According to the team, only two other TDS materials are known to exist and alpha-tin is currently its only simple-element member.
TDSs is said to exhibit electronic properties on their surfaces, akin to those of topological insulators (TIs). The surfaces of TIs allow electrons to conduct freely like a metal, while the interior behaves as an insulator.
"TDSs are of interest because they exhibit a number of novel physical properties, including ultrahigh carrier mobility, giant linear magnetoresistance, chiral anomaly, and novel quantum oscillations,” said physics graduate student Caizhi Xu.
“Secondly, this class of materials can realise many interesting topological phases – under controlled conditions, the material can undergo phase transitions and can become a topological insulator, a Weyl semimetal, or a topological superconductor."
In the experiment, the team engineered a strain on the material by growing alpha-tin samples in layers on a substrate of indium antimonide, which has a slightly different lattice constant.
"That lattice mismatch leads to strain, or compression, in the alpha-tin," Xu explained. "It was believed that strain would open a band gap in grey tin and turn it into a TI.
“I found that alpha-tin under a compressive strain is not an insulator, but a Dirac semimetal. Our calculations also show that it is only under a tensile strain that alpha-tin becomes a TI.
According to Xu, the semimetal’s high carrier mobility could generate ultrafast electronic devices and its magnetoresistance could be useful in developing ultra-compact storage devices, including computer hard disks.