Abstract
Dirac materials are a large class of condensed matter systems with low-energy excitations described by the Dirac equation. Usually, Dirac-like excitations can be either collective states or band structure effects and have been discovered in systems ranging from exotic quantum fluids to crystalline materials. In the past decades, they have inspired intensive experimental and theoretical study in various realistic materials, like topological insulators and topological semimetals. Due to the unique band structure, Dirac materials can exhibit plentiful intriguing transport phenomena, like the weak anti-localization, quantum oscillations, and negative longitudinal magnetoresistance.
In this talk, I will present the quantum interference theory for both two- and three-dimensional massive Dirac fermions. First, a magnetoconductivity formula from the quantum interference effect is derived for two-dimensional massive Dirac fermions. For magnetic topological insulators, it is shown that the tiny band gap in the energy spectrum of surface states leads to a temperature-dependent Berry phase, which introduces an additional phase breaking rate for surface electrons. As a result, the quantum correction to the conductivity can display a nonmonotonic temperature dependence. A quantitative comparison with the experimental data in magnetic topological insulators confirms our theory. Furthermore, based on the quantum interference theory, a magnetoconductivity formula is also derived for three-dimensional massive Dirac fermions. It is shown that the strong competition of the multiple Cooperon channels results in an unusual crossover from positive to negative magnetoresistance, which is coincident with the experimental measurements in the Dirac semimetal Cd3As2. This work sheds light on the importance of the multi-band effect in Dirac materials.
Anyone interested is welcome to attend.