Relaxation effects in the photoionization time delay near the 3 s Cooper minimum of Ar

The discrepancy in the attosecond time delay between theory and experiment near the 3⁢𝑠 Cooper minimum (CM) of Ar is addressed. It is found that inclusion of the relaxation effects in the time delay difference between Ar 3⁢𝑠 and 3⁢𝑝 photoionization near the 3⁢𝑠 CM dramatically alters the 3⁢𝑠 time delay and brings the theory into substantial agreement with experiment using the relativistic-random-phase approximation with relaxation. The key point is that 3⁢𝑠 photoionization is dominated by interchannel coupling in this region and the interchannel coupling matrix elements were found to be considerably altered by the inclusion of relaxation. This implies that relaxation should be important for any atomic or molecular transition that is dominated by interchannel coupling.