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Bilayer graphene
About: Bilayer graphene is a research topic. Over the lifetime, 7007 publications have been published within this topic receiving 428616 citations.
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TL;DR: In this article , the intrinsic and modulated optical properties of the AB-stacking bilayer armchair graphene ribbons in the absence and presence of external electric fields have been investigated.
Abstract: In this work, we investigate the intrinsic as well as modulated optical properties of the AB-stacking bilayer armchair graphene ribbons in the absence and presence of external electric fields. Single-layer ribbons are also considered for comparison. By using a tight-binding model in combination with the gradient approximation, we examine the energy bands, the density of states and the absorption spectra of the studied structures. Our results demonstrate that when external fields are not present, the low-frequency optical absorption spectra display numerous peaks and they vanish at the zero point. In addition, the number, the position, and the intensity of the absorption peaks are strongly associated with the ribbon width. With the wider ribbon width, more absorption peaks are present and a lower threshold absorption frequency is observed. Interestingly, in the presence of electric fields, bilayer armchair ribbons exhibit a lower threshold absorption frequency, more absorption peaks, and weaker spectral intensity. When increasing the strength of the electric field, the prominent peaks of the edge-dependent selection rules are lowered, and the sub-peaks satisfying the extra selection rules come to exist. The obtained results certainly provide a more comprehensive understanding of the correlation between the energy band transition and the optical absorption, in both single-layer and bilayer graphene armchair ribbons, and could provide new insights into developments of optoelectronic device applications based on graphene bilayer ribbons.
TL;DR: In this paper, the zero-temperature conductivity of bilayer graphene (BLG) impacted by Coulomb impurity scattering using four different screening models: unscreened, Thomas-Fermi (TF), over-screened and random phase approximation (RPA).
Abstract: We calculate the zero-temperature conductivity of bilayer graphene (BLG) impacted by Coulomb impurity scattering using four different screening models: unscreened, Thomas–Fermi (TF), overscreened and random phase approximation (RPA). We also calculate the conductivity and thermal conductance of BLG using TF, zero- and finite-temperature RPA screening functions. We find large differences between the results of the models and show that TF and finite-temperature RPA give similar results for diffusion thermopower Sd. Using the finite-temperature RPA, we calculate temperature and density dependence of Sd in BLG on SiO2, HfO2 substrates and suspended BLG for different values of interlayer distance c and distance between the first layer and the substrate d.
TL;DR: In this article, a micromechanical cleavage method is used to produce grapheme, which is acquired by peeling graphite foil off from transparent sticky tape repeatedly.
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TL;DR: In this article, a family of twisted bilayer graphene (CTBG) multilayers with a single twist on top of the stacked layers was considered, and it was shown that the Berry curvature distribution can be continuously tuned while maintaining perfect quantum geometry.
Abstract: We consider a family of twisted graphene multilayers consisting of $n$-untwisted {chirally stacked layers, e.g. AB, ABC, etc,} with a single twist on top of $m$-untwisted {chirally stacked} layers. Upon neglecting both trigonal warping terms for the untwisted layers and the same sublattice hopping between all layers, the resulting models generalize several remarkable features of the chiral model of twisted bilayer graphene (CTBG). {In particular, they exhibit a set of magic angles which are identical to those of CTBG at which a pair of bands (i) are perfectly flat, (ii) have Chern numbers in the sublattice basis given by $\pm (n,-m)$ or $\pm (n+m-1,-1)$ depending on the stacking chirality, and (iii) satisfy the trace condition, saturating an inequality between the quantum metric and the Berry curvature, and thus realizing ideal quantum geometry}. We provide explicit analytic expressions for the flat band wavefunctions at the magic angle in terms of the CTBG wavefunctions. We also show that the Berry curvature distribution in these models can be continuously tuned while maintaining perfect quantum geometry. Similar to the study of fractional Chern insulators in ideal $C = 1$ bands, these models pave the way for investigating exotic topological phases in higher Chern bands for which no Landau level analog is available.
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TL;DR: In this article, an unbiased renormalization group approach has been used to show that TMDs are unique platforms to realize topological superconductivity with winding number $|\mathcal{N}|=4$.
Abstract: Experimental demonstrations of tunable correlation effects in magic-angle twisted bilayer graphene have put two-dimensional moire quantum materials at the forefront of condensed-matter research. Other twisted few-layer graphitic structures, boron-nitride, and homo- or hetero-stacks of transition metal dichalcogenides (TMDs) have further enriched the opportunities for analysis and utilization of correlations in these systems. Recently, within the latter material class, strong spin-orbit coupling or excitonic physics were experimentally explored. The observation of a Mott insulating state and other fascinating collective phenomena such as generalized Wigner crystals, stripe phases and quantum anomalous Hall insulators confirmed the relevance of many-body interactions, and demonstrated the importance of their extended range. Since the interaction, its range, and the filling can be tuned experimentally by twist angle, substrate engineering and gating, we here explore Fermi surface instabilities and resulting phases of matter of hetero-bilayer TMDs. Using an unbiased renormalization group approach, we establish in particular that hetero-bilayer TMDs are unique platforms to realize topological superconductivity with winding number $|\mathcal{N}|=4$. We show that this state reflects in pronounced experimental signatures, such as distinct quantum Hall features.