Fermi Surface Reconstruction and Anisotropic Linear Magnetoresistance in the Charge Density Wave Topological Semimetal TaTe4

TL;DR

This work addresses how CDW-induced Fermi-surface reconstruction in a topologically nontrivial, quasi-one-dimensional semimetal shapes bulk electronic structure and transport. By combining DFT with high-field magnetotransport in multiple configurations, the authors map the CDW-reconstructed FS, resolving four pockets and finding no evidence of non-CDW bands, while revealing a quasi-cylindrical pocket and a high-frequency magnetic-breakdown orbit that yields a CDW gap of about 0.29 eV. The study also reports robust linear magnetoresistance across field directions, with a second high-field linear regime likely tied to breakdown near hot spots, highlighting TaTe4 as a model system for the coexistence of correlation-driven band reconstruction and topological states. These findings advance understanding of how CDW order and topology interplay in bulk electronic structure and offer insights into magnetic breakdown phenomena in complex Fermi surfaces.”

Abstract

Understanding the interplay between topology and correlated electron states is central to the study of quantum materials. TaTe$_4$ is a quasi-one-dimensional charge density wave (CDW) compound predicted to host topological phases, which makes it a model platform to explore this interplay. Here, we combine high-field magnetotransport measurements with density functional theory calculations to provide a comprehensive mapping of the Fermi surface (FS) of TaTe$_4$ in its CDW phase. Using multiple current-field geometries, we resolve the four largest of six pockets of the FS predicted by theory and find no evidence of non-CDW bands, highlighting the full reconstruction of the FS in the bulk. We identify a previously unobserved quasi-cylindrical pocket and uncover a large size orbit consistent with magnetic breakdown between reconstructed FS sheets, from which we estimate a CDW gap of $\sim$0.29~eV. Moreover, we observe a robust linear magnetoresistance that persists across all field directions when current flows perpendicular to the 1D chains along which the CDW is formed, with a distinct high-field linear regime emerging when field is along the chains. These findings establish TaTe$_4$ as a prototypical material to study the coexistence of correlation-driven reconstruction and topological electronic states.

Figures (6)

• Figure 1: (Color online) (a) Unit cell of TaTe$_{4}$ in both the CDW (large rectangular prism) and non-CDW (small rectangular prism) phases. (b) High symmetry points of the first brillouin zone of TaTe$_{4}$, in both its high symmetry non-CDW phase (corners of red polygon with capital letters) and low symmetry CDW phase (corners of red polygon with lowercase letters). (c-d) and (e-f) are the band structure and Fermi surface of TaTe$_{4}$ obtained through DFT calculations for the non-CDW phase and the CDW phase, respectively. In (c,e) bands crossing the Fermi level are highlighted in colors other than black. (g) Four of the CDW FS pockets shown individually and in the corresponding band color of (e) to better illustrate the possible closed orbits for each. The other two FS pockets coming from bands in yellow and orange in (e), and centered around $a$ and $m$ points, are too small to be visualized.
• Figure 2: (Color online) Magnetoresistance curves for magnetic field at different rotation planes and current directions. From top to bottom: Row (a) corresponds to rotation of magnetic field within the a-a plane, with current along c (configuration A); row (b) corresponds to rotation of field within the a-c plane, with current along c (configuration B); and row (c) corresponds to the magnetic field rotation within the a-c plane, but with current along a (configuration C). From left to right: Column (i) for each row depicts the magnetic field and current setup for each case; column (ii) shows the symmetrized magnetoresistance data for all angles for each configuration as a function of magnetic field. The color scale represents the $\theta$ angle of orientation of the magnetic field with respect to the crystalline axis. For config. A an offset for each curve was added for better visualization of the plots; Column (iii) shows the oscillatory component of magnetoresistance curves as a function of the inverse of magnetic field; and column (iv) presents the fast Fourier transform of their corresponding curves in (iii), highlighting their dominant frequency composition and their evolution with field orientation.
• Figure 3: (Color online) Evolution of extremal areas ($i.e.$ frequencies) of pockets for different orientations of the magnetic field in configuration A. Rows (a), (b) and (c) correspond to high, mid, and low frequency regimes, respectively. Column (i) shows contour plots of the FFT in Fig. 2(a.iv) to highlight the evolution of frequencies as a function of the magnetic field orientation. Yellow color represents a high intensity, and dark blue represent zero intensity. Column (ii) shows the same contour plots now identifying the dominant frequency branches (solid dots), and comparing them with the DFT-predicted evolution of extremal areas of pockets (solid lines). Column (iii) shows the DFT pockets that explain the evolution of the observed frequencies. The color of each pocket is chosen to match the color of the dotted and solid lines in column (ii).
• Figure 4: (Color online) Evolution of extremal areas ($i.e.$ frequencies) of pockets for different orientations of the magnetic field in configuration C. Rows (a) and (b) correspond low/mid and high frequency regimes, respectively. Column (i) shows contour plots of the FFT in Fig. 2(c.iv) to highlight the evolution of frequencies as a function of the magnetic field orientation; Column (ii) shows the same contour plots now identifying the dominant frequency branches (solid dots), and comparing them with the DFT-predicted evolution of extremal areas of pockets (solid lines); Figures in (a)(iii) show the DFT pockets that explain the evolution of the observed frequencies, and the color of each pocket is chosen to match the color of the dotted and solid lines in the previous column. Figures in (b)(iii) show, in the left, the evolution of the amplitude of the FFT peaks associated to different frequencies (filled dots) as a function of the lower-cutoff field to perform the FFT. Solid lines represent fits to a $e^{-B_0/B}$ form. In the right, an schematic unfolding of the CDW bands into the non-CDW Brilloin zone is made, showing in green a putative magnetic breakdown orbit that could originate the $\sim$ 4 kT (at 90°) frequency seen in the data.
• Figure 5: (Color online) (a) Raw magnetoresistance data in configuration C as a function of magnetic field orientation, with an offset for each curve for better visualization. (b) Symmetrized non-oscillatory magnetoresistance data as a function of the magnetic field orientation (after removal of SdH oscillations). (c) Contour plot for the exponent $n(B,T)$ of the power law fit of the non-oscillatory magnetoresistance, obtained as explained in the text, as a function of both magnetic field orientation and the magnetic field intensity. (d) Symmetrized magnetoresistance data as a function of temperature for magnetic field oriented parallel to the c-axis. (e) Same as in (d), after removal of SdH oscillations to highlight the non-oscillatory component of MR. (f) Same as in (c), but as a function of temperature.