Intermediate polaronic charge transport in organic crystals from a many-body first-principles approach

Abstract

Charge transport in organic molecular crystals (OMCs) is conventionally categorized into two limiting regimes − band transport, characterized by weak electron-phonon (e-ph) interactions, and charge hopping due to localized polarons formed by strong e-ph interactions. However, between these two limiting cases there is a less well understood intermediate regime where polarons are present but transport does not occur via hopping. Here we show a many-body first-principles approach that can accurately predict the carrier mobility in this intermediate regime and shed light on its microscopic origin. Our approach combines a finite-temperature cumulant method to describe strong e-ph interactions with Green-Kubo transport calculations. We apply this parameter-free framework to naphthalene crystal, demonstrating electron mobility predictions within a factor of 1.5−2 of experiment between 100 and 300 K. Our analysis reveals the formation of a broad polaron satellite peak in the electron spectral function and the failure of the Boltzmann equation in the intermediate regime.

Comparison of the canonical transformation and energy functional formalisms for ab initio calculations of self-localized polarons

“…In Fig. 3(b) we compare the low-energy polaron dispersion in the canonical transformation with ω c = 180 meV to our recent cumulant calculation in naphthalene [31]. For this optimal cutoff, the two methods give polaron band structures in quantitative agreement-both methods predict a polaron with dispersive bands and modest mass renormalization.…”

“…The calculations on naphthalene follow the same workflow, using settings and numerical details provided in Ref. [31].…”

“…We carry out a polaron band-structure calculation on naphthalene, an organic semiconductor with non-negligible polaron hopping. Electron carriers in naphthalene possess a narrow bandwidth of ∼200 meV, leading to pronounced polaron effects [31]. We Wannierize the two lowest conduction bands, and we calculate the polaron band structure using tight binding with the energies E mn in Eq.…”

“…Note that the cumulant method we used in Ref. [31] includes all phonon modes and provides accurate polaron spectral functions. However, it is a perturbative approach, which sums over all the improper Feynman diagrams where, at order n, the Fan-Migdal e-ph self-energy is repeated n times and weighted by a 1/n!…”

Strongly Correlated Ladders in K-Doped p-Terphenyl Crystals

“…Furthermore, electron–phonon coupling is sometimes important in organic materials. Based on arguments for similar organic crystalline systems, , we expect that polaron (or at least small polaron) formation, and thus charge localization, to be unlikely in the supramolecular system we study, and that coupling to Peierls phonon modes related to terphenyl–terphenyl bond distortions exerts the largest effect in transport, possibly leading to unconventional electronic behavior . A quantitative treatment of this problem, however, requires inclusion of the coupling of electrons to both Holstein , and Peierls modes, a direction we plan to address in the future.…”