Field-driven phase transition and magneto-optical properties in topological Dirac semimetals

Abstract: Three-dimensional topological Dirac semimetals (TDSs) are a new kind of Dirac materials that exhibit linear energy dispersion in the bulk and can be viewed as three-dimensional graphene [1-3]. It has been proposed that TDSs can be driven to other exotic phases like Weyl semimetals, topological insulators and topological superconductors by breaking certain symmetries. In this talk, I will first report the Landau level splitting in TDS Cd3As2 single crystals under high magnetic fields (up to 60T), which suggests the removal of spin degeneracy by breaking time reversal symmetry [1]. The detected Berry phase develops an evident angular dependence and possesses a crossover from nontrivial to trivial state under high magnetic fields, a strong hint for a fierce competition between the orbit-coupling and the field-generated mass term (Figure 1). Then, I will briefly review our recent progress in chiral anomaly by showing exclusively new approaches to detect the chiral anomaly and the related valley transport in ultra-high mobility Cd3As2 Dirac semimetal [4]. Three independent evidences including the E∙B-generated magneto-optical Kerr effect, the negative MR, and the valley transport, are provided as a direct and convincing experimental identification for the chiral anomaly in crystals. Finally, I would like to talk about the magneto-optical measurements in Cd3As2/ZrTe5 Dirac semimetals and some exciting transport measurements under ultra-high magnetic field [5, 6], in which a striking topological phase transition takes place (around 30 T), i.e., the dynamical mass generation. The Dirac electron spontaneously acquires a Dirac mass due to electron-electron interactions. These transitions also manifest themselves as spin density waves in both first and zeroth Landau levels. Our study presents the very first example of the dynamical mass generation phenomenon occurring in three-dimensional massless Dirac fermions in condensed matter physics.