Bowling Green State University, exposed a sample of strontium titanate to light for 10 minutes, and found that its improved conductivity lasted for several days. The researchers hypothesize that the light frees electrons in the material, allowing the crystal to carry additional current loads.