The study described the class of metals based on their symmetry and a mathematical classification known as a topological number, which is predictive of special electronic properties.
"Topological classification is a very general way of looking at the properties of materials," said Princeton graduate student Lukas Muechler.
"The idea is that you don't really care about the details. As long as two materials have the same topological invariants, we can say they are topologically equivalent.”
While searching for superconductivity in a crystal of WTe2, a neighbouring lab instead found that the material could continually increase its resistance in response to magnetic fields.
The team extended the neighbouring labs’ research by considering the arrangement of the atoms in the crystal. While WTe2 is composed of many layers of atoms stacked upon each other, the team found that a single layer of atoms had a particular nonsymmorphic symmetry.
Having established the symmetry, the researchers mathematically characterised all possible electronic states having this symmetry, and classified those states that can be smoothly deformed into each other as topologically equivalent.
From this classification, they found WTe2 belongs to a new class of metals which they coined nonsymmorphic topological metals. These metals are characterised by a different electron number than the nonsymmorphic metals that have previously been studied.
In nonsymmorphic topological metals, the current-carrying electrons behave like relativistic particles. According to the team, this property is not as susceptible to impurities and defects as ordinary metals, making them attractive candidates for electronic devices.
"The silicon in modern devices has to be extremely pure and cristalline which requires complex fabrication methods," explained Muechler. "One could imagine that in future devices these fabrication procedures could be simplified due to the robustness of the electronic states in these new materials towards external factors.
"Materials such as WTe2 could be used as switches or sensors. With no external magentic field, the resistivity of the materials is low. If one applies a magnetic field, the resisistivity increases by several orders of magnitude. One could use these properties to define 'on' and 'off' signals, depending on the resistivity of the sample."
