Many-body filling factor dependent renormalization of Fermi velocity in graphene in strong magnetic field

Abstract

We present the theory of many-body corrections to cyclotron transition energies in graphene in strong magnetic field due to Coulomb interaction, considered in terms of the renormalized Fermi velocity. A particular emphasis is made on the recent experiments where detailed dependencies of this velocity on the Landau level filling factor for individual transitions were measured. Taking into account the many-body exchange, excitonic corrections and interaction screening in the static random-phase approximation, we successfully explained the main features of the experimental data, in particular that the Fermi velocities have plateaus when the 0th Landau level is partially filled and rapidly decrease at higher carrier densities due to enhancement of the screening. We also explained the features of the nonmonotonous filling-factor dependence of the Fermi velocity observed in the earlier cyclotron resonance experiment with disordered graphene by taking into account the disorderinduced Landau level broadening.

Broken Symmetries and Kohn’s Theorem in Graphene Cyclotron Resonance

“…These schematics are drawn for ν ¼ 0; þ1, and þ2, with each of the four spin and valley levels shown explicitly, albeit with greatly exaggerated level shifts and gap sizes. In graphene, the inapplicability of Kohn's theorem implies the CR transition energies will reflect the single-particle LL separations plus many-particle shifts of the levels, along with excitonic and exchange corrections due to the excited electron and remnant hole [18][19][20]35,36]. Of course, the measured energies do not indicate which portion is due to level shifts vs exciton corrections.…”

Many-body effects, orbital mixing, and cyclotron resonance in bilayer graphene

“…Presumably, when ν changes over a wide range as in Fig. 6, screening of the Coulomb potential v p will become important, as noted [33,34] for monolayer graphene. Via screening v p will get weaker with increasing |ν|, making the spectra decrease faster for larger |ν|.…”

“…In experiment CR has been explored for monolayer [22][23][24] and bilayer [25,26] graphene. Many-body effects on CR [27][28][29][30][31][32][33][34] were first detected rather indirectly by a comparison of some leading intraband and interband resonances [22]. Recently, Russell et al [35] have reported a direct signal of manybody effects on CR in high-mobility hBN-encapsulated monolayer graphene; see also ref.…”

Broken symmetries and Kohn's theorem in graphene cyclotron resonance

“…A key consequence of electron interactions in graphene is to renormalize the band velocity v → ṽ [6,[23][24][25]; in a magnetic field ṽ decreases weakly with increasing B, or at fixed field it is roughly constant when the lowest LL is partially filled and declines sharply as higher LLs become occupied [13]. Many-particle contributions have been seen in CR and magneto-Raman experiments [6,[11][12][13][14][15], and generally good agreement with theory has been found [8,9,17,18,26].…”