Dai-Nam Le

We develop a first-principles approach based on maximally localized Wannier functions for the calculation of higher order multipolar response properties in crystals including dipole–quadrupole, quadrupole–quadrupole, and dipole-octupole polarizabilities. The method is based on an interpolation procedure of the electronic structure of materials, and it is formulated by extending molecular perturbation theory to periodic crystals. General symmetry considerations are used to determine relations between different components and to prove that the dipole–quadrupole polarizability vanishes in centrosymmetric systems. The approach is applied to compute and analyze the multipole–multipole polarizabilities of several representative materials, including centrosymmetric systems (bulk graphite, h-BN, MoS2, and 2H-phase WTe2) and noncentrosymmetric ones (bulk Td–WTe2 and bulk Te). The multipole–multipole polarizabilities are further related to optical gyration with specific application to Te and Td–WTe2. The proposed algorithm possesses several advantages, including conceptual simplicity, computational efficiency, and relatively low computational cost for the computation of multipolar response in materials.

Friction in atomistic systems is usually described by the classical Prandtl-Tomlinson model suitable for capturing the dragging force of a nanoparticle in a periodic potential. Here we consider the quantum mechanical version of this model in which the dissipation is facilitated by releasing heat to an external bath reservoir. The time evolution of the system is captured with the Liouville-von Neumann equation through the density matrix of the system in the Markov approximation. We examine several kinetic and dissipative properties of the nanoparticle by delineating classical vs quantum mechanical effects. We find that the Landau-Zener tunneling is a key factor in the overall reduction of the frictional dissipation when compared to the classical motion in which such tunneling is absent. Other regimes of motion, controlled by the corrugation parameter and other properties, are also found. This in-depth study analyzes the interplay between velocity, strength of interaction, and temperature to control the frictional force and provide useful guidelines for experimental data interpretation.

The phononic Casimir effect between planar objects is investigated by deriving a formalism from the quantum partition function of the system following multiscattering approach. This fluctuation-induced coupling is mediated by phonons modeled as an effective elastic medium. We find that excitations with three types of polarizations arise from the resolved boundary conditions, however the coupling is dominated by only one of these degrees of freedom due to exponential suppression effects in the other two. The obtained scaling laws and dependence on materials properties and temperature suggest effective pathways of interaction control. Scenarios of materials combinations are envisioned where the phononic Casimir effect is of similar order as the standard Casimir interaction mediated by electromagnetic fluctuations.

The Phononic Casimir effect between planar objects is investigated by deriving a formalism from the quantum partition function of the system following multiscattering approach. This fluctuation-induced coupling is mediated by phonons modeled as an effective elastic medium. We find that excitations with three types of polarizations arise from the resolved boundary conditions, however the coupling is dominated by only one of these degrees of freedom due to exponential suppression effects in the other two. The obtained scaling laws and dependence on materials properties and temperature suggest effective pathways of interaction control. Scenarios of materials combinations are envisioned where the Phononic Casimir effect is of similar order as the standard Casimir interaction mediated by electromagnetic fluctuations.

Radiative heat transfer is of great interest from a fundamental point of view and for energy harvesting applications. This is a material dependent phenomenon where confined plasmonic excitations, hyperbolicity and other properties can be effective channels for enhancement, especially in the near field regime. Materials with reduced dimensions may offer further benefits of enhancement compared to the bulk systems. Here we study the radiative heat transfer power in the family of transition metal dichalcogenide monolayers in their H- and T-symmetries. For this purpose, the electronic and optical properties computed from first-principles are used in effective models to understand the emerging scaling laws for metals and semiconductors as well as specific material signatures as control knobs for radiative heat transfer. Our combined approach of analytical modeling with properties from ab initio simulations can be used for other materials families to build a materials database for radiative heat transfer.

Radiative heat transfer is of great interest from a fundamental point of view and for energy harvesting applications. This is a material dependent phenomenon where confined plasmonic excitations, hyperbolicity and other properties can be effective channels for enhancement, especially at the near field regime. Materials with reduced dimensions may offer further benefits of enhancement compared to the bulk systems. Here we study the radiative thermal power in the family of transition metal dichalcogenide monolayers in their H- and T-symmetries. For this purpose, the computed from first principles electronic and optical properties are then used in effective models to understand the emerging scaling laws for metals and semiconductors as well as specific materials signatures as control knobs for radiative heat transfer. Our combined approach of analytical modeling with properties from ab initio simulations can be used for other materials families to build a materials database for radiative heat transfer.