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Marfoua, Brahim,Hong, Jisang Elsevier 2019 Physica E, Low-dimensional systems & nanostructure Vol.111 No.-
<P><B>Abstract</B></P> <P>Using the electronic band structure of the optimized monolayer and bilayer As<SUB>1-x</SUB>P<SUB>x</SUB> structure calculated through the DFT calculation a comprehensive study on the electronic transport properties based on the Boltzmann transport theory are investigated within the respect of the constant relaxation time approximation τ. The Seebeck coefficient of the monolayer As<SUB>x</SUB>P<SUB>1-x</SUB> system has a larger value than the bilayer system and shows no anisotropic behavior along the armchair and zigzag directions while we found a higher electrical conductivity along the armchair direction in both mono and bilayer structures. A similar behavior was found in the electronic contribution to the thermal conductivity and this was understood from the Weidmann–Franz law. We also found that the power factor had a larger value along the armchair direction than the zigzag direction. Besides, in monolayer system, the p-type As<SUB>0.75</SUB>P<SUB>0.25</SUB> alloy showed a highest power factor while the n-type bilayer As<SUB>0.75</SUB>P<SUB>0.25</SUB> alloy system displayed a highest power factor. Thus, we suggest that the thermoelectric property can be improved in alloy system compared with the pristine phosphorene and arsenene layer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated the thermoelectric property of mono and bilayer layer As<SUB>1_x</SUB>P<SUB>x</SUB> alloy systems. </LI> <LI> The Seebeck coefficient had no anisotropic behavior along ZZ and AC directions for both mono and bilayer systems. </LI> <LI> The Seebeck coefficient was higher in the monolayer system than the bilayer system. </LI> <LI> Electrical conductivity shows an anisotropic behavior along ZZ and AC-directions in both mono and bilayer As<SUB>1_x</SUB>P<SUB>x</SUB> systems. </LI> <LI> We suggest that the alloy structure may show better TE performance than the pristine phosphorene and arsenene layer. </LI> </UL> </P>
Magnetic Anisotropy of Pd/Co/Pd Ultrathin Film: Interface Vacancy Defect and O Diffusion Effect
Brahim Marfoua,Jisang Hong 한국자기학회 2021 Journal of Magnetics Vol.26 No.3
Using first principles calculation, we investigated the magnetic anisotropy of Pd/Co/Pd ultrathin film. Here, we explored the magnetic anisotropy of pristine Pd/Co/Pd ultrathin film and also interface vacancy defect (Pd or Co) and the oxygen diffusion as well. No substantial change in the magnetic moment is found in the vacancy defect and also in the O diffusion structure relative to the pristine system. We found that the pristine Pd/Co/Pd system has a perpendicular magnetic anisotropy of 1.37 meV/cell. This perpendicular magnetic anisotropy decreased to 0.46 meV/cell in Pd vacancy defect and it became 0.56 meV/cell in Co vacancy defect. We also obtained similar magnetic anisotropy energy of 0.52 meV/cell in the O impurity system. Although the vacancy defect and O impurity system exhibited a similar magnetic anisotropy, we found that this feature originated from different spin-orbit coupling effect which is sensitive to the sample preparation condition.
Valley splitting and enhanced anomalous Hall effect in Mn impurity doped WS₂/CrGeSe₃ heterostructure
Brahim Marfoua,Jisang Hong 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Valleytronics (valley-dependent electronics) is attracting extensive research effort for next generation potential device applications [1-3]. Mostly, the lifting of valley degeneracy was achieved by the incorporation of the magnetic layer induced the proximity effect or the magnetic impurity doping effect. However, it is rare to find reports regarding the valley splitting induced by impurity doping combined with the proximity effect. Thus, we investigated the possibility of enhancing the valley splitting and anomalous Hall conductivity by the combination of two methods in WS2/CrGeSe<sub>3</sub> heterostructure. In the pure WS2/CrGeSe<sub>3</sub> heterostructure, we obtained a small valley splitting of 1 meV at K<SUP>+</SUP> and K<SUP>-</SUP> valleys due to the weak hybridization between the WS2 and CrGeSe<sub>3</sub> layers. However, we obtained a large valley splitting of 68 meV in the Mn impurity doped WS2/CrGeSe<sub>3</sub> heterostructure owing to the Mn doping effect and also the K valley dependent proximity effect. Consequently, this led to a sizable difference in the out-of-plan Berry curvature. We obtained anomalous Hall conductivity (AHC) of 110 S/cm in the Mn doped WS2/CrGeSe<sub>3</sub> system, and this is 20 times larger than that found in the pristine WS2/CrGeSe<sub>3</sub> heterostructure. Our results may provide a new platform through the combination of the two approaches for potential valleytronics applications.
Electric field dependent valley polarization in 2D ferromagnetic WSe₂/CrSnSe₃ heterostructure
Brahim Marfoua,Jisang Hong 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Along with the traditional charge and spin degree of freedom physical quantities, another physical quantity namely valley state has been introduced as a new degree of freedom that can be utilized for future quantum information storage devices [1]. The valleytronics (valley-dependent electronics) in van der Waals two-dimensional (2D) heterostructures is receiving extensive research efforts. Thus, we investigated the electric field-induced valley polarization in the WSe<sub>2</sub>/CrSnSe<sub>3</sub> heterostructures by varying the stacking order. The heterostructure shows indirect band gaps of 270 and 330 meV in the two most stable structures. The WSe<sub>2</sub>/CrSnSe<sub>3</sub> heterostructure displays a ferromagnetic ground state with out-of-plane anisotropy (0.02 meV) in one stable stacking (S-1) while a small in-plane anisotropy (-0.01 meV) is found in other stacking (S-2). The Curie temperature is slightly enhanced to 73 K compared to the monolayer CrSnSe<sub>3</sub>. We have found the valley splitting of 4 meV in S-1whereas it became 9 meV in the S-2 system. The valley splitting is further enhanced if an electric field is applied from CrSnSe<sub>3</sub> to the WSe<sub>2</sub> layer whereas it is suppressed in the reversed electric field. Particularly, the S-2 structure shows a giant valley splitting of 67 meV at an electric field of 0.6 V/Å. We attribute this electric field-dependency to the dipolar effect. Overall, our findings may imply that the WSe<sub>2</sub>/CrSnSe<sub>3</sub> heterostructure can be a potential structure for obtaining a giant valley splitting.
Optical Properties of a Two-Dimensional GeTe Layer
Brahim Marfoua,홍지상 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.3
Using the first principles calculations, we explored the optical properties of the two-dimensional -GeTe structure. The 2D monolayer -GeTe had an indirect band gap of 1.79 eV, and that indirect band gap was still observed in the bilayer although the band gap had decreased to 0.61 eV. We found that the optical band gap was much larger than the electrical band gap, which was due to the indirect band gap feature of the 2D -GeTe system. In both systems, we found a very large refractive index in the visible range. Particularly, the bilayer system had a refractive index larger than 2.5 for blue light. Furthermore, the bilayer structure was found to have a larger reflectivity at ultraviolet frequencies. Consequently, we propose that the bilayer -GeTe film can be utilized for potential optical device applications.