Anatomy of plasmons in generic Luttinger semimetals

Kavli Affiliate: Jing Wang

| Authors: Jing Wang, Ipsita Mandal

| Summary:

We investigate the parameter regimes favourable for the emergence of plasmons
in isotropic, anisotropic, and band-mass asymmetric Luttinger semimetals
(LSMs). An LSM harbours a quadratic band-crossing point (QBCP) in its
bandstructure, where the upper and lower branches of dispersion are doubly
degenrate. While a nonzero temperature ($T$) can excite particle-hole pairs
about the Fermi level due to thermal effects (even at zero doping), a finite
doping ($mu$) sets the Fermi level away from the QBCP at any $T$, leading to a
finite Fermi surface (rather than a Fermi point). Both these conditions
naturally give rise to a finite density of states. A nonzero value of $T$ or
$mu$ is thus a necessary condition for a plasmon to exist, as otherwise the
zero density of states at the QBCP can never lead to the appearance of this
collective mode. In addition to $T$ and $mu$, we consider the effects of all
possible parameters like cubic anisotropy, band-mass asymmetry, and a
material-dependent parameter $X$, to numerically compute the quasiparticle
damping rate $tau$ resulting from screened Coulomb interactions. A
well-defined sharp peak in the profile of the inelastic scattering rate
$tau^{-1}$ signals the appearance of a plasmon. From our results, we conclude
that $X$ turns out to be a crucial tuning parameter, as higher values of $X$
assist in the emergence of plasmons. On the other hand, the features are
broadly insensitive to cubic anisotropy and band-mass asymmetry.

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