Bulk Transport Properties of MnBi2Te4 PhaseTransitions

Abstract

Crystals have been studied extensively in condensed matter systems for their potential uses in improving electronics. In this thesis, we investigate the crystal MnBi2Te4 which is a novel material that undergoes multiple metallic and topological phase transitions when the temperature, magnetic field, and thickness are tuned. We first give background on topological insulators, the quantum hall effect, and the chiral anomaly to understand the multiple phases of this crystal. We next report on transport experiments investigating these phases. In the bulk, we report that as the temperature decreases, MnBi2Te4 switches from a paramagnetic to anti-ferromagnetic phase at the Neel temperature of T ~25K. We also report the anti-ferromagnetic to canted anti-ferromagnetic transition at ~3.5T to ferromagnetic phase transition at ~8T as the magnetic field varies. We saw that these transitions disappeared as the angle of the magnetic field with respect to the applied current decreased. Lastly, we report a sign change in the thermopower at ~19K near the Neel temperature which might give evidence of the paramagnetic to anti-ferromagnetic phase transition in bulk MnBi2Te4. Because of the observation of these phase transitions, MnBi2Te4 could be a suitable candidate for making interesting electronics.