Prof. Zhaorong Yang and Phys.org discussed the paper he and his colleagues published in Proceedings of the National Academy of Sciences, in which they report their discovery of the pressure-induced transition of the three-dimensional Dirac semimetal zirconium pentatelluride (ZrTe₅) to a superconductor by combining synchrotron X-ray diffraction, magnetic field low-temperature transport and theoretical investigations. "Three-dimensional Dirac semimetals are neighbor states to other exotic phases such as topological insulators, Dirac semimetals, Weyl semimetals, superconductors, and even topological superconductors," Yang tells Phys.org. "Recent theoretical and experimental studies show that ZrTe₅ is a very promising system that hosts topological properties and might help to pave a new way for further experimental studies of topological phase transitions." These discoveries spark the present team of scientists' interests to further investigations on its Dirac and topological characters in ZrTe₅ under high pressures, since pressure has proven to be an effective method for tuning electronic properties of materials by extensive studies.

Prof. Jian Sun (an author of the paper discussed in this article) notes that "The sample is small, experiments are performed under extreme conditions and the signals are not strong. So it is very difficult to determine the crystal structures of high pressure phases based on the experimental data only. Our theoretical crystal structure prediction technique provides us the best candidates under the experimental circumstances and can be compared with the measured signals to eventually nail down the real structures."

"We first conducted resistance and AC magnetic susceptibility measurements on ZrTe₅ single crystals at various pressures up to 68.5 gigapascals and observed two superconducting phases," Yang adds. One gigapascal (GPa) is equivalent to 1,000,000,000 pascals (Pa) – the standard unit of pressure defined as one newton per square meter. "However, we noticed that the constructed pressure-superconducting phase diagram is very similar to that of tellurium, possibly due to the decomposition of ZrTe₅ under high pressure." To determine the origin of this transition, the researchers carried out in situ high-pressure synchrotron X-ray diffraction and Raman spectroscopy measurements combined with theoretical calculations. "We're very lucky that both experimental measurements and theoretical calculations identified that the superconducting phases are coming from a two-stage structural phase transition."