[Paper Review] Anisotropic Fermi surface probed by the de Haas-van Alphen oscillation in proposed Dirac Semimetal TaSb$_{2}$

Arnab Pariari, Ratnadwip Singha+3 more|arXiv (Cornell University)|Jun 9, 2017

Topological Materials and Phenomena31 references3 citations

TL;DR

This study uses de Haas-van Alphen (dHvA) oscillations in TaSb₂ single crystals to probe the anisotropic Fermi surface, revealing three electron-type Fermi pockets with distinct cross-sectional areas when the magnetic field is rotated along different crystallographic directions. The anisotropy in magnetoresistance is attributed to differences in quasi-particle scattering time, with magnetoresistance decreasing from ~20,000% to ~9,500% as the field is rotated from 75° to 165°, confirming strong directional dependence in electronic transport.

ABSTRACT

TaSb$_{2}$ has been predicted theoretically and proposed through magnetotransport experiment to be a topological semimetal. In earlier reports, the Shubnikov-de Haas oscillation has been analyzed to probe the Fermi surface, with magnetic field along a particular crystallographic axis only. By employing a sample rotator, we reveal highly anisotropic transverse magnetoresistance by rotating the magnetic field along different crystallographic directions. To probe the anisotropy in the Fermi surface, we have performed magnetization measurements and detected strong de Haas-van Alphen (dHvA) oscillations for the magnetic field applied along extbf{b} and extbf{c} axes as well as perpendicular to extbf{bc} plane of the crystals. Three Fermi pockets have been identified by analyzing the dHvA oscillations. Hall measurement reveals electron as the only charge carrier, i.e., all the three Fermi pockets are electron type. With the application of magnetic field along different crystal directions, the cross sectional areas of the Fermi pockets have been found significantly different. Other physical parameters, such as the effective mass of the charge carrier and Fermi velocity have also been calculated using the Lifshitz-Kosevich formula.

Motivation & Objective

• To investigate the anisotropic Fermi surface in TaSb₂, a proposed Dirac semimetal, using quantum oscillation measurements.
• To determine the directional dependence of magnetoresistance and link it to Fermi surface geometry.
• To identify and characterize multiple Fermi pockets through de Haas-van Alphen oscillations along different crystallographic axes.
• To clarify the role of scattering time and effective mass anisotropy in explaining transverse magnetoresistance anisotropy.
• To provide unambiguous evidence for the topological nature of TaSb₂ by resolving Fermi surface anisotropy beyond previous single-axis measurements.

Proposed method

• Conducted magnetization measurements with magnetic field rotated along the b, c, and (c×b) crystallographic directions to probe Fermi surface anisotropy.
• Performed de Haas-van Alphen (dHvA) oscillation analysis to extract Fermi surface cross-sectional areas, effective masses, and Fermi velocities.
• Applied the Lifshitz-Kosevich formula to fit thermal damping of oscillations and extract physical parameters such as effective mass and Fermi velocity.
• Used fast Fourier transformation (FFT) of dHvA data to identify three distinct oscillation frequencies corresponding to three Fermi pockets.
• Measured transverse magnetoresistance at 2 K under varying field orientations to correlate anisotropy with Fermi surface geometry.
• Conducted Hall measurements to confirm electron-type carriers across all Fermi pockets.

Experimental results

Research questions

• RQ1 How does the Fermi surface of TaSb₂ vary with the orientation of the applied magnetic field?
• RQ2 What causes the observed large anisotropy in transverse magnetoresistance in TaSb₂?
• RQ3 Are there multiple Fermi pockets in TaSb₂, and how do their cross-sectional areas differ along different crystallographic directions?
• RQ4 To what extent does the quasi-particle scattering time contribute to the anisotropy in magnetoresistance?
• RQ5 Can dHvA oscillations unambiguously resolve the Fermi surface topology in TaSb₂, especially in the context of its proposed Dirac semimetal behavior?

Key findings

• Three distinct Fermi pockets were identified via dHvA oscillations, with oscillation frequencies of 372 T, 417 T, and 454 T when the magnetic field was applied along the c-axis.
• The Fermi surface cross-sectional areas for the three pockets were found to be comparable, with values of 35.2, 39.3, and 51.4 ×10⁻² Å⁻², respectively.
• The effective mass of the charge carriers was calculated as 0.31 m₀ for the dominant peak at 372 T, with Fermi velocity of 3.9×10⁵ m/s.
• Transverse magnetoresistance decreased from ~20,000% at 9 T and 2 K in the θ = 75° configuration to ~9,500% at θ = 165°, indicating strong anisotropy.
• The anisotropy in magnetoresistance is primarily attributed to differences in quasi-particle scattering time, with longer τ in the (c×b) direction due to smaller Fermi surface cross-section.
• Hall measurements confirmed that all three Fermi pockets are electron-type, supporting the electron-doped nature of TaSb₂.