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

Abstract

High magnetic field transport measurements and ab initio calculations on the layered superconductor TaSe 3 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 Γ point respectively in the Brillouin zone. However, calculations revealed one more electron 2 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 Z 2 invariants of (1; 100) and revealed a single Dirac cone on the (1 0 -1) surface at the point with helical spin texture at a constant-energy contour, suggesting a strong topological insulator state. The results demonstrate TaSe 3 an excellent platform to study the interplay between topological phase and superconductivity and a promising system for the exploration of topological superconductivity. † The authors contributed equally to this work.

Observation of Topological Electronic Structure in Quasi-1D Superconductor TaSe3

“…Two main peaks with frequencies of F 1 = 84 G 8 T and F 2 = 180 G 9 T were deduced Article by fast Fourier transformation (FFT) (see Supplemental Experimental Procedures, part II), indicating the existence of two Fermi surface (FS) pockets with area of 0.008 G 0.001 A ˚À2 and 0.017 G 0.001 A ˚À2 , in line with recent reports. 41,42 Since the prismatic Ta-Se chains have strong bonding along the a and b axes but relatively weak bonding along the c axis, the compound is easily cleaved along the ½101 direction, as previously illustrated in Figure 1B. The morphology of the cleaved surface was investigated by STM measurement.…”

“…In addition, in the monolayer limit, 39 a quantum spin Hall insulator phase is expected so that the topological edge state is expected to form a 1D TSC (see Supplemental Experimental Procedures part I, and Guille ´n et al 40 ). Furthermore, TaSe 3 contains many other intriguing physical properties such as large non-saturating magneto-resistance, 41,42 charge density wave in mesowires, 43 high current-carrying capacity, 44,45 and low levels of noise spectral density, 46 making it an important platform from which to study the nature of TSCs as well as possible applications such as interconnects in quantum computers. 44,45 Despite the strong motivations, the experimental confirmation of the topological electronic structure of TaSe 3 is challenging.…”

“…44,45 Despite the strong motivations, the experimental confirmation of the topological electronic structure of TaSe 3 is challenging. Although there have been various indications (e.g., the magnetic torque oscillation measurements have revealed the topological effects of the superconducting vortex state in a TaSe 3 ring crystal, 47 and the Shubnikov-de Haas (SdH) quantum oscillation reveals a non-trivial Berry phase 41 ), a direct observation of the TSSs is lacking.…”

“…High-quality single crystals of TaSe 3 were grown from a self-flux method as described by Xia et al 41 Starting materials of Ta powder (99.9%, Aladdin) and Se (99.999%, Aladdin) granules were mixed in a molar ratio of 1:6 and placed into an alumina crucible. The assembly was heated in a furnace up to 750 C within 9 h and kept for 20 h, then slowly cooled down to 450 C at a temperature-decreasing rate of 1.5 C/h.…”

Nontrivial topological states in the tantalum dipnictides TaX2 (X = As, P)

“…As an effective method to probe the shape of Fermi surface (FS), quantum oscillations of the MR, namely, Shubnikov-de Haas (SdH) oscillations, or magnetizations, namely de Haas-van Alphen (dHvA) oscillations, have been widely used in the past decades [38][39][40][41][42][43]. Through the analysis of the quantum oscillations, it is helpful for mapping out of the FS and is informative of the topological nature of the electronic band structure.…”