Speaker
Description
Polaron physics remains central to understanding charge transport in materials with strong electron-phonon coupling, where quasiparticles emerge as electrons dressed by lattice excitations. The Holstein model provides the standard framework for describing small polarons, assuming harmonic phonons and linear coupling. However, this approximation breaks down in materials such as quantum paraelectrics, hydrides, and halide perovskites, where anharmonic lattice effects play a crucial role.
We have developed a continuous-time quantum Monte Carlo method formulated in the ionic displacement basis (X-Representation), which samples the perturbation expansion of the electronic imaginary-time Green's function with respect to electron hopping. The method is approximation-free and enables the treatment of arbitrary anharmonic potentials, including double-well potentials relevant to quantum paraelectrics and ferroelectrics. Moreover, it provides reliable access to the physically relevant adiabatic regime, where phonon frequencies are small compared to electron hopping, and many existing approaches become ineffective.
This talk presents high-precision calculations of ground-state polaron properties across different regimes and combinations of linear and nonlinear electron-phonon coupling, revealing strong renormalization effects in the double-well regime. By extending the method to compute the imaginary-time current-current correlation function, we also extract signatures of the optical conductivity spectrum. These results provide key insights into experimentally observable behavior and highlight the role of anharmonicity in shaping polaron dynamics in complex materials.