First material found to "remember" its own history
Researchers at EPFL have discovered a material that seems to be able to “remember” all of its past encounters with stimuli, such as electrical currents. The compound could come in handy for better data storage and processing.
The material in question is vanadium dioxide (VO2), and it’s already known to have some intriguing properties. It’s normally an insulator, but when heated to 68 °C (154.4 °F) its lattice structure changes, meaning it acts like a metal instead. This can make it a great coating for windows or roofs that either block heat from the Sun or let it pass through, depending on the weather. Previous studies have even found that it can conduct electricity without conducting heat.
And now an EPFL team has added another strange feature to vanadium dioxide’s resume. The researchers were studying how quickly the material transitions between its insulating and conducting states, by applying an electric current to a sample of VO2. As expected, the current heated the material to its transition point, causing it to change, before settling back to its initial state after the current had passed.
But what happened next was unexpected. When a second current was applied, the speed at which the phase transition took place was different from that of the first current, suggesting the material had a kind of persistent “memory” of its history.
"The VO2 seemed to 'remember' the first phase transition and anticipate the next," said Professor Elison Matioli, corresponding author of the study. "We didn't expect to see this kind of memory effect, and it has nothing to do with electronic states but rather with the physical structure of the material. It's a novel discovery: no other material behaves in this way.”
In further experiments, the team found that VO2 could remember a previous stimulus for up to three hours. They suggested that the memory could even last a few days, but they didn’t have the proper instruments to measure it.
The researchers say that other materials could have the same ability, and finding them could lead to a new class of memory and data processing devices. Other materials have been known to exhibit a form of memory about their shape at different temperatures.
The research was published in the journal Nature Electronics.