RKKY Interaction in Disordered Graphene

We investigate the effects of nonmagnetic disorder on the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction in graphene by studying numerically the Anderson model with on-site and hopping disorder on a honeycomb lattice at half filling. We evaluate the strength of the interaction as a function of the distance R between two magnetic ions, as well as their lattice positions and orientations. In the clean limit, we find that the strength of the interaction decays as 1/R^3, with its sign and oscillation amplitude showing strong anisotropy. With increasing on-site disorder, the mean amplitude decreases exponentially at distances exceeding the elastic mean free path. At smaller distances, however, the oscillation amplitude increases strongly and its sign changes on the same sublattice for all directions but the armchair direction. For random hopping disorder, no sign change is observed. No significant changes to the geometrical average values of the RKKY interaction are found at small distances, while exponential suppression is observed at distances exceeding the localization length.Comment: 4+\epsilon\ pages, 5 figure

RKKY Interactions in Graphene: Dependence on Disorder and Gate Voltage

We report the dependence of Ruderman-Kittel-Kasuya-Yoshida\,(RKKY) interaction on nonmagmetic disorder and gate voltage in grapheme. First the semiclassical method is employed to reserve the expression for RKKY interaction in clean graphene. Due to the pseudogap at Dirac point, the RKKY coupling in undoped grapheme is found to be proportional to $1/R^3$. Next, we investigate how the RKKY interaction depends on nonmagnetic disorder strength and gate voltage by studying numerically the Anderson tight-binding model on a honeycomb lattice. We observe that the RKKY interaction along the armchair direction is more robust to nonmagnetic disorder than in other directions. This effect can be explained semiclassically: The presence of multiple shortest paths between two lattice sites in the armchair directions is found to be responsible for the reduceddisorder sensitivity. We also present the distribution of the RKKY interaction for the zigzag and armchair directions. We identify three different shapes of the distributions which are repeated periodically along the zigzag direction, while only one kind, and more narrow distribution, is observed along the armchair direction. Moreover, we find that the distribution of amplitudes of the RKKY interaction crosses over from a non-Gaussian shape with very long tails to a completely log-normal distribution when increasing the nonmagnetic disorder strength. The width of the log-normal distribution is found to linearly increase with the strength of disorder, in agreement with analytical predictions. At finite gate voltage near the Dirac point, Friedel oscillation appears in addition to the oscillation from the interference between two Dirac points. This results in a beating pattern. We study how these beating patterns are effected by the nonmagnetic disorder in doped graphene

Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer

The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show a synthesis process for Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> alloy using sulfurization of super-cycle atomic layer deposition Mo<inf>1-x</inf>W<inf>x</inf>O<inf>y</inf>. Various spectroscopic and microscopic results indicate that the synthesized Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> alloys have complete mixing of Mo and Watoms and tunable band gap by systematically controlled composition and layer number. Based on this, we synthesize a vertically composition-controlled (VCC) Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> multilayer using five continuous super-cycles with different cycle ratios for each super-cycle. Angle-resolved X-ray photoemission spectroscopy, Raman and ultraviolet-visible spectrophotometer results reveal that a VCC Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> multilayer has different vertical composition and broadband light absorption with strong interlayer coupling within a VCC Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> multilayer. Further, we demonstrate that a VCC Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> multilayer photodetector generates three to four times greater photocurrent than MoS<inf>2</inf>-and WS<inf>2</inf>-based devices, owing to the broadband light absorption. © 2015 Macmillan Publishers Limitedopen1