Pressure-induced superconductivity in topological semimetal NbAs2

Topological superconductivity with Majorana bound states, which are critical to implement nonabelian quantum computation, may be realized in three-dimensional semimetals with nontrivial topological feature, when superconducting transition occurs in the bulk. Here, we report pressure-induced superconductivity in a transition-metal dipnictide NbAs2. The emergence of superconductivity is not accompanied by any structural phase transition up to the maximum experimental pressure of 29.8 GPa, as supported by pressure-dependent synchrotron X-ray diffraction and Raman spectroscopy. Intriguingly, the Raman study reveals rapid phonon mode hardening and broadening above 10 GPa, in coincident with the superconducting transition. Using first-principle calculations, we determine Fermi surface change induced by pressure, which steadily increases the density of states without breaking the electron–hole compensation. Noticeably, the main hole pocket of NbAs2 encloses one time-reversal-invariant momenta of the monoclinic lattice, suggesting NbAs2 as a candidate of topological superconductors. Superconductivity is observed in NbAs2, indicating that this predicted topological material could host Majorana fermions. Using transport measurements, researchers led by Zhu-An Xu from Zhejiang University and Zhaorong Yang from the National High Magnetic field Laboratory in Hefei have demonstrated a superconducting transition when this compound is placed under high pressure. X-ray diffraction shows that no structural transition accompanies the onset of superconductivity, but Raman scattering and density functional theory calculations suggest that the pressure induces changes in the electron–phonon coupling and electronic density of states that facilitate the superconductivity. The band structure of NbAs2 is predicted to host topological features, indicating that transition metal dipnictides such as this could be time reversal invariant topological superconductors, and may feature Majorana edge modes that can be utilized in fault-tolerant quantum computing.