Anomalous plasmon mode in strained Weyl semimetals

An exotic anomalous plasmon (AP) mode is found in strained Weyl semimetals utilizing the topological Landau Fermi liquid and chiral kinetic theories, in which quasiparticle interactions are modeled by long-range Coulomb and residual short-range interactions. The gapped collective mode is derived from the dynamical charge pumping between the bulk and the surface and behaves like $k_{\mathrm{F}}^{-1}$. The charge oscillations are accurately determined by the coupling between the induced electric field and the background pseudofields. This novel mode unidirectionally disperses along the pseudomagnetic field and manifests itself in an unusual thermal conductivity in apparent violation of the Wiedemann-Franz law. The excitation can be achieved experimentally by mechanical vibrations of the crystal lattice in the THz regime.

Figure 1

(a) Colored disks represent the coherent breathing-like fluctuation of the bulk Fermi surfaces for a single pair of Weyl nodes owing to the anomaly-induced charge transfer between the bulk and the surface. The dashed circles denote the equilibrium position of the Fermi surfaces ${\mu }_{\chi }^{\left(eq\right)}=\mu +\chi \left|\delta {\mu }_{\chi }^{\left(1\right)}\right|$. (b) The blue and green lines denote the charge density creation and annihilation when $\psi$ sweep along $[0,2\pi ]$ and $\delta n_{\chi }^{\left(1\right)}$ represents the chirality imbalance between two nodes due to the term $\propto {\mathcal{E}}^{\mathit{el}}·{\mathcal{B}}^{\mathit{el}}$ in the chiral anomaly equation. We define $\psi =\mathit{q}·\mathit{r}-\omega t$ as a quantum phase of the collective motion of charges.

Figure 2

(a) The renormalized specific heat ${\tilde{\mathcal{C}}}_v=(4{\pi }^2{(1+a_2)}^{3/2}/k_B{\mathrm{\Lambda }}^3){\mathcal{C}}_v$ as a function of temperature. The temperature is plotted in the units of Debye temperature for ${\mathrm{\Theta }}_{AP}=\alpha \mathrm{\Lambda }/k_B$, where $\alpha ={\mathcal{B}}^{el}/2k_F^2$. The active presence of repulsive short-range interaction ${\mathcal{F}}_0$ generates the specific heat to increase, especially in the higher temperature regions. We set $a_1={\mathrm{\Lambda }}^2$ and $a_2=0,0.1$ for the blue and the green lines, respectively. (b) The renormalized thermal conductivity ${\tilde{\kappa }}_{zz}^{th}=[4{\pi }^2/k_B{\tau }_p{\mathrm{\Lambda }}^3{(1+a_2)}^{1/2}]{\kappa }_{zz}^{th}$ as a function of pseudomagnetic field ${\mathcal{B}}^{el}$ for temperatures $T/{\mathrm{\Theta }}_{AP}=0.5,1,5$, with $a_1={\mathrm{\Lambda }}^2$ and $a_2=1$.