Speaker
Description
Diagrammatic Monte Carlo (DMC) is the numerical technique of summation of Feynman diagrams without approximations. Bold DMC (BDMC) is the method of self-consistent summation of the irreducible skeleton Feynman diagrams, which are used to modify the Green functions and interparticle interactions by solving the Dyson equation. Modified propagators are used again, forming a self-consistent loop that often circumvents the sign problem in many-body systems.
The DMC was applied to study the optical conductivity (OC) and mobility $\mu$ of the single-polaron problem in the Holstein and Frohlich models with linear electron-phonon interaction and the double-well model with highly nonlinear coupling to lattice displacements. The linear models were treated using a DMC method in momentum space [1,2] and a novel direct-space X-propagator method was developed for the nonlinear model. For every model, one can identify several regimes, some of which are similar across all models. The common feature of all models is the presence of nonmonotonic temperature dependence of $\mu$.
The calculation of OC and $\mu$ for systems of finite density was performed by BDMC, which has previously been used to calculate ground-state properties and ARPES of finite-density polaron systems [3,4] . A novel technique, the torn-out polarization operator method, is developed to calculate the current-current correlation function. We describe the method, prove its validity, and show first results of the doping dependence of the optical conductivity and mobility.
- A. S. Mishchenko, N. Nagaosa, G. De Filippis, A. de Candia, and V. Cataudella, Phys. Rev. Lett. 114, 146401 (2015).
- A. S. Mishchenko, L. Pollet, N. V. Prokof’ev, A. Kumar, D. L. Maslov, and N. Nagaosa, Phys. Rev. Lett. 123, 076601 (2019).
- A. S. Mishchenko, N. Nagaosa, and N. Prokof’ev, Phys. Rev. Lett. 113, 166402 (2014).
- A. S. Mishchenko, I. S. Tupitsyn, N. Nagaosa, and N. Prokof’ev, Sci. Rep. 11, 9699 (2021).