Infrared magneto-spectroscopy of two-dimensional and three-dimensional massless fermions: A comparison (original) (raw)
Related papers
Nanoscale Research Letters, 2012
Massless Dirac electrons in graphene fill Landau levels with energies scaled as square roots of their numbers. Coulomb interaction between electrons leads to mixing of different Landau levels. The relative strength of this interaction depends only on dielectric susceptibility of surrounding medium and can be large in suspended graphene. We consider influence of Landau level mixing on the properties of magnetoexcitons and magnetoplasmons-elementary electron-hole excitations in graphene in quantizing magnetic field. We show that, at small enough background dielectric screening, the mixing leads to very essential change of magnetoexciton and magnetoplasmon dispersion laws in comparison with the lowest Landau level approximation.
Physical Review B, 2009
We present a calculation of the modulation in the Local Density Of electronic States (LDOS) caused by an impurity in graphene in the presence of external magnetic field. We focus on the spatial Fourier Transform (FT) of this modulation around the impurity. The FT due to the low energy quasiparticles are found to be nonzero over the reciprocal lattice corresponding to graphene. At these lattice spots the FT exhibits well-defined features at wavevectors that are multiples of the inverse cyclotron orbit diameter (see Figure 2) and is cut off at the wavevector corresponding to the energy of observation. Scanning Tunneling Spectroscopy (STS) on graphene and the energy-resolved FT fingerprint obtained therefrom may be used to observe the quasiparticle interference of Dirac particles in graphene in the presence of magnetic field.
Magneto-Spectroscopy of Epitaxial Graphene
International Journal of Modern Physics B
We present a far infrared investigation of the optical transitions in epitaxial graphene subjected to a perpendicular magnetic field. Cyclotron-resonance-like transitions between adjacent electron Landau levels are observed, as well as interband transitions. The results are discussed in terms of existing theoretical models of Dirac fermions in graphene, and the relevant optical selection rules.
Rabi Oscillations in Landau-Quantized Graphene
Physical Review Letters, 2009
The canonical model of quantum optics, the Jaynes-Cummings Hamiltonian describes a two level atom in a cavity interacting with electromagnetic field. Graphene, a condensed matter system, possesses low energy excitations obeying to the Dirac equation, and mimics the physics of quantum electrodynamics. These two seemingly unrelated fields turn out to be closely related to each other. We demonstrate that Rabi oscillations, corresponding to the excitations of the atom in the former case are observable in the optical response of the latter in quantizing magnetic field, providing us with a transparent picture about the structure of optical transitions in graphene. While the longitudinal conductivity reveals chaotic Rabi oscillations, the Hall component measures coherent ones. This opens up the exciting possibility of investigating a microscopic model of a few quantum objects in a macroscopic experiment of a bulk material with tunable parameters.
Anomalous Absorption Line in the Magneto-Optical Response of Graphene
Physical Review Letters, 2007
The intensity as well as position in energy of the absorption lines in the infrared conductivity of graphene, both exhibit features that are directly related to the Dirac nature of its quasiparticles. We show that the evolution of the pattern of absorption lines as the chemical potential is varied encodes the information about the presence of the anomalous lowest Landau level. The first absorption line related to this level always appears with full intensity or is entirely missing, while all other lines disappear in two steps. We demonstrate that if a gap develops, the main absorption line splits into two provided that the chemical potential is greater than or equal to the gap.
Tunable interactions and phase transitions in Dirac materials in a magnetic field
Physical Review B, 2011
A partially filled Landau level (LL) hosts a variety of correlated states of matter with unique properties. The ability to control these phases requires tuning the effective electron interactions within a LL, which has been difficult to achieve in GaAs-based structures. Here we consider a class of Dirac materials in which the chiral band structure, along with the mass term, give rise to a wide tunability of the effective interactions by the magnetic field. This tunability is such that different phases can occur in a single LL, and phase transitions between them can be driven in situ. The incompressible, Abelian and non-Abelian, liquids are stabilized in new interaction regimes. Our study points to a realistic method of controlling the correlated phases and studying the phase transitions between them in materials such as graphene, bilayer graphene, and topological insulators.
Physical Review Letters, 2008
We have investigated the absorption spectrum of multilayer graphene in high magnetic fields. The low energy part of the spectrum of electrons in graphene is well described by the relativistic Dirac equation with a linear dispersion relation. However, at higher energies (>500 meV) a deviation from the ideal behavior of Dirac particles is observed. At an energy of 1.25 eV, the deviation from linearity is 40 meV. This result is in good agreement with the theoretical model, which includes trigonal warping of the Fermi surface and higher-order band corrections. Polarization-resolved measurements show no observable electron-hole asymmetry.
Magneto-optical properties of a semi-Dirac nanoribbon in the terahertz frequency regime
arXiv (Cornell University), 2021
We study magneto-optical (MO) properties of a semi-Dirac nanoribbon in presence of a perpendicular magnetic field using Kernel Polynomial Method (KPM) based on the Keldysh formalism in the experimental (terahertz frequency) regime. For comparison, we have also included results for the Dirac systems as well, so that the interplay of the band structure deformation and MO conductivities can be studied. We have found that the MO conductivity shows features in the semi-Dirac system that are quite distinct from the Dirac case near the ultraviolet and the visible regimes. The real parts of the longitudinal conductivities, namely Re(σxx) and Re(σyy) (which are different in the semi-Dirac case, as opposed to a Dirac one) present a series of resonance peaks as a function of the incident photon energy. We have also found that the absorption peaks corresponding to the y-direction are larger (roughly one order of magnitude) than those corresponding to the x-direction for the semi-Dirac case. In the case of the Hall conductivity, that is, Re(σxy), there are extra peaks in the spectra compared to the Dirac case which originate from the distinct optical transitions of the carriers from one Landau level to another. We have also explored how the carrier concentration influences the MO conductivities. In the semi-Dirac case, there is the emergence of additional peaks yet again in the absorption spectrum underscoring the presence of an asymmetric dispersion compared to the Dirac case. Further, we have explored the interplay between the polarization of the incident beam and the features of the absorption spectra which can be probed in experiments. Finally, we evaluate the MO activity of the medium by computing the Faraday rotation angle, θF .
Phys Rev B, 2005
The quantum magnetic oscillations of electrical (Shubnikov-de Haas effect) and thermal conductivities are studied for graphene which represents a distinctive example of planar systems with a linear, Dirac-like spectrum of quasiparticle excitations. We show that if utmost care is taken to separate electron and phonon contributions in the thermal conductivity, the oscillations of electron thermal conductivity κ(B) and Lorenz number, L(B) would be observable in the low-field (less than a few teslas) regime.