Afsal Thuppilakkadan

Bio: Afsal Thuppilakkadan is an academic researcher from Indian Institute of Technology Mandi. The author has contributed to research in topics: Photoionization & Ionization. The author has an hindex of 3, co-authored 5 publications receiving 27 citations.

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.

Systematic study of Coulomb confinement resonances of atoms trapped inside charged fullerenes

Abstract: An earlier work of Dolmatov et al. [Phys. Rev. A 73, 013201 (2006)] on Ne inside a charged fullerene ($\mathrm{Ne}@{\mathrm{C}}_{60}^{\mathrm{q}=\ensuremath{-}3,\ensuremath{-}5}$) has revealed the presence of two unusually large confinement resonances termed Coulomb confinement resonances (CCRs); the first CCR is narrow and the second one is broad and their origins are attributed to the presence of charge on the fullerene surface. The present work extends this study to other subshells and also to other systems such as $\mathrm{Ar}@{\mathrm{C}}_{60}^{\mathrm{q}}$ and $\mathrm{Xe}@{\mathrm{C}}_{60}^{\mathrm{q}}$ using relativistic random phase approximation, but with an aim to investigate the genesis of the CCRs. Further, a detailed analysis of these resonances within a single active electron approximation unearths an interesting difference associated with the origin of these two CCRs. The photoionized electron is temporally trapped in the ${\mathrm{C}}_{60}$ confinement well for the case of narrow resonance and in the atomic well region for the case of broad resonance. Also, the present work shows that the broad resonance can occur even for the case of $q=0$ and is demonstrated for $\mathrm{Xe}@{\mathrm{C}}_{60}^{\mathrm{q}}$ as a test case.

Dramatic Distortion of the $4d$ Giant Resonance by the $C_{60}$ Fullerene Shell

Abstract: The photoionization cross section for the endohedral Xe@C60 atom is investigated within the framework of representing the C60 by a delta-type potential. Results demonstrate that in Xe@C60, the 4d giant resonance is distorted significantly when compared with that of the isolated Xe atom. The reflection of the photoelectron waves by the C60 causes strong oscillations in the photoionization cross section resulting in the replacement of the Xe 4d giant resonance by four prominent peaks. The approximation of C60 by an infinitely thin real potential preserves reasonably well the sum rule for the 4d electrons but modifies the dipole polarizability of the 4d shell.