Three-dimensional topological Dirac semimetals (TDSs) are a new kind of Diracmaterials that exhibit linear energy dispersion in the bulk and can be viewedas three-dimensional graphene. It has been proposed that TDSs can be driven toother exotic phases like Weyl semimetals, topological insulators andtopological superconductors by breaking certain symmetries. Here we report thefirst transport experiment on Landau level splitting in TDS Cd3As2 singlecrystals under high magnetic fields, suggesting the removal of spin degeneracyby breaking time reversal symmetry. The detected Berry phase develops anevident angular dependence and possesses a crossover from nontrivial to trivialstate under high magnetic fields, a strong hint for a fierce competitionbetween the orbit-coupled field strength and the field-generated mass term. Ourresults unveil the important role of symmetry breaking in TDSs and furtherdemonstrate a feasible path to generate a Weyl semimetal phase by breaking timereversal symmetry.
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