Juby George

Bio: Juby George is an academic researcher from University of Hyderabad. The author has contributed to research in topics: Dislocation & Photoionization. The author has an hindex of 2, co-authored 7 publications receiving 16 citations. Previous affiliations of Juby George include Indian Institute of Technology Madras.

Photoionization of atomic krypton confined in the fullerene C60

Abstract: The combined effects of interchannel coupling, relativistic interactions and endohedral confinement on the photoionization of atomic Kr are studied. The confinement of the Kr atom placed at the centre of the C60 cage is modelled by placing the atom inside an annular spherical potential. Cross sections for the photoionization and angular distribution of photoelectrons from the 4p, 4s, 3d and 3p subshells are reported within the framework of the relativistic-random-phase approximation.

Quantum calculations for the effects of dislocations on channeling and channeling radiation

Abstract: The channeling process in a crystal bent by dislocations is considered. The Schrodinger equation for the channeled particle motion is separated between longitudinal and transverse parts. The transverse potential and the frequency of channeling radiation in the perfect channel and the two regions of dislocation affected channels are calculated. The corresponding wave functions for the transverse and longitudinal motions are also calculated. In this work, we specifically investigate the effects of longitudinal motion of the particle on the dechanneling parameter and the frequency. The continuity of wave functions and their derivatives is used at the three boundaries and reflection and transmission coefficients are found using these boundary conditions. Finally, we consider the two cases of maximum and minimum dechanneling probabilities.

Effects of dislocations on electron channeling.

Abstract: The phenomenon of electron channeling in a crystal affected by dislocations is considered. Earlier we had considered the quantum aspects of the positron channeling in a crystal bent by dislocations where the effects of longitudinal motion of the particle were also considered along with the transverse motion. In this paper, the effective potential for the electron case is found for the two regions of dislocation-affected channel. There is considerable shift in the potential minima due to dislocations. The frequency and the corresponding spectrum of the channeling radiation due to electrons channeling through the perfect channel and the two regions of dislocation-affected channels are calculated. The spectral distribution of radiation intensity changes with the parameters of dislocation. The continuity of wavefunctions and their derivatives is used at the three boundaries and the reflection and transmission coefficients are found using these boundary conditions in the same way as in the positron case.

Effects of hypersonic field and anharmonic interactions on channelling radiation

Abstract: The effects of a hypersonic field on positron channelling radiation are considered. Anharmonic effects of the transverse potential induced by these longitudinal fields are incorporated and the wavefunction of the planar channelled positron is found by the solution of Dirac equation under the resonant influence of hypersound. An expression for the resonant frequency is estimated. The transition probabilities and the intensity of the channelling radiation are also calculated. It is found that the anharmonic effects change the spectral distributions considerably.

Effects of dislocations on channeling radiation from a periodically bent crystal.

Abstract: In this paper the effects of dislocations on the positron channeling in a periodically bent crystal are studied. We begin with the unified treatment of the longitudinal and transverse motion of the particle. We then separate out the Schrodinger equation into longitudinal and transverse motions. The variation in effective potential and frequency in the different regions of dislocation affected channels is found. The wavefunctions of positrons channeled in the perfect and the dislocation affected channels are found and the channeling and dechanneling probabilities are calculated. The angular and spectral distributions of radiation intensity are calculated and compared with those of normal channeling. The calculations are carried out with varying values of dislocation density and varying undulator wavelength.

Confinement induced binding of noble gas atoms.

