Predicting charge transport in the presence of polarons: The beyond-quasiparticle regime inSrTiO3

Abstract

In materials with strong electron-phonon (e-ph) interactions, the electrons carry a phonon cloud during their motion, forming quasiparticles known as polarons. Predicting charge transport and its temperature dependence in the polaron regime remains an open challenge. Here, we present first-principles calculations of charge transport in a prototypical material with large polarons, SrTiO3. Using a cumulant diagram-resummation technique that can capture the strong e-ph interactions, our calculations can accurately predict the experimental electron mobility in SrTiO3 between 150−300 K. They further reveal that for increasing temperature the charge transport mechanism transitions from band-like conduction, in which the scattering of renormalized quasiparticles is dominant, to a beyond-quasiparticle transport regime governed by incoherent contributions due to the interactions between the electrons and their phonon cloud. Our work reveals long-sought microscopic details of charge transport in SrTiO3, and provides a broadly applicable method for predicting charge transport in materials with strong e-ph interactions and polarons.

Ab initio electron-two-phonon scattering in GaAs from next-to-leading order perturbation theory

“…In summary, our calculations of the 2ph scattering rates and their contribution to the mobility pave the way to studying higher-order e-ph interactions and charge transport in polar materials from first principles. Together with recently proposed methods to treat charge transport in materials with polarons and stronger e-ph interactions 24 , it is clear that ab initio calculations are becoming able to investigate e-ph interactions and charge transport in a wide range of polar materials.…”

“…In materials with intermediate or strong e-ph coupling, such as oxides with low room-temperature mobility and ionic compounds (e.g., alkali halides), the e-ph interactions can lead to regimes beyond the reach of perturbation theory, including the formation of polarons 20 . This coupling regime has been investigated with diagram-resummation techniques such as the cumulant method, both analytically 21 and more recently ab initio [22][23][24] .…”

Lightly doped SrTiO3: A challenge to conventional solid state theory

“…They show that the observed temperature dependence of the effective mass removes the conflict with the Mott-Ioffe-Regel criterion and the Planck limit up to 400K, but at the highest temperatures the conflict still exists. A possible explanation of this behavior may be found in two recent works [2], [3] exploring the consequences of a strong electron-phonon interaction at these high temperatures. These authors, employing state of the art numerical techniques, are able to show that as the temperature rises beyond the Fermi temperature Landau quasiparticles evolve into polarons the mass of which is indeed increasing with temperature.…”

“…For a class of incoherent states it has been shown that the Planck limit is respected [4]. In the case of STO the incoherent state found in [2], [3] appears to violate the Planck limit, which is presumably related to the fact that "external interactions" (phonons), which are not included in the derivation of "universal bounds" [4] play the main role.…”

Long-range quadrupole electron-phonon interaction from first principles

“…Electron-phonon (e-ph) interactions are key to understanding electrical transport, nonequilibrium dynamics, and superconductivity [1]. First-principles calculations can provide microscopic insight into e-ph scattering processes and are rapidly emerging as a quantitative tool for investigating charge transport and ultrafast carrier dynamics in materials [2][3][4][5][6][7][8][9][10][11][12][13]. The typical workflow combines density functional theory (DFT) [14] calculations of the ground state and band structure with density functional perturbation theory (DFPT) [15] for phonon dispersions and e-ph perturbation potentials.…”