Master's Defense: Frederik Knudsen Wolff

Magnetic Field Dependence of Correlated Phases in tMoTe2

We measure a sample of tMoTe2 with a twist angle of 3.9 degrees, which hosts a very versatile phase-space containing both ferromagnetic order along with topological correlated phases. In this material stack, made famous by its field-independent features at fractional hole-filling, we find several correlated insulating phases also at fractional hole-filling, which display a very versatile dependence on magnetic field. First we reproduce the quantum anomalous Hall effect at a filling of -1. We find a decreased transverse resistance of one resistance quantum at filling -2/3, while the state still acts as a state with Chern number -2/3 in magnetic field. The fractional Chern insulator at filling -2/3 turns into a topologically trivial insulator, at large out-of-plane electric field D, and that state is shown to be strongly suppressed by a magnetic field larger than 0.7T. In contradiction to this behavior, the large D insulating states at fillings -1/2, -1/3 and -1/4 are stabilized by the magnetic field. The state at filling -1/2 appears at zero magnetic field, while the states at filling -1/3 and -1/4 need a finite magnetic field, before they appear at large D. We report stabilizing fields of 0.9T and 0.7T for filling -1/3 and -1/4 respectively. We also find the Chern insulating phases to be stabilized at larger D by the magnetic field. This thesis will describe the behavior of these insulating states in detail and give possible physical mechanisms to explain their behavior.