PROBING THE MAGNETIC EXCITATIONS IN FRUSTRATED MAGNETS BY OPTICAL AND ELECTRICAL TECHNIQUES

Abstract

In this thesis, we systematically studied the magnetism in two “frustrated” 2D magnets: NiI2 and α-RuCl3 by optical and electrical techniques. Two magnetic phase transitions in NiI2 are visible by tracing the temperature-dependent Raman spectrum. Two magnons show up in the spiral phase. Furthermore, the magnons are closely related to the helicity of spiral magnetism, while the anisotropy of ferroelectricity is reflected in the XX channel of Eg mode. As a result, we successfully visualized six multiferroic domains in NiI2 for the first time. In the tunneling devices of thin-layer α-RuCl3, the signature of magnons appears in the inelastic tunneling spectrum. However, the signals are quite unstable due to the instability of magnetic order. Subsequently, strong charge transfer is observed in α-RuCl3/graphene heterostructures. In the quantum Hall regime, the gate- and field-tunable asymmetry are observed. In a contrast, the asymmetry vanishes when graphene forms a superlattice with h-BN.