Attosecond time delay in the photoionization of endohedral atoms A@C60: A probe of confinement resonances

The effects of confinement resonances on photoelectron group delay (Wigner time delay) following ionization of an atom encapsulated inside a C60 cage have been studied theoretically using both relativistic and nonrelativistic random phase approximations. The results indicate clearly the resonant character of the confinement oscillations in time delay of the 4d shell of Xe@C60 and present a most direct manifestation of Wigner time delay. These oscillations were missed in a previous theoretical investigation of Ar@C60 [Phys. Rev. Lett. 111, 203003 (2013)PRLTAO0031-900710.1103/PhysRevLett.111.203003]. © 2014 American Physical Society