Origin of the crossover from polarons to Fermi liquids in transition metal oxides

Carla Verdi,Feliciano Giustino,Fabio Caruso

doi:10.1038/ncomms15769

Abstract

Transition metal oxides host a wealth of exotic phenomena ranging from charge, orbital and magnetic order to nontrivial topological phases and superconductivity. In order to translate these unique materials properties into device functionalities these materials must be doped; however, the nature of carriers and their conduction mechanism at the atomic scale remain unclear. Recent angle-resolved photoelectron spectroscopy investigations provided insight into these questions, revealing that the carriers of prototypical metal oxides undergo a transition from a polaronic liquid to a Fermi liquid regime with increasing doping. Here, by performing ab initio many-body calculations of angle-resolved photoemission spectra of titanium dioxide, we show that this transition originates from non-adiabatic polar electron–phonon coupling, and occurs when the frequency of plasma oscillations exceeds that of longitudinal-optical phonons. This finding suggests that a universal mechanism may underlie polaron formation in transition metal oxides, and provides a pathway for engineering emergent properties in quantum matter.

Highlights

Transition metal oxides host a wealth of exotic phenomena ranging from charge, orbital and magnetic order to nontrivial topological phases and superconductivity
We show how the interplay between the dynamical screening of the electron plasma and the Frohlich electron–phonon coupling is responsible for the transition between polaronic and Fermi liquid states
The present analysis reveals that the origin of the crossover from polarons to a Fermi liquid in the angleresolved photoelectron spectroscopy (ARPES) spectra of doped TiO2 is to be found in a form of electron–phonon coupling, which we refer to as a non-adiabatic Frohlich interaction

Summary

Introduction

Transition metal oxides host a wealth of exotic phenomena ranging from charge, orbital and magnetic order to nontrivial topological phases and superconductivity. By performing ab initio many-body calculations of angle-resolved photoemission spectra of titanium dioxide, we show that this transition originates from non-adiabatic polar electron–phonon coupling, and occurs when the frequency of plasma oscillations exceeds that of longitudinal-optical phonons This finding suggests that a universal mechanism may underlie polaron formation in transition metal oxides, and provides a pathway for engineering emergent properties in quantum matter. The signature of polaronic behaviour in ARPES spectra is the appearance of satellites below the conduction band, at integer multiples of the optical phonon energy Despite its pivotal role in a broad range of technologies, the nature of the charge carriers in anatase is still controversial[17] We address these issues by calculating ARPES spectra and polaron wavefunctions entirely from first principles. We propose that the mechanism identified in this work may be universal, and applies to other oxides such as SrTiO3 and ZnO

Methods

Results

Conclusion