Prabath Hewageegana

University of Kelaniya · Department of Physics

We predict the fundamentally fastest, ultrafast optical currents in monolayer hexagonal Boron Nitride (h-BN) by a circularly-polarized single-oscillation optical pulse. The femtosecond currents in gapped graphene and transition metal dichalcogenides have been discussed. However, the extension of the gapped graphene model for the large bandgap (∼5eV...

We theoretically study the interaction of an ultrafast intense circularly polarized optical pulse with monolayer hexagonal Boron Nitride (h-BN). Such a strong pulse redistributes electrons between the bands and generates a valley-selective conduction band population. The mechanism of producing fundamentally fastest valley polarization in this monol...

We study the importance of taking the nonlocal effects in optical response of metals into account for accurate determination of optical properties of nanoplasmonic structures. When we consider bulk materials, to explain the optical properties, it is sufficient to take only the temporal dispersion into account. But when it comes to very small struct...

Abstract􀂲􀀳􀁈􀁕􀀃 􀁆􀁄􀁓􀁌􀁗􀁄􀀃 􀁈􀁑􀁈􀁕􀁊􀁜􀀃 􀁘􀁖􀁄􀁊􀁈􀀃 􀁌􀁑􀀃 􀁄􀁑􀁜􀀃 􀁆􀁒􀁘􀁑􀁗􀁕􀁜􀀃 􀁌􀁖􀀃 􀁈􀁛􀁓􀁒􀁑􀁈􀁑􀁗􀁌􀁄􀁏􀁏􀁜􀀃 􀁌􀁑􀁆􀁕􀁈􀁄􀁖􀁌􀁑􀁊􀀃 􀁚􀁌􀁗􀁋􀀃 􀁗􀁋􀁈􀁌􀁕􀀃 􀁇􀁈􀁙􀁈􀁏􀁒􀁓􀁐􀁈􀁑􀁗􀀑􀀃 􀀤􀁖􀀃 􀁄􀀃 􀁕􀁈􀁖􀁘􀁏􀁗􀀏􀀃 􀁗􀁋􀁈􀀃 􀁆􀁒􀁘􀁑􀁗􀁕􀁜􀂶􀁖􀀃􀁇􀁈􀁓􀁈􀁑􀁇􀁈􀁑􀁆􀁈􀀃􀁒􀁑􀀃􀁗􀁋􀁈􀀃􀁉􀁒􀁖􀁖􀁌􀁏􀀃􀁉􀁘􀁈􀁏􀁖􀀃􀁉􀁒􀁕􀀃􀁈􀁑􀁈􀁕􀁊􀁜􀀃􀁊􀁈􀁑􀁈􀁕􀁄􀁗􀁌􀁒􀁑􀀃􀁌􀁖􀀃􀁄􀁏􀁖􀁒􀀃 􀁌􀁑􀁆􀁕􀁈􀁄􀁖􀁌􀁑􀁊􀀃 􀁗􀁕􀁈􀁐􀁈􀁑􀁇􀁒􀁘􀁖􀁏􀁜􀀃 􀁆􀁕􀁈􀁄􀁗􀁌􀁑􀁊􀀃 􀁈􀁆􀁒􀁑􀁒􀁐􀁌􀁆􀀃 􀁄􀁑􀁇􀀃 􀁈􀁑􀁙􀁌􀁕􀁒􀁑􀁐􀁈􀁑􀁗􀁄􀁏􀀃 􀁆􀁒􀁑􀁆􀁈􀁕􀁑􀁖􀀑􀀃 􀀷􀁕􀁒􀁓􀁌􀁆􀁄􀁏􀀃 􀁆􀁒􀁘􀁑􀁗􀁕􀁌􀁈􀁖􀀃 􀁕􀁈􀁆􀁈􀁌􀁙􀁈􀀃 􀁆􀁒􀁑􀁖􀁌􀁇􀁈􀁕􀁄􀁅􀁏􀁈􀀃 􀁄􀁐􀁒􀁘􀁑􀁗􀀃 􀁒􀁉􀀃 􀁖􀁒􀁏􀁄􀁕􀀃 􀁕􀁄􀁇􀁌...

Twin paradox is discussed in different space-times

Effects of the Cosmological constant on the energy momentum tensor

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 insulat...

This work investigates the nature of technological development and the viability of applying an evolutionary approach to the early development of iron production in Sri Lanka. The main objective of this paper is to use modern techniques in the fields of Physics and Engineering to investigate the wind-driven furnace used in early iron and steel prod...

We study the optical properties of quantum dots in topological insulator nanofilm. The quantum dots have cylindrical shape and are realized as a region of larger thickness of the nanofilm. The energy spectra of quantum dots depend on their size and the thickness of nanofilm. There are two types of optical transitions in topological insulator quantu...

Ultrathin topological insulator nanofilm with a step-like defect, which divides two regions of nanofilm with different thicknesses, is considered. Electron, propagating along the nanofilm surface, is reflected from the step. We calculate the reflectance of such electron for different parameters of the nanofilm and different parameters of the defect...

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 w...

