Role of spin-orbit coupling and evolution of the electronic structure ofWTe2under an external magnetic field

Abstract

Here, we present a detailed study on the temperature and angular dependence of the Shubnikovde-Haas (SdH) effect in the semi-metal WTe2. This compound was recently shown to display a very large non-saturating magnetoresistance which was attributed to nearly perfectly compensated densities of electrons and holes. We observe four fundamental SdH frequencies and attribute them to spin-orbit split, electron-and hole-like, Fermi surface (FS) cross-sectional areas. Their angular dependence seems consistent with ellipsoidal FSs with volumes suggesting a modest excess in the density of electrons with respect to that of the holes. We show that density functional theory (DFT) calculations fail to correctly describe the FSs of WTe2. When their cross-sectional areas are adjusted to reflect the experimental data, the resulting volumes of the electron/hole FSs obtained from the DFT calculations would imply a pronounced imbalance between the densities of electrons and holes. We find evidence for field-dependent Fermi surface cross-sectional areas by fitting the oscillatory component superimposed onto the magnetoresistivity signal to several Lifshitz-Kosevich components. We also observe a pronounced field-induced renormalization of the effective masses. Taken together, our observations suggest that the electronic structure of WTe2 evolves with the magnetic field due to the Zeeman splitting. This evolution is likely to contribute to its pronounced magnetoresistivity.

Thickness-dependent electronic structure in WTe2 thin films

“…This is in contrast to the angle dependence of bulk samples, which follows the ellipsoidal model of 3D electronic systems [3,11]. This is also different from the 30-nm sample (S70) in Fig.…”

“…Four main frequencies, F 1 , F 2 , F 3 , and F 4 , can be resolved from thin-film samples, as shown in a typical fast Fourier transform (FFT) spectrum in the inset of Fig. 2(b) (for a detailed description of the method we used to trace the four frequencies at different angles, see Appendix A), and agree with the four fundamental frequencies in the high-mobility bulk samples [3,4,11].…”

“…• [3,11]. Therefore, the angle-dependent measurements indicate the WTe 2 thin-film samples with t 20 nm are in the 2D regime, and the thin-film sample with a thickness of 30 nm is more electronically 3D-like.…”

“…θ is the tilt angle between the normal of the sample surface and the magnetic field direction. Since WTe 2 has multiple Fermi surfaces [3][4][5]11], to illustrate the detailed structure of each Fermi surface, the SdH oscillations have been fast Fourier transformed to resolve corresponding oscillation frequencies. Four main frequencies, F 1 , F 2 , F 3 , and F 4 , can be resolved from thin-film samples, as shown in a typical fast Fourier transform (FFT) spectrum in the inset of Fig.…”

“…It is believed that the peculiar magnetoresistance occurs due to the nearly equal electron and hole concentrations with high carrier mobility [1][2][3][4][5][6][7][8], and forbidden backscattering due to strong spin-orbit coupling also plays an important role [9]. Surprisingly, although WTe 2 is a layered material, the anisotropy of the effective mass is small [10], and quantum oscillations can be observed along three different crystal axes [3,11], which makes it essentially a three-dimensional (3D) instead of two-dimensional (2D) electronic system [12].…”