Bulk Fermi surface of the layered superconductor TaSe3 with three-dimensional strong topological state

High-magnetic-field transport measurements and ab initio calculations on the layered superconductor TaSe3 have provided evidence for the existence of a three-dimensional strong topological state. Longitudinal magnetotransport measurements up to ∼33 T unveiled striking Shubnikov–de Haas oscillations with two fundamental frequencies at 100 and 175 T corresponding to a nontrivial hole Fermi pocket at the point and a nontrivial electron Fermi pocket at the B point, respectively, in the Brillouin zone. However, calculations revealed one more electron pocket at the B point which was not detected by the magnetotransport measurements, presumably due to the limited carrier momentum relaxation time. Angle-dependent quantum oscillations by rotating the sample with respect to the magnetic field revealed clear changes in the two fundamental frequencies, indicating anisotropic electronic Fermi pockets. The ab initio calculations gave the topological Z2 invariant of (1; 100) and revealed a single Dirac cone on the (1 0 −1) surface at the ¯X point with helical spin texture at a constant energy contour, suggesting a strong topological state. The results demonstrate TaSe3 as an excellent platform to study the interplay between the topological phase and superconductivity and a promising system for the exploration of topological superconductivity.