We develop a method for calculating transverse static polarizability (per unit length) of a bulk nanowire by taking in to account the temporal and spatial dispersion. To describe these phenomena, we developed analytical theory based on local random- phase approximation and plasmon pole approximation. Our theory is very general in the sense that it...

A sphere comprising a special kind of matter, electrically counterpoised dust in which all the elastic forces have been cancelled out, has been considered. A static spherically symmetric solution to Einstein's field equations has been found using a new set of boundary conditions. In introducing these new boundary conditions, we assume that the radi...

We develop a method for calculating the polarizability of a spherical nano particle by taking in to account the temporal and spatial dispersion where dispersion due to the Landau damping. To describe these phenomena, we developed analytical theory based on local random-phase approximation. Our theory is very general in the sense that it can be appl...

A small-scale experimental salinity-gradient solar pond, which will be utilized for the research and development in harnessing solar energy for desalination of seawater and generation of electricity, has been constructed. The pond has effective length, width and depth of 3.0 m, 2.0 m and 2.0 m, respectively, covering a volume capacity of 12.0 m 3....

A theoretical model of thundercloud charge separation is presented. The model assume that moisture in the updraft moving as a stream with uniform velocity condenses into particles of graupel in reaching cooler regions of the atmosphere. Falling graupels acquire a negative charge by shedding the inductive positive charge which is carried away by the...

Localized optically-nonlinear photoelectron emission from metal (silver) nanostructures under two-pulse emission has been developed for relatively low energy. For two-photon emission from random metal nanostructures, it has been shown that the coherent control allows one to move nanosize hot spots whose positions are controllable on a nanometer sca...

Graphene is a layer of crystalline carbon that just one atom thick (Novoselov et al. 2004). Graphene is a two-dimensional crystal with a honeycomb structure. The crystalline structure of graphene results in a very unique energy dispersion law (Wallace 1947). Namely, the low-energy excitations are described by the Dirac-Weyl equations for massless r...

Due to Klein’s tunneling the electronic states of a quantum dot in graphene have finite widths and an electron in quantum dot has a finite trapping time. This property introduces a special type of interdot coupling in a system of many quantum dots in graphene. The interdot coupling is realized not as a direct tunneling between quantum dots but as c...

The possibility of enhancement of sensitivity of quantum well photodetectors by adding metallic diffraction coating on top of the dielectric layer of photodetectors is studied. With the grating the spatial distribution of the intensity of electromagnetic wave within the active region of the photodetector is highly non-uniform with the intensity var...

We study theoretically an enhancement of the intensity of mid-infrared light transmitted through a metallic diffraction grating. We show that for s-polarized light the enhancement of the transmitted light is much stronger than for p-polarized light. By tuning the parameters of the diffraction grating, the enhancement of the transmitted light can be...

We study theoretically a localized state of an electron in a graphene quantum dot with a sharp boundary. Due to Klein’s tunneling, the “relativistic” electron in graphene cannot be localized by any confinement potential. In this case the electronic states in a graphene quantum dot become resonances with finite trapping time. We consider these reson...

We report our theoretical study of the effect of metallic diffraction grating on the sensitivity of quantum dot photodetectors in terahertz frequency. We have found that the effect of diffraction grating is much stronger for s-polarization than for p-polarization. For s-polarization the sensitivity of photodetectors can be enhanced by metallic diff...

We study theoretically the enhancement of the incident light transmitted through the diffraction grating. We are interested in the mid-infrared frequency range, corresponding to the intraband absorption by quantum dots. We show that for the s-polarized light the enhancement is much stronger than for p-polarized light. By tuning the parameters of th...

We theoretically study the effect of random resonators on the conversion efficiency of fundamental mode propagating through disordered nonlinear dielectric film. Only resonators with double-resonant properties, i.e., which can trap both the fundamental and second harmonic modes, contribute to local generation of the second harmonic light of high in...

"There is plenty of room at the bottom." This bold and prophetic statement from Nobel laureate Richard Feynman back in 1950s at Cal Tech launched the Nano Age and predicted, quite accurately, the explosion in nanoscience and nanotechnology. Now this is a fast developing area in both science and technology. Many think this would bring the greatest t...

We predict that nonlinear ultrafast electron photoemission by strong optical fields and, potentially, other nonlinear optical responses of metal nanostructures significantly depend on the absolute (carrier–envelope) phase of excitation pulses. Strong enhancement of the local optical fields produces these responses at excitation intensities lower by...

This paper discusses the use of plasmonic nanostructured systems as nanoantennas for photodetection. Even though semiconductors and their heterostructures have many useful properties and widely used in photodetection, their electron density is very small compared to that of metals and, therefore, they have low absorption cross sections. The idea of...

We theoretically show that two-photon coherent control yields electron photoemission from metal nanostructures localized in nano-size hot spots whose positions are controllable on nanometer scale, in agreement with recent experiments. We propose to use silver V-shapes as tailored nanoantennas for which the position of the coherently-controllable ph...

We theoretically show that two-photon coherent control yields electron photoemission from metal nanostructures that is localized in nanosize hot spots whose positions are controllable on a nanometer scale, in agreement with recent experiments. We propose to use silver V-shapes as tailored nanoantennas for which the position of the coherently contro...