Predicting a Gapless Spin-1 Neutral Collective Mode branch for Graphite
Abstract
Using the standard tight binding model of 2d graphite with short range electron repulsion, we find a gapless spin-1, neutral collective mode branch below the particle-hole continuum with energy vanishing linearly with momenta at the and K points in the BZ. This spin-1 mode has a wide energy dispersion, 0 to 2 eV and is not Landau damped. The `Dirac cone spectrum' of electrons at the chemical potential of graphite generates our collective mode; so we call this `spin-1 zero sound' of the `Dirac sea'. Epithermal neutron scattering experiments, where graphite single crystals are often used as analyzers (an opportunity for `self-analysis'!), and spin polarized electron energy loss spectroscopy (SPEELS) can be used to confirm and study our collective mode.
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