Speaker
Description
Background: In 2013, we reported strong electron-phonon coupling (EPC) in the σ-bands of graphene [1]. This observation was highly controversial at the time, and attempts were made to dismiss it as a consequence of photoemission matrix elements instead [2]. We endeavoured to clear up this controversy by i) theoretical support and ii) manipulating the photoemission matrix elements by measuring in the neighbouring BZs and on bilayer samples, confirming mass enhancements of 𝜆 ≈ 0.7 [3].
Since then, we have predicted that hBN should host similarly strong EPC in its σ-bands [4]. This is unsurprising since the electronic structure, phonon structure, geometry, are all similar to graphene. On the other hand, experimental confirmation adds further credence to our understanding of EPC in graphene’s σ-bands. Contrastingly, we predict strong EPC in the π-band of hBN. hBN’s π-band has a parabolic maxima, making the EPC arguments (especially the scattering k-space) very different to graphene, and leading to much stronger EPC.
Most recently, we have confirmed the presence of strong EPC in both the π- and σ-bands of hBN. Furthermore, we show that the EPC strength in the π-band depends strongly on doping and/or substrate interaction, thus making it possible to further enhance the EPC (specifically with K and Cl intercalants). Several questions remain unanswered, and are the focus of ongoing work: including further ARPES studies, DFT and helium scattering studies.
In this talk, I will give a short overview of the unusual EPC in graphene’s σ-bands, as well as presenting our most recent studies of monolayer hBN with dopants and intercalants. I will briefly present the helium scatting work and conclude with our latest understanding and some as yet unanswered questions.
References:
[1] F Mazzola, et al., “Kinks in the Band of Graphene Induced by Electron-Phonon Coupling" Phys. Rev. Lett 111:216806 (2013)
[2] SW Jung et al., “Sublattice Interference as the Origin of 𝜎 Band Kinks in Graphene”
Phys. Rev. Lett. 116:186802 (2016)
[3] F. Mazzola et al., “Strong electron-phonon coupling in the 𝜎 band of graphene”
Phys. Rev. B 95:075430 (2017)
[4] E. Thingstad et al., "Phonon-mediated superconductivity in doped monolayer materials”
Phys. Rev. B 101, p. 214513 (2020)