Broken Symmetries and Kohn’s Theorem in Graphene Cyclotron Resonance

Abstract

The cyclotron resonance of monolayer graphene, encapsulated in hexagonal boron nitride and with a graphite backgate, is explored via infrared transmission magnetospectroscopy as a function of the filling factor at fixed magnetic fields. The impact of many-particle interactions in the regime of broken spin and valley symmetries is observed spectroscopically. As the occupancy of the zeroth Landau level is increased from half-filling, a nonmonotonic progression of multiple cyclotron resonance peaks is seen for several interband transitions, revealing the evolution of underlying many-particle-enhanced gaps. Analysis of the peak energies shows significant exchange enhancements of spin gaps both at and below the Fermi energy, a strong filling-factor dependence of the substrate-induced Dirac mass, and also the smallest particle-hole asymmetry reported to date in graphene cyclotron resonance.

Cyclotron Resonance Study of Monolayer Graphene under Double Moiré Potentials

“…This plot reproduces the observed eyeglass-like pattern for −2 < ν < 2 and also explains the weaker intensities of the signals at higher magnetic fields (e2 and h2) with respect to those of the signals at lower magnetic fields (e1 and h1). Our CR experiment suggests that Δ g spin ∼ 12 when E F lies in the middle of the spin gaps (|ν| = 1), which is consistent with the observations from a recent STM study and CR spectrocopy. , We note that although we assumed B CR versus ν is constant for |ν| > 2 (Figure f), the experiment reveals arc-like shapes for the CR signals when |ν| > 2 (Figure e). This observation suggests that v F renormalization occurs, depending on ν, because of the different degrees of many-particle interactions (see the Supporting Information).…”

“…Figure 4f 1), which is consistent with the observations from a recent STM study 39 and CR spectrocopy. 41,42 We note that although we assumed B CR versus ν is constant for |ν| > 2 (Figure 4f), the experiment reveals arc-like shapes for the CR signals when |ν| > 2 (Figure 4e). This observation suggests that v F renormalization occurs, depending on ν, because of the different degrees of many-particle interactions (see the Supporting Information).…”

“…Note : During the preparation of this manuscript, we became aware of an arXiv article that reports an infrared spectroscopic study of h-BN-encapsulated graphene . The paper discusses the breaking of spin and valley symmetries in nonaligned graphene.…”

Landau level spectroscopy of the PbSnSe topological crystalline insulator

“…The magneto-optical response of systems with such a LL spectrum has been widely studied, both theoretically and experimentally, on graphene and other systems [46,47,[49][50][51][52][53][54][55]. The response is dominated by a series of interband and intraband inter-LL excitations that follow the standard electric-dipole selection rules in isotropic systems: n → n ± 1.…”

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

“…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. [36]. They observed significant variations of resonance energies over a finite range of filling factor ν under a fixed magnetic field B; the point lies in extracting genuine Coulombic effects as a function of ν while controlling the running of the velocity factor with B.…”