Magneto-optical conductivity of graphene on polar substrates

TL;DR

This paper theoretically investigates how polar substrates influence the magneto-optical conductivity of doped graphene, highlighting the significant role of surface polar phonons and temperature-dependent effects on optical absorption features.

Contribution

It introduces a detailed theoretical model accounting for surface polar phonons and impurity scattering, revealing their impact on graphene's magneto-optical properties on polar substrates.

Findings

Polaronic shifts are larger on substrates with strong electron-SPP coupling.

Temperature increases lead to greater effects of polar substrates on conductivity.

Impurity scattering influences absorption peak lineshapes, especially at low temperatures.

Abstract

We theoretically study the effect of polar substrates on the magneto-optical conductivity of doped monolayer graphene, where we particularly focus on the role played by surface polar phonons (SPPs). Our calculations suggest that polaronic shifts of the intra- and interband absorption peaks can be significantly larger for substrates with strong electron-SPP coupling than those in graphene on non-polar substrates, where only intrinsic graphene optical phonons with much higher energies contribute. Electron-phonon scattering and phonon-assisted transitions are, moreover, found to result in a loss of spectral weight at the absorption peaks. The strength of these processes is strongly temperature-dependent and with increasing temperatures the magneto-optical conductivity becomes increasingly affected by polar substrates, most noticeably in polar substrates with small SPP energies such as HfO$_2$. The inclusion of a Landau level-dependent scattering rate to account for Coulomb impurity scattering does not alter this qualitative picture, but can play an important role in determining the lineshape of the absorption peaks, especially at low temperatures, where impurity scattering dominates.