Memristors are a "thin titanium dioxide film held between two metal electrodes, and they act within circuitry as resistors. However, memristors have the added quality of remembering the resistance they had when current last flowed through them, hence the portmanteau name. Their resistance increases or decreases depending on the direction of the current," according to ZDNet UK's David Meyer.

"Representing a fourth basic passive circuit element, memristors have the ability to ‘remember’ the total electrical charge that passes through them," says Research associate John Paul
Strachan.

Electrical charge flowing through a memristor changes the resistance state of the device, but actually observing the corresponding material changes has been a challenge. Highly focused x-rays were used to probe the memristor non-destructively and a ~100 nm region with concentrated oxygen vacancies (right, shown in blue) where the memristive switching occurs was discovered. Surrounding this region a newly developed structural phase (red) was also found, which acted like a thermometer telling researchers where and how hot it became.

Caption credit: HP