Exploring Magnetic Fields in Layered Materials: A New Discovery

The study of interacting topological phases has always been intriguing, with one notable example being the composite Fermi liquid, which forms in strong magnetic fields. Recently, scientists have predicted that a similar phenomenon, the zero-field composite Fermi liquid, could occur in a twisted MoTe2 bilayer, a material known for its fractional Chern insulator properties. While previous transport measurements at a specific filling factor (ν = -1/2) showed signs consistent with this zero-field composite Fermi liquid, new methods are needed to further investigate this state and its elementary excitations.Using the unique valley properties of twisted MoTe2, researchers have discovered optical signatures of a zero-field composite Fermi liquid. They measured the degree of circular polarization in trion photoluminescence, which is the light emitted when an electron and two holes combine. They found that in regions where ferromagnetism is strong, the polarization is nearly perfect. However, at certain filling factors and for a range of hole doping near ν = -1/2, this polarization is suppressed. The suppression of polarization is likely due to an energy gap, or pseudogap, in the electronic excitations of the Chern insulators. This gap prevents the formation of local spin-polarized excitations needed for trion creation. Instead, trion formation relies on optically generated unpolarized itinerant holes. This work introduces a new way to study zero-field fractional Chern insulator physics using excitonic probes, a method unique to twisted MoTe2.