  High magnetic field transport measurements and ab initio calculations on the
layered superconductor TaSe3 have provided compelling evidences for the
existence of a three-dimensional strong topological insulator state.
Longitudinal magnetotransport measurements up to ~ 33 T unveiled striking
Shubnikov-de Hass oscillations with two fundamental frequencies at 100 T and
175 T corresponding to a nontrivial electron Fermi pocket at the B point and a
nontrivial hole Fermi pocket at the {\Gamma} 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 invariants 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 insulator state. The results
demonstrate TaSe3 an excellent platform to study the interplay between
topological phase and superconductivity and a promising system for the
exploration of topological superconductivity.