Abstract: The stability of Ngn@B12N12 and Ngn@B16N16 systems is assessed through a density functional study and ab initio simulation. Although they are found to be thermodynamically unstable with respect to the dissociation of individual Ng atoms and parent cages, ab initio simulation reveals that except Ne2@B12N12 they are kinetically stable to retain their structures intact throughout the simulation time (500 fs) at 298 K. The Ne2@B12N12 cage dissociates and the Ne atoms get separated as the simulation proceeds at this temperature but at a lower temperature (77 K) it is also found to be kinetically stable. He-He unit undergoes translation, rotation and vibration inside the cavity of B12N12 and B16N16 cages. Electron density analysis shows that the He-He interaction in He2@B16N16 is of closed-shell type whereas for the same in He2@B12N12 there may have some degree of covalent character. In few cases, especially for the heavier Ng atoms, the Ng-N/B bonds are also found to have some degree of covalent character. But the Wiberg bond indices show zero bond order in He-He bond and very low bond order in cases of Ng-N/B bonds. The energy decomposition analysis further shows that the ΔEorb term contributes 40.9% and 37.3% towards the total attraction in the He2 dimers having the same distances as in He2@B12N12 and He2@B16N16, respectively. Therefore, confinement causes some type of orbital interaction between two He atoms, which akins to some degree of covalent character.

On the possibility of considering the fullerene shell C60 as a conducting sphere

Abstract: Abstract The dynamical and static dipole polarizabilities of the C 60 molecule have been calculated on the basis of the experimental data on the cross section of the fullerene photoabsorption. It has been shown that the fullerene shell in the static electric field behaves most likely as a set of separate carbon atoms rather than as a conducting sphere.

Electronic structure and dynamics of confined atoms

Abstract: Confined atomic systems are of great importance owing a multitude of possible applications in various areas of science and technology. Of particular interest are atoms encaged in the $$\hbox {C}_{{60}}$$ molecule, $$\hbox {A}@\hbox {C}_{{60}}$$ , since the near-spherical symmetry of $$\hbox {C}_{{60}}$$ simplifies theoretical studies, and the stability of $$\hbox {C}_{{60}}$$ renders it amenable to experimental examination. A review of investigations of the electronic structure and dynamics of $$\hbox {A}@\hbox {C}_{{60}}$$ is presented in this manuscript focusing on developments in the last decade. Addressed mainly are how the confinement affects electronic structure properties such as ionization potentials, localization of atomic electrons, Shannon entropy, correlation effects, relativistic interactions, and others. In the area of dynamics, photoionization and e- $$\hbox {A}@\hbox {C}_{{60}}$$ scattering are reviewed and summarized, and the major effects of confinement on the dynamical properties, e.g., confinement resonances, hybridization, Wigner time delay, are delineated.

Study of resonances in the photoionization of Ar@C 60 and C 60

Abstract: The static-exchange method is applied to investigate photoionization of a confined system, Ar@C60. The realistic confinement potential employed in the present work explicitly includes the position of each carbon atom in the C60, which is a considerable improvement over methods to address the structure and photo dynamics of a confined system where the carbon shell is modelled by a spherically symmetric model potential. In the present study, photoionization from the deepest of the valence shells of C60 and Ar with ag symmetry is considered. There is a one-to-one correspondence between resonances that appear in the Ar@C60 system when the hole is in the 3s of the Ar, when the hole is in the C60 shell, or when the hole is in a free C60 system. Encapsulation of the Ar atom leads to some differences in the shapes and shifts in the energies of the resonant features in the cross-sections. However the qualitative features of the resonant state wave functions are very similar in the corresponding resonances of Ar@C60 and C60.

Photoionization phase shift and Wigner time delay of endohedrally confined atoms using transient phase methods

Abstract: In contrast to the conventional finite difference methods, two transient phase methods have been effectively used in the present work to directly compute the photoionization phase shift and Wigner time delay of confined atoms (A@C60) in the single-active electron (SAE) approximation. The different phase methods: (A) employing logarithmic derivatives at shell boundaries, and (B) Born approximation are verified with the help of well-established finite difference methods in SAE approximation and sophisticated many-electron techniques. In this work, confinement oscillations on the dipole phase and photoelectron group delay following ionization from 1s subshell of H@C60, 3p subshell of Ar@C60 and 5p subshell of Xe@C60 are analyzed. The comparison with many-body calculation shows that the features in the time delay of a confined system are governed mainly by the effects of screening apart from that due to the external potential. A systematic study and comparison of the results from phase methods and many-electron techniques indicate that these techniques can be effectively used in the analysis of photoionization phase shift and time delay in confined atoms.