Phonon-limited carrier transport in the Weyl semimetal TaAs

Abstract

Topological Weyl semimetals represent a novel class of quantum materials that exhibit remarkable properties arising from their unique electronic structure. In this work, we employ state-of-the-art ab initio methods to investigate the role of the electron-phonon interactions on the charge transport properties of TaAs. Our calculations of the temperature-dependent electrical conductivity with the iterative Boltzmann transport equation show excellent agreement with experimental measurements above 100 K. Extending the analysis to doped systems, we demonstrate that even small shifts in the Fermi level can lead to substantial changes in conductivity, driven by the complex topology of the Fermi surface. In particular, modifications in Fermi surface nesting emerge as a key factor influencing scattering processes and carrier lifetimes. These findings offer critical insights into the microscopic mechanisms that govern transport in TaAs and highlight the sensitivity of Weyl semimetals to doping and carrier dynamics.

Figures (5)

• Figure 1: (a) Crystal structure of TaAs, with Ta and As atoms shown as brown and green spheres, respectively. (b) Electronic band structure with orbital-resolved (fat band) character, along with total and partial density of states (DOS). (c) Brillouin zone with the $k_x=0$ and $k_y=0$ mirror planes showing the 12 pairs of Weyl nodes. The two distinct types of Weyl nodes, W1 and W2, are indicated by red and blue colors, respectively. Solid spheres and open diamonds represent the opposite chirality of the Weyl points. (d) Zoomed-in view of the band structure highlighting the Weyl nodes W1 located approximately 8.5 meV below the Fermi level and the Weyl nodes W2 located approximately 2.5 meV above it. The $a_0$ in the $x$-axis label denotes the unit cell edge length, given by $\sqrt{2a^2+c^2}/2$.
• Figure 2: Phonon dispersion of TaAs with (a) mode-resolved electron-phonon coupling strength $|g_{\mathbf{q} \nu}|$ and (b) phonon linewidths $\gamma_{\mathbf{q} \nu}$ indicated by a color scale. The total and atom-projected phonon density of states (PhDOS) are shown alongside panel (a). Hollow black circles in the phonon dispersion in panel (a) correspond to Raman data from Ref. Liu2015. (c) Fermi surface generated using a 10 meV energy window around the Fermi level with the XCrySDen package Kokalj1999. The surface reveals eight banana-shaped hole pockets, each containing a pair of W2 nodes. The black solid arrows indicate possible inter-pocket scatterings with $\mathbf{q}_1$ and $\mathbf{q}_2$ wave vectors along the $\Gamma$-$Z$ and $\Gamma$-$X$ directions (dashed lines), respectively. (d) Nesting function shown along the same high-symmetry path as in panels (a) and (b). The two peaks along the $\Gamma$-$Z$ and $\Gamma$-$X$ directions are labeled by wave vectors $\mathbf{q}_{1}$ and $\mathbf{q}_{2}$.
• Figure 3: (a) Electrical conductivity and (b) resistivity of TaAs for the undoped system ($\varepsilon_{\rm F}=\varepsilon_{\rm F}^0$) and for two levels of electron and hole doping ($\varepsilon_{\rm F} = \varepsilon_{\rm F}^0 \pm 25$ meV and $\varepsilon_{\rm F} = \varepsilon_{\rm F}^0 \pm 10$ meV). Experimental data from Refs. Huang2015 and Zhang2017 are shown as hollow symbols for comparison. The three highest quality samples, labeled as S1, D11, and D1 in Ref. Zhang2017, are used.
• Figure 4: (a) Three dimensional Fermi surface, (b) nesting function, and (c) scattering rates for hole-doped ($\varepsilon_{\rm F} = \varepsilon_{\rm F}^0-25$ meV) and electron-doped ($\varepsilon_{\rm F} = \varepsilon_{\rm F}^0 + 25$ meV) TaAs. Panels (b) and (c) show quantities evaluated at 300 K, with results for the undoped system ($\varepsilon_{\rm F}=\varepsilon_{\rm F}^0$) included for comparison. In panel (c), the energy-averaged scattering rates are shown as solid lines.
• Figure 5: Frequency-resolved scattering rate $\partial \tau^{-1}(\varepsilon)/\partial \omega$ (solid curves, left axis) and cumulative integral $\int_0^{\omega} \rm{d}\omega'\partial \tau^{-1}(\varepsilon)/\partial \omega'$ (dashed curves, right axis) evaluated at the Fermi level for undoped ($\varepsilon_{\rm F} = \varepsilon_{\rm F}^0$), hole-doped ($\varepsilon_{\rm F} = \varepsilon_{\rm F}^0 - 25$ meV), and electron-doped ($\varepsilon_{\rm F} = \varepsilon_{\rm F}^0 + 25$ meV) systems at 300 K.