Concurrence of superconductivity and structure transition in Weyl semimetal TaP under pressure

Weyl semimetal defines a material with three-dimensional Dirac cones, which appear in pair due to the breaking of spatial inversion or time reversal symmetry. Superconductivity is the state of quantum condensation of paired electrons. Turning a Weyl semimetal into superconducting state is very important in having some unprecedented discoveries. In this work, by doing resistive measurements on a recently recognized Weyl semimetal TaP under pressures up to about 100 GPa, we show the concurrence of superconductivity and a structure transition at about 70 GPa. It is found that the superconductivity becomes more pronounced when decreasing pressure and retains when the pressure is completely released. High-pressure x-ray diffraction measurements also confirm the structure phase transition from I 4 1 md to P -6 m 2 at about 70 GPa. More importantly, ab-initial calculations reveal that the P -6 m 2 phase is a new Weyl semimetal phase and has only one set of Weyl points at the same energy level. Our discovery of superconductivity in TaP by high pressure will stimulate investigations on superconductivity and Majorana fermions in Weyl semimetals. Topological semimetals: Superconductivity under pressure Under pressure, Weyl semimetals can become superconductive; in TaP, the superconducting transition is associated with a phase transition. Weyl semimetals are topological materials hosting massless quasiparticles, the Weyl fermions. A team of researchers led by Hai-Hu Wen at Nanjing University, in collaboration with colleagues from other Chinese institutes and the US, investigated the effect of applying high pressures to tantalum phosphide, discovering that the material undergoes a structural phase transition under pressure, becoming superconductive. Theoretical calculations and x-ray diffraction measurements clarify the structure of the new phase. Interestingly, the superconductive behaviour becomes more pronounced as the pressure is decreased, and the sample remains superconductive after the pressure is released. Inducing superconductivity in Weyl semimetals is interesting because it can result in the observation of exotic phenomena, such as the appearance of Majorana fermions.