Roton dipole moment

TL;DR

This paper investigates the instantaneous electric dipole moment of roton excitations in superfluid helium-4, providing theoretical estimates that align with recent experimental observations of microwave resonance splitting under electric fields.

Contribution

It introduces a calculation of the roton's instantaneous dipole moment and compares it with experimental data, highlighting a new understanding of roton electric properties.

Findings

Instantaneous dipole moment of roton is non-zero.

Theoretical estimates agree with experimental resonance splitting.

Roton exhibits a fluctuating dipole moment aligned with its momentum.

Abstract

The roton excitation in the superfluid He-4 does not possess a stationary dipole moment. However, a roton has an instantaneous dipole moment, such that at any given moment one can find it in the state either with positive or with negative dipole moment projection on its momentum direction. The instantaneous value of electric dipole moment of roton excitation is evaluated. The result is in reasonable agreement with recent experimental observation of the splitting of microwave resonance absorption line at roton frequency under external electric field.