Topological insulators typically exist in crystalline materials, but there are still many theoretical predictions that need to be confirmed, said Professor Taylor Hughes. One such prediction is the existence of a topological insulator with a quadrupole moment, a so called QTI.
Researcher Wladimir Benalcazar noted: “We found that electrons in crystals can collectively to give rise not only to charge dipole units –pairings of positive and negative charges – but also high-order multipoles, in which four or eight charges are brought together into a unit. The simplest member of these higher-order classes is the quadrupole, in which two positive and two negative charges are coupled.”
The team built a workable-scale analogue of a QTI using a material created from PCBs. Each board holds a square of four identical resonators, with the boards arranged in a grid pattern to create the full crystal analogue.
“Each resonator behaves as an atom,” researcher Kitt Peterson explained, “and the connections between them behave as bonds between atoms. We apply microwave radiation to the system and measure how much is absorbed by each resonator. The more microwave radiation is absorbed by a resonator, the more likely it is to find an electron on the corresponding atom.
According to Peterson, the results pointed to the existence of predicted protected states that would be filled by electrons to form four corner charges and the team believes those corner charges be capable of storing data.
“That may not seem realistic using our ‘human scale’ model,” Prof Hughes said. “However, when we think of QTIs on the atomic scale, tremendous possibilities become apparent for devices that perform computation and information processing, possibly even at scales below that we can achieve today.”
