Papers by Thakshila M.Herath
Journal of Applied Physics
We study theoretically interaction of a bilayer graphene with a circularly polarized ultrafast op... more We study theoretically interaction of a bilayer graphene with a circularly polarized ultrafast optical pulse of a single oscillation at an oblique incidence. The normal component of the pulse breaks the inversion symmetry of the system and opens up a dynamical band-gap, due to which a valley-selective population of the conduction band becomes sensitive to the angle of incident of the pulse. We show that the magnitude of the valley polarization can be controlled by the angle of incidence, the amplitude, and the angle of in-plane polarization of the chiral optical pulse. Subsequently, a sequence of a circularly polarized pulse followed by a linearly polarized femtosecond-long pulse can be used to control and probe the valley polarization created by the preceding pulse. Our protocol provides a favorable platform to design ultrafast all-optical valleytronic information processing.
Journal of Physics: Condensed Matter, 2016
The band gap of buckled graphene-like materials, such as silicene and germanene, depends on exter... more The band gap of buckled graphene-like materials, such as silicene and germanene, depends on external perpendicular electric field. Then a specially design profile of electric field can produce trapping potential for electrons. We study theoretically the energy spectrum and optical transitions for such designed quantum dots (QDs) in graphene-like materials. The energy spectra depend on the size of the QD and applied electric field in the region of the QD. The number of the states in the QD increases with increasing the size of the dot and the energies of the states have almost linear dependence on the applied electric field with the slope which increases with increasing the dot size. The optical properties of the QDs are characterized by two types of absorption spectra: interband (optical transitions between the states of the valence and conduction bands) and intraband (transitions between the states of conduction/valence band). The interband absorption spectra have triple-peak structure with peak separation around 10 meV, while intraband absorption spectra, which depend on the number of electrons in the dot, have double-peak structure.
Bulletin of the American Physical Society, Mar 2, 2015
Quantum dots in graphene-like materials THAKSHILA HERATH, VADYM APALKOV, Georgia State University... more Quantum dots in graphene-like materials THAKSHILA HERATH, VADYM APALKOV, Georgia State University -We study numerically the electron states in silicene and germanene quantum dots within the effective low energy model of silicene and germanene. The quantum dots are realize through spatial variation of perpendicular electric field, i.e., bias voltage. The energy spectra of such quantum dots are obtained for different parameters of the dots, which are the size of the dot and the strength of external electric field. For cylindrically symmetric spatial profile of electric field, the electron states of the dot are characterized by z-component of the angular momentum. Due to strong spin-orbit interactions in such buckled graphene-like materials, the states in the quantum dots have unique spin texture, which is more pronounced for germanene quantum dots. The dependence of spin polarization of electron states in the quantum dots on the strength of electric field is also obtained.
Frontiers in Optics 2013 Postdeadline, 2013
Journal of Physics: Condensed Matter, 2014
We introduce a quantum dot in topological insulator nanofilm as a bump at the surface of the nano... more We introduce a quantum dot in topological insulator nanofilm as a bump at the surface of the nanofilm. Such a quantum dot can localize an electron if the size of the dot is large enough, 5 nm. The quantum dot in topological insulator nanofilm has states of two types, which belong to two ('conduction' and 'valence') bands of the topological insulator nanofilm. We study the energy spectra of such defined quantum dots. We also consider intraband and interband optical transitions within the dot. The optical transitions of the two types have the same selection rules. While the interband absorption spectra have multi-peak structure, each of the intraband spectra has one strong peak and a few weak high frequency satellites.
We study the properties of a steplike defect on the surface of ultrathin topological insulator na... more We study the properties of a steplike defect on the surface of ultrathin topological insulator nanofilms. We calculate the reflectance of an electron from such a defect for different parameters of the nanofilm and different parameters of the defect. We show that an electron incident on a steplike defect not only produces reflected and transmitted waves but also generates the modes, which are localized at the steplike defect. Such modes result in an enhancement of electron density at the defect by ≈60%. The magnitude of the enhancement depends on the parameters of the nanofilm and the height of the step and is the largest in the case of total electron reflection.
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Papers by Thakshila M.Herath