8 research outputs found
One-dimensional moir\'e superlattices and flat bands in collapsed chiral carbon nanotubes
We demonstrate that one-dimensional moir\'e patterns, analogous to those
found in twisted bilayer graphene, can arise in collapsed chiral carbon
nanotubes. Resorting to a combination of approaches, namely, molecular dynamics
to obtain the relaxed geometries and tight-binding calculations validated
against ab initio modeling, we find that magic angle physics occur in collapsed
carbon nanotubes. Velocity reduction, flat bands and localization in AA regions
with diminishing moir\'e angle are revealed, showing a magic angle close to
1. From the spatial extension of the AA regions and the width of the
flat bands, we estimate that many-body interactions in these systems are
stronger than in twisted bilayer graphene. Chiral collapsed carbon nanotubes
stand out as promising candidates to explore many-body effects and
superconductivity in low dimensions, emerging as the one-dimensional analogues
of twisted bilayer graphene
Universality of moir\'e physics in collapsed chiral carbon nanotubes
We report the existence of moir\'e patterns and magic angle physics in all
families of chiral collapsed carbon nanotubes. A detailed study of the
electronic structure of all types of chiral nanotubes, previously collapsed via
molecular dynamics, has been performed. We find that each family possesses a
unique geometry and moir\'e disposition, as well as a characteristic number of
flat bands. Remarkably, all kinds of nanotubes behave the same with respect to
magic angle tuning, showing a monotonic behavior that gives rise to magic
angles in full agreement with those of twisted bilayer graphene. Therefore,
magic angle behavior is universally found in chiral collapsed nanotubes with a
small chiral angle, giving rise to moir\'e patterns. Our approach comprises
first-principles and semi-empirical calculations of the band structure, density
of states and spatial distribution of the localized states signaled by flat
bands
Electronic conductance of twisted bilayer nanoribbon flakes
We study the transport properties of a twisted bilayer graphene flake contacted by two monolayer nanoribbons which act as leads. We analyze the conductance in terms of the spectra of the bilayer nanoribbon and the monolayer contacts. The low-energy transport properties are governed by the edge states with AB stacking. Remarkably, the electronic conductance in this energy region does not depend much on the relative position of the leads, in contrast with that of bilayer flakes with more symmetric stackings. We attribute this feature to the localization of these low-energy states in the AB edge regions of the flake, having a much smaller weight at the junctions between the flake and the nanoribbon leads.This work was partially supported by the Polish Ministry of Science and Higher Education (The “Mobility Plus” Program) and the Spanish Ministry of Economy and Competitiveness under Grant No. FIS2012-33521. E.S.M. acknowledges FONDECYT Grant 11130129
Twisted bilayer blue phosphorene: A direct band gap semiconductor
We report that two rotated layers of blue phosphorene behave as a direct band gap semiconductor. The optical spectrum shows absorption peaks in the visible region of the spectrum and in addition the energy of these peaks can be tuned with the rotational angle. These findings makes twisted bilayer blue phosphorene a strong candidate as a solar cell or photodetection device. Our results are based on ab initio calculations of several rotated blue phosphorene layers
Optical absorption spectrum of rotated trilayer graphene
Using ab initio calculations we have studied the optical linear response of different configurations of twisted trilayer graphene systems. We have found that when one of the outer layers is rotated the system shows an angle-dependent optical spectrum as its twisted bilayer counterpart; however, in this case there are two absorption peaks located in the visible range of the spectrum and one more in the intermediate infrared range for large relative rotation angles. When two layers are rotated the spectrum exhibits only two absorption peaks in the visible range revealing information about the two relative rotation angles between the layers in the structure. All these absorption peaks in the visible range shift to the intermediate infrared range for small angles