Density functional perturbation theory for gated two-dimensional heterostructures: Theoretical developments and application to flexural phonons in graphene

Abstract

The ability to perform first-principles calculations of electronic and vibrational properties of twodimensional heterostructures in a field-effect setup is crucial for the understanding and design of next-generation devices. We present here an implementation of density functional perturbation theories tailored for the case of two-dimensional heterostructures in field-effect configuration. Key ingredients are the inclusion of a truncated Coulomb interaction in the direction perpendicular to the slab and the possibility of simulating charging of the slab via field-effects. With this implementation we can access total energies, force and stress tensors, the vibrational properties and the electronphonon interaction. We demonstrate the relevance of the method by studying flexural acoustic phonons and their coupling to electrons in graphene doped by field-effect. In particular, we show that while the electron-phonon coupling to those phonons can be significant in neutral graphene, it is strongly screened and negligible in doped graphene, in disagreement with other recent firstprinciples reports. Consequently, the gate-induced coupling with flexural acoustic modes would not be detectable in transport measurements on doped graphene.

Mobility of two-dimensional materials from first principles in an accurate and automated framework

“…We note that the way doping is induced can be important. An example is the gate-induced coupling to flexural phonons in graphene 29,75 , related to a broken mirror symmetry with respect to the graphene plane. However, we do not expect such effects to be significant for the subset of materials studied here.…”

“…B. Phonons and EPC calculationsPhonons are computed using the recent implementation of DFPT for gated 2D heterostructures29 in Quantum ESPRESSO 87,88 (QE). This development includes two important modifications: i) a cutoff of the Coulomb 1.00 0.75 0.50 0.25 0.00 0.25 0.50 q x (bohr 1 ) Irreducible phonon momenta q ∈ Q (in red, those actually computed via DFPT), and all relevant phonons (in light blue) that can be obtained from the latter by symmetry transformations.…”

Electron-phonon properties, structural stability, and superconductivity of doped antimonene

“…An accurate description of electrons coupling with out-of-plane phonon modes is presented in Ref. 60 for doped graphene, where it is also shown, that the contribution from ZA mode is negligible. Optical phonons, as we show below, have a minor effect on the electron-phonon coupling and T c .…”

Prediction of a Large-Gap and Switchable Kane-Mele Quantum Spin Hall Insulator

“…Now we discuss the mechanical stability of the monolayer. We compute phonon dispersions using 2D DFPT [28,29] including SOC and the correct 2D LO-TO asymptotics [30] (see Supplemental Material [12]); the stability of the monolayer is confirmed by the absence of imaginary frequencies. Interestingly, the zero-temperature centrosymmetric phase is promoted by the presence of KM-type SOC.…”