Observation of Magic Angle Effectin Angular Dependence of Magnetoresistance of ZrTe5 in the Quantum Limit*

We report the discovery of sharp, anomalous dips in the angular dependence of magnetoresistance in ZrTe5 single crystals. These dips occur at fixed “magic angles” once the magnetic field passes the quantum limit. The magic angles correspond to commensurate angles where the field direction connecting neighboring atoms in the lattice, reminiscent of “Lebed’s Magic Angles” found in the organic Bechgaard salts (TMTSF)₂X. Unlike the Bechgaard salts, a quasi-1D open fermi surface is absent in ZrTe5. In contrast, it has a closed ellipsoidal Fermi surface well contained within a small fraction of the Brillouin zone. We discuss how the effect of commensurability may arise in a 3D Dirac system in high magnetic field.