Anharmonic coupling between electrons and TO phonons in the vicinity of ferroelectric quantum critical point

TL;DR

This paper investigates how anharmonicity in TO phonons near a ferroelectric quantum critical point enables a novel electron-phonon coupling mechanism, affecting thermoelectric properties and electron-lattice dynamics.

Contribution

It introduces a new coupling mechanism between electrons and anharmonic TO phonons near ferroelectric quantum criticality, with implications for thermoelectricity and lattice dynamics.

Findings

Emergent phonon drag can significantly enhance thermoelectric conductivity.

An effective correlated electron-ion dynamics method captures local polarization effects.

Optimal conditions may surpass thermoelectric performance of PbTe.

Abstract

We explore a novel coupling mechanism of electrons with the transverse optical (TO) phonon branch in a regime when the TO mode becomes highly anharmonic and drives the ferroelectric phase transition. We show that this anharmonicity, which leads to a collective motion of ions, is able to couple electronic and lattice displacement fields. An effective correlated electron-ion dynamics method is required to capture the effect of the onset of the local electric polarization due to this collective behavior close to the quantum critical point. We identify an intermediate temperature range where an emergent phonon drag may contribute substantially to thermoelectric conductivity in this regime. We find that, under optimal conditions, this extra contribution may be larger than values achieved so far in the benchmark material, PbTe. In the last part we make a case for the importance of our results in the generic problem of anharmonic electron-lattice dynamics.