19 research outputs found
Sublattice asymmetry and spin-orbit interaction induced out-of-plane spin polarization of photoelectrons
No full textWe study theoretically the effect of spin-orbit coupling and sublattice asymmetry in graphene on the spin polarization of photoelectrons. We show that sublattice asymmetry in graphene not only opens a gap in the band structure, but in the case of finite spin-orbit interaction it also gives rise to an out-of-plane spin polarization of electrons close to the Dirac point of the Brillouin zone. This can be detected by measuring the spin polarization of photoelectrons, and therefore spin-resolved photoemission spectroscopy can reveal the presence of a band gap even if it is too small to be observed directly by angle-resolved photoemission spectroscopy because of the finite resolution of measurements or because the sample is p-doped. We present analytical and numerical calculations on the energy and linewidth dependence of photoelectron intensity distribution and spin polarization
Trigonal warping and anisotropic band splitting in monolayer graphene due to Rashba spin-orbit coupling
No full textWe study the electronic band structure of monolayer graphene when Rashba spin-orbit coupling is present. We show that if the Rashba spin-orbit coupling is stronger than the intrinsic spin-orbit coupling, the low-energy bands undergo trigonal-warping deformation and that for energies smaller than the Lifshitz energy, the Fermi circle breaks up into separate parts. The effect is very similar to what happens in bilayer graphene at low energies. We discuss the possible experimental implications, such as threefold increase in the minimal conductivity for low electron densities, anisotropic, wave-number-dependent spin splitting of the bands, and the spin-polarization structure
Exploring the graphene edges with coherent electron focusing
No full textWe study theoretically the coherent electron focusing in graphene nanoribbons. Using semiclassical and numerical tight-binding calculations we show that armchair edges give rise to equidistant peaks in the focusing spectrum. In the case of zigzag edges at low magnetic fields one can also observe focusing peaks but with increasing magnetic field a more complex interference structure emerges in the spectrum. This difference in the spectra can be observed even if the zigzag edge undergoes structural reconstruction. Therefore transverse electron focusing can help in the identification and characterization of the edge structure of graphene samples
Bound states in inhomogeneous magnetic field in graphene : Semiclassical approach
No full textWe derive semiclassical quantization equations for graphene
monolayer
and bilayer systems where the excitations are confined by the
applied
inhomogeneous magnetic field. The importance of a semiclassical
phase,
a consequence of the spinor nature of the excitations, is
pointed out.
The semiclassical eigenenergies show good agreement with the
results of
quantum-mechanical calculations based on the Dirac equation of
graphene
and with numerical tight-binding calculations
Electronic standing waves on the surface of the topological insulator Bi2Te3
No full textA line defect on a metallic surface induces standing waves in the electronic local density of states (LDOS). Asymptotically far from the defect, the wave number of the LDOS oscillations at the Fermi energy is usually equal to the distance between nesting segments of the Fermi contour, and the envelope of the LDOS oscillations shows a power-law decay as moving away from the line defect. Here, we theoretically analyze the LDOS oscillations close to a line defect on the surface of the topological insulator Bi 2Te 3, and identify an important preasymptotic contribution with wave-number and decay characteristics markedly different from the asymptotic contributions. The calculated energy dependence of the wave number of the preasymptotic LDOS oscillations is in quantitative agreement with the result of a recent scanning tunneling microscopy experiment. © 2012 American Physical Society
Landau levels and Shubnikov-de Haas oscillations in monolayer transition metal dichalcogenide semiconductors
No full textWe study the Landau level (LL) spectrum using a multi-band theory in monolayer transition metal dichalcogenide semiconductors. We find that in a wide magnetic field range the LL can be characterized by a harmonic oscillator spectrum and a linear-in-magnetic field term which describes the valley degeneracy breaking. The effect of the non-parabolicity of the band-dispersion on the LL spectrum is also discussed. Motivated by recent magnetotransport experiments, we use the self-consistent Born approximation and the Kubo formalism to calculate the Shubnikov–de Haas oscillations of the longitudinal conductivity. We investigate how the doping level, the spin-splitting of the bands and the broken valley degeneracy of the LLs affect the magnetoconductance oscillations. We consider monolayer MoS2 and WSe2 as concrete examples and compare the results of numerical calculations and an analytical formula which is valid in the semiclassical regime. Finally, we briefly analyze the recent experimental results (Cui et al 2015 Nat. Nanotechnol. 10 534) using the theoretical approach we have developed.publishe
This content has been downloaded from IOPscience. Please scroll down to see the full text. Landau levels and Shubnikov-de Haas oscillations in monolayer transition metal dichalcogenide semiconductors Landau levels and Shubnikov-de Haas oscillations in mon
No full textAbstract We study the Landau level (LL) spectrum using a multi-band k p · theory in monolayer transition metal dichalcogenide semiconductors. We find that in a wide magnetic field range the LL can be characterized by a harmonic oscillator spectrum and a linear-in-magnetic field term which describes the valley degeneracy breaking. The effect of the non-parabolicity of the band-dispersion on the LL spectrum is also discussed. Motivated by recent magnetotransport experiments, we use the selfconsistent Born approximation and the Kubo formalism to calculate the Shubnikov-de Haas oscillations of the longitudinal conductivity. We investigate how the doping level, the spin-splitting of the bands and the broken valley degeneracy of the LLs affect the magnetoconductance oscillations. We consider monolayer MoS 2 and WSe 2 as concrete examples and compare the results of numerical calculations and an analytical formula which is valid in the semiclassical regime. Finally, we briefly analyze the recent experimental results (Cui et al 2015 Nat. Nanotechnol. 10 534) using the theoretical approach we have developed
Theory of snake states in graphene
No full textWe study the dynamics of the electrons in a nonuniform magnetic field applied perpendicular to a graphene sheet in the low-energy limit when the excitation states can be described by a Dirac-type Hamiltonian. Compared to two-dimensional electron gas systems, we show that snake states in graphene exhibit peculiar properties related to the underlying dynamics of the Dirac fermions. The current carried by snake states is locally uncompensated, leading to a current inhomogeneity in the ground state
Effect of the band structure topology on the minimal conductivity for bilayer graphene with symmetry breaking
No full textUsing the Kubo formula we develop a general and simple
expression for the minimal conductivity in systems described by
a 2×2 Hamiltonian. As an application we derive an analytical
expression for the minimal conductivity tensor of bilayer
graphene as a function of a complex parameter w related to
recently proposed symmetry breaking mechanisms resulting from
electron-electron interaction or strain applied to the sample.
The number of Dirac points changes with varying parameter w, and
this directly affects the minimal conductivity. Our analytic
expression is confirmed using an independent calculation based
on the Landauer approach, and we find remarkably good agreement
between the two methods. We demonstrate that the minimal
conductivity is very sensitive to the change of the parameter w
and the orientation of the electrodes with respect to the
sample. Our results show that the minimal conductivity is
closely related to the topology of the low-energy band
structure
