Singular long-wave vibronic interaction in superfluid helium: manifestation in zero-phonon line

Abstract: A theory is proposed [1] that describes the vibronic transitions in impurity atoms in superfluid helium, based on a two-fluid model of helium II. It is shown that, owing to the Archimedes’ principle, the linear vibronic interaction with low-frequency phonons in the liquid phase is singularly enhanced. As a result of such a singular increase in the vibronic interaction, a macroscopic amount of phonons with an almost zero frequency is created during the electronic transition in impurity atom, which leads to a finite broadening of the zero-phonon line (ZPL) in the optical spectrum already at the zero temperature limit. It is shown that the temperature dependence of the ZPL has a discontinuity in the derivative at the temperature =2.17 K, and above this dependence becomes linear. Theory is applied for the description of the studied in [2] temperature dependence of ZPL of the optical spectrum of the inner shell transition of the Dy atom in superfluid helium. A good agreement of the theory with experiment is achieved, taking into account, in addition to the linear vibronic interaction, the inhomogeneous broadening of ZPL, caused by slow fluctuations of the surface tension of the bubbles of the surrounding helium atoms.

[1] V.Hizhnyakov, V. Boltrushko, G. Benedek, Thermal broadening of zero-phonon line in superfluid helium, PRB, 2021.

[2] P. Moroshkin and K. Kono, Physical Review B 99, 104512 (2019).

astrophysicscondensed mattergeneral relativity and quantum cosmologyhigh energy physicsmathematical physicsclassical physicsgeneral physics

Audience: researchers in the topic

Theoretical physics seminar @ Tartu