arXiv subjects

Mingran Kong

Publications and source records attributed to Mingran Kong.

3 recordsLinked to original sources

arXiv2026

Anharmonic dephasing in the electron-phonon interaction

Electron-phonon coupling has been a central topic in condensed matter physics for decades, and firstprinciples methods have demonstrated remarkable success in quantitatively capturing its role in a wide variety of physical phenomena and materials. Conventional calculations of electron-phonon coupling typically assume that phonons have infinite lifetimes, but phonons can exhibit finite lifetimes due to anharmonic phonon-phonon interactions. In this work, we derive an expression for the electron-phonon coupling scattering rates including the effects of anharmonic three-phonon interactions, which lead to phonon dephasing and finite phonon lifetimes. We also describe a first-principles implementation of this anharmonic electron-phonon coupling which can be seamlessly integrated within existing workflows for the evaluation of electron-phonon and phonon-phonon coupling interactions. Finally, we present calculations of electron-phonon scattering rates including phonon dephasing in a range of materials, and discuss the different microscopic mechanisms by which anharmonic phonons influence electron-phonon coupling. This study establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon coupling, and provides a platform to explore these effects in a wide range of materials and phenomena.

cond-mat.mtrl-sci↗

arXiv2026

Electronic conductivity in anharmonic crystals: Phonon dephasing in the electron-phonon interaction

The electron-phonon interaction underpins many material properties, for example, the conductivity of metals and the optoelectronic response of semiconductors. First-principles calculations of the electron-phonon interaction are a powerful tool to quantitatively describe many of these properties in increasingly complex materials. However, one key assumption of all calculations is that phonons have infinite lifetimes, an approximation that may break down when anharmonic phonon-phonon interactions are strong. In this work, we present a theory for the interaction of electrons with finite-lifetime phonons experiencing dephasing. Using a first-principles implementation of the theory, we find that anharmonic dephasing dramatically enhances electron-phonon scattering rates in metallic MgB2. Microscopically, phonon-phonon interactions create new scattering channels that increase the phase space available for electron-phonon scattering. As a result, anharmonic dephasing strongly suppresses conductivity in MgB2, bringing the calculated values substantially closer to experiment within the Boltzmann transport equation framework. This example establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon scattering, and the microscopic mechanism suggests that anharmonic dephasing could play an important role in the conductivity of many metals. More broadly, our theory and first-principles implementation of anharmonic dephasing in the electron-phonon interaction provides a solid foundation to explore this regime in other materials.

cond-mat.mtrl-sci↗

arXiv2022

A comprehensive study of complex non-adiabatic exciton dynamics in MoSi$_2$N$_4$

Excitons, which are composite boson quasi-particles composed of bound electrons and holes, have many fascinating properties and great potential in practical applications. Though experimental studies on exciton dynamics are well-developed, the ab initio simulation ones still remain vacant until two years ago. Here, we apply the density functional theory (DFT) and many-body perturbation theory (MBPT) on 2D MoSi$_2$N$_4$ to study its exciton-related physics and non-adiabatic ultrafast exciton dynamics theoretically and numerically for the first time. We calculate the photoluminescence (PL) spectra with final states as bright excitons, yet lots of them are contributed by the dark ones, and the results match the experimental ones perfectly. We also study the dark-exciton-involved processes, which were barely studied in the past but dominate in many physical processes, and obtain several main results like: (i) High scattering rates over the whole Brillouin zone (BZ) within the order of magnitude from 10$^{-2}$ fs$^{-1}$ to 10$^{-1}$ fs$^{-1}$; (ii) Thorough analysis for the dynamics of the dark excitons at $Λ$ valley, which have negative effective mass and the highest scattering rate among several exciton states; (iii) Simulate the time-resolved evolution of the excitons after photo-excitation with the real-time Boltzmann transport equation (rt-BTE) techniques, in which process excitons at K/K' valley play an important role; (iv) Exciton dynamics with spin-valley locking at K/K' valley are also discussed here; (v) A new approach is proposed for modulating the non-adiabatic effects for excitons, accompanied by a chiral phonon absorption/emission, by tuning the chirality of the external circularly polarized light. All the results show that the 2D material MoSi$_2$N$_4$ is an ideal platform to study the exciton-involved physics and has great application value.

cond-mat.mtrl-sci↗