اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدMeasurement of the electronic compressibility of bilayer graphene
297
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present measurements of the electronic compressibility, $K$, of bilayer graphene in both zero and finite magnetic fields up to 14 T, and as a function of both the carrier density and electric field perpendicular to the graphene sheet. The low energy hyperbolic band structure of bilayer graphene is clearly revealed in the data, as well as a sizable asymmetry between the conduction and valence bands. A sharp increase in $K^{-1}$ near zero density is observed for increasing electric field strength, signaling the controlled opening of a gap between these bands. At high magnetic fields, broad Landau level (LL) oscillations are observed, directly revealing the doubled degeneracy of the lowest LL and allowing for a determination of the disorder broadening of the levels.
قيم البحث
اقرأ أيضاً
We study the electronic properties of twisted bilayers graphene in the tight-binding approximation. The interlayer hopping amplitude is modeled by a function, which depends not only on the distance between two carbon atoms, but also on the positions
of neighboring atoms as well. Using the Lanczos algorithm for the numerical evaluation of eigenvalues of large sparse matrices, we calculate the bilayer single-electron spectrum for commensurate twist angles in the range $1^{circ}lesssimthetalesssim30^{circ}$. We show that at certain angles $theta$ greater than $theta_{c}approx1.89^{circ}$ the electronic spectrum acquires a finite gap, whose value could be as large as $80$ meV. However, in an infinitely large and perfectly clean sample the gap as a function of $theta$ behaves non-monotonously, demonstrating exponentially-large jumps for very small variations of $theta$. This sensitivity to the angle makes it impossible to predict the gap value for a given sample, since in experiment $theta$ is always known with certain error. To establish the connection with experiments, we demonstrate that for a system of finite size $tilde L$ the gap becomes a smooth function of the twist angle. If the sample is infinite, but disorder is present, we expect that the electron mean-free path plays the same role as $tilde L$. In the regime of small angles $theta<theta_c$, the system is a metal with a well-defined Fermi surface which is reduced to Fermi points for some values of $theta$. The density of states in the metallic phase varies smoothly with $theta$.
We study, within the tight-binding approximation, the electronic properties of a graphene bilayer in the presence of an external electric field applied perpendicular to the system -- emph{biased bilayer}. The effect of the perpendicular electric fiel
d is included through a parallel plate capacitor model, with screening correction at the Hartree level. The full tight-binding description is compared with its 4-band and 2-band continuum approximations, and the 4-band model is shown to be always a suitable approximation for the conditions realized in experiments. The model is applied to real biased bilayer devices, either made out of SiC or exfoliated graphene, and good agreement with experimental results is found, indicating that the model is capturing the key ingredients, and that a finite gap is effectively being controlled externally. Analysis of experimental results regarding the electrical noise and cyclotron resonance further suggests that the model can be seen as a good starting point to understand the electronic properties of graphene bilayer. Also, we study the effect of electron-hole asymmetry terms, as the second-nearest-neighbor hopping energies $t$ (in-plane) and $gamma_{4}$ (inter-layer), and the on-site energy $Delta$.
The generalized tight-binding model is developed to investigate the magneto-electronic properties in twisted bilayer graphene system. All the interlayer and intralayer atomic interactions are included in the Moire superlattice. The twisted bilayer gr
aphene system is a zero-gap semiconductor with double-degenerate Dirac-cone structures, and saddle-point energy dispersions appearing at low energies for cases of small twisting angles. There exist rich and unique magnetic quantization phenomena, in which many Landau-level subgroups are induced due to specific Moire zone folding through modulating the various stacking angles. The Landau-level spectrum shows hybridized characteristics associated with the those in monolayer, and AA $&$ AB stackings. The complex relations among the different sublattices on the same and different graphene layers are explored in detail.
In this paper, we study the quantum properties of a bilayer graphene with (asymmetry) line defects. The localized states are found around the line defects. Thus, the line defects on one certain layer of the bilayer graphene can lead to an electric tr
ansport channel. By adding a bias potential along the direction of the line defects, we calculate the electric conductivity of bilayer graphene with line defects using Landauer-B{u}ttiker theory, and show that the channel affects the electric conductivity remarkably by comparing the results with those in a perfect bilayer graphene. This one-dimensional line electric channel has the potential to be applied in the nanotechnology engineering.
The electronic and optical response of Bernal stacked bilayer graphene with geometry modulation and gate voltage are studied. The broken symmetry in sublattices, one dimensional periodicity perpendicular to the domain wall and out-of-plane axis intro
duces substantial changes of wavefunctions, such as gapless topological protected states, standing waves with bonding and anti-bonding characteristics, rich structures in density of states and optical spectra. The wavefunctions present well-behaved standing waves in pure system and complicated node structures in geometry-modulated system. The optical absorption spectra show forbidden optical excitation channels, prominent asymmetric absorption peaks, and dramatic variations in absorption structures. These results provide that the geometry-modulated structure with tunable gate voltage could be used for electronic and optical manipulation in future graphene-based devices.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
