Ultrafast Faraday Rotation Probe of Chiral Phonon-Polaritons in LiNbO3

TL;DR

This study demonstrates ultrafast probing of chiral phonon-polaritons in LiNbO3 using the Faraday effect, revealing a strong induced magnetic field and breaking time reversal symmetry.

Contribution

It introduces a novel method combining circularly polarized THz pulses to excite and measure chiral phonon-polaritons via ultrafast Faraday rotation.

Findings

Induced magnetic field strength of ~11 Tesla estimated.

Faraday signal flips with input polarization change.

Chiral phonon-polaritons break time reversal symmetry.

Abstract

Time reversal symmetry breaking motion of chiral phonon-polaritons in LiNbO3 is probed via the ultrafast Faraday effect. By combining a pair of perpendicularly polarized THz pulses with the right relative delay, we create a chiral THz driving field to excite chiral phonon-polaritons. The chiral atomic motion combines with the inverse Faraday effect from the circularly polarized THz pump to induce a magnetic moment field in the nonmagnetic material, LiNbO3. We attempt to quantify the strength of the magnetic field with Faraday rotation probe measurements. The direction of the Faraday signal flips when the input THz pulse is changed from left- to right-circular polarization, and we estimate a strong induced magnetic field strength of ~11 Tesla based on the Faraday rotation